Vol. 24 No. 4

Transcrição

Vol. 24 No. 4

Nuclear Physics News
International
Volume 24, Issue 4
October–December 2014
FEATURING:
Jyväskylä - Nuclear Lattice Simulations -
Cosmic Rays: Hurdles on the Way to Mars
10619127(2014)24(4)
Nuclear Physics News
Volume 24/No. 4
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Ari Jokinen, Jyväskylä
Hideyuki Sakai, Tokyo
Yu-Gang Ma, Shanghai
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Vol. 24, No. 4, 2014, Nuclear Physics News1
Nuclear
Physics
News
Volume 24/No. 4
Contents
Editorial
The Innovative Approach of the Last Born INFN Scientific-Technological Center
Fernando Ferroni and Graziano Fortuna.................................................................................................... 3
Laboratory Portrait
The Jyväskylä Accelerator Laboratory
Ari Jokinen.................................................................................................................................................... 4
Feature Articles
A New Tool in Nuclear Physics: Nuclear Lattice Simulations
Ulf-G. Meißner............................................................................................................................................. 11
Nuclear Structure of Light Nuclei Near Threshold
Calem R. Hoffman and Benjamin P. Kay...................................................................................................... 16
Facilities and Methods
Light Exotic Nuclei at JINR: ACCULINNA and ACCULINNA-2 Facilities
Leonid Grigorenko, Andrey Fomichev, and Gurgen Ter-Akopian................................................................ 22
Nuclear Physics at Jožef Stefan Institute
Matej Lipoglavšek and Simon Širca............................................................................................................. 28
Impact and Applications
Cosmic Rays: Hurdles on the Road to Mars
Marco Durante and Francis A. Cucinotta.................................................................................................... 32
Meeting Report
The First International African Symposium on Exotic Nuclei (IASEN2013)
Z. Vilakazi and Yu. Penionzhkevich.............................................................................................................. 35
News and Views
Nuclear Physics Research Opportunities in Brazil
Mahir S. Hussein.......................................................................................................................................... 36
2012–2014 European Nuclear Physics Dissertation Award
Douglas MacGregor..................................................................................................................................... 37
IBA-Europhysics Prize 2015 for Applied Nuclear Science and Nuclear Methods in
Medicine Call for Nominations
Douglas MacGregor..................................................................................................................................... 38
In Memoriam
In Memoriam: George Dracoulis (1944–2014)
Greg Lane, Andrew Stuchbery, Phil Walker, and Filip Kondev....................................................................... 39
Calendar.......................................................................................................................................................... 40
Cover Illustration: The Jyväskylä Accelerator Laboratory - see article on page 4.
2
Nuclear Physics News, Vol. 24, No. 4, 2014
editorial
The Innovative Approach of the Last Born INFN
Scientific-Technological Center
In January 2013, INFN established
a new scientific-technological Center in Trento, named Trento Institute
for Fundamental Physics and Applications (TIFPA). The foundation of
TIFPA represents the achievement of
a long journey of collaboration between INFN and Scientific Institutions
sited in the Trento area, among them,
Trento University (UNITN) through
the Physics Department (TPD), the
Foundation Bruno Kessler (FBK)
(former Istituto Trentino di Cultura),
and The European Center for Theoretical Studies in Nuclear Physics and Related Areas (ECT*). It is worthwhile
mentioning the important role of facilitator played by the local government
(Provincia Autonoma di Trento, PAT)
which has provided substantial financial and logistical support to most of
the successful research programs carried out jointly by INFN, UNITN, and
FBK. While the governance of TIFPA
is under the responsibility of INFN,
the Center activities are supported
(for the moment) by three partners:
UNITN, FBK, and APSS (formerly
ATreP). The Center is open to other
future partners. According to the new
Statute of INFN and to the recommendations of PAT, the mission of TIFPA
should comply with:
• Research activities conducted in
international contests
• Research activities embedded in
the territory
• Excellence of the expected results
• Innovation triggered by institutional research activities
• Transfer of knowledge to the society
TIFPA is an environment structured to intimately combine basic
science (Particle, Astroparticles, and
Nuclear Physics) activities with R&D
programs; challenges of basic science
trigger innovation; innovation makes
it possible to attach new frontiers of
knowledge. This vital circle is realized in TIFPA combining the virtues of
the INFN Sections (research activities
proposed by the scientific community
through a bottom-up debate; such a debate is organized through the five National Scientific Committees that act as
Advisory Boards of the INFN Council) with the modern organizations
devoted to innovation and knowledge
transfer (FBK). Day by day operations and mid- to long-term programs
are regulated by a Convention that also
fixes the governance of the Center.
Implementation Agreements define the
specific role of every partner. Three
important bodies are in charge to advise the director of TIFPA:
• A Committee supervising the coherence of the partner initiatives
with the general planning of the
Center. It is chaired by the director of TIFPA and composed by
one representative per partner;
• A Council of the Center in support of the director’s managing
actions. It is composed by the
traditional research group coordinators and by the supervisors
of the new-born Technological
Sectors (TSs). TSs are virtual
laboratories that include all the
infrastructures, tools, and professional skills needed to attach
R&D strategic projects, optimizing resources and timing;
• A Technical-Scientific Committee monitoring the implementation of the research programs and
their position in the international
contest.
TIFPA is an high priority initiative of the 2014–2016 Strategic Plan
of Trento University, Department of
Physics as a follow-up of the development strategy 2012–2014 approved
by PAT directed to strengthen the joint
initiatives between University and
Research National Institutions in the
Trento area. In particular, the presence of INFN in Trento will contribute
to the birth of a Center of excellence
for in space and on ground Research
in Astroparticle Physics and associated technologies. Moreover, the birth
of the proton therapy Center and the
establishment in Trento of a new research group headed by a worldwide
recognized scientist, will boost and
expand the existing research activities at the border of Physics, Biology,
and Cancer treatment, attracting a new
generation of skilled students and external additional funds.
It is expected that TIFPA will be
in full operation at the end of the year
2015.
Fernando Ferroni
INFN President
Graziano Fortuna
TIFPA Director
The views expressed here do not represent the views and policies of NuPECC except where explicitly identified.
laboratory portrait
The Jyväskylä Accelerator Laboratory
The Jyväskylä Accelerator Laboratory is a national center for nuclear
and accelerator-based research and
education. It is an integral part of the
Department of Physics, University of
Jyväskylä. The Accelerator Laboratory and the Department Physics were
moved to the current site in the early
1990s, as described in the previous
Laboratory Portrait published in 1991
[1]. Since then the research program
of the laboratory has been structured
around the main instruments and research fields, which share the available beam time. The present laboratory layout is shown in Figure 1. In
addition to basic research in nuclear
and accelerator based materials physics, beam time is reserved for commercial services.
Accelerator-based research began
in Jyväskylä in the mid 1970s with
the Scanditronix MC-20 cyclotron,
which accelerated hydrogen (p, d) and
helium (3He, 4He), running until 1991
when it was decommissioned. At that
time the K130 cyclotron [2] was being installed at the new location of
the Accelerator Laboratory in Ylistö.
The main components of the cyclotron were manufactured by Scanditronix, Sweden, with the magnet being
jointly designed by JYFL and Scanditronix.
The cyclotron first accelerated
beam in January 1992 and the first nuclear physics experiment was carried
out in 1993 when the measurement
areas were available. By 1996 the cyclotron usage exceeded 6000 h/year,
a level maintained since then. At the
end of 2013 the total run time of the
K130 cyclotron since 1993 exceeded
130,000 h.
The K130 cyclotron was mainly
designed and optimized for heavy
ions although light ions can also be
accelerated. The maximum energy is
(q/A)2 130 MeV/nucleon for all other
isotopes except protons, for which fo-
Figure 1. The present lay-out of the JYFL Accelerator Laboratory.
4
cusing limit restricts theoretical maximum energy to 90 MeV.
The beam intensity for light ions at
energies above 20 MeV/nucleon was
originally limited by beam losses in
the extraction region, the extraction
efficiency being about 50%. To overcome this limitation the cyclotron was
modified in year 2000 to allow extraction of negative ions. After this modification a proton beam current of 50
microA could be routinely provided
for radioisotope production (123I).
High demand for light-ion beams
triggered a project to acquire a dedicated cyclotron for protons and deuterons. The plan became a reality
when a 30 MeV H– cyclotron was approved on the list of equipment as partial compensation of the former USSR
debt to Finland. The contract for the 30
MeV H– cyclotron, MCC30/15, was
approved in June 2007. The cyclotron was built by NIIEFA, D.V. Efremov-Institute, St. Petersburg, Russia
[3].
Final acceptance tests were made
at JYFL in April 2010, reaching or
exceeding the specified values. The
maximum proton current at both 30
MeV and 18 MeV was 200 microA.
The maximum deuteron current at 15
MeV was 62 microA. The MCC30/15
cyclotron has two extraction ports,
one on each side of the cyclotron
(Figure 2). One beam-line serves the
IGISOL facility and the other one for
future radioisotope production.
The K130 cyclotron is served
by three ion sources. Two ECR ion
sources (6.4 and 14 GHz) produce
highly charged heavy ions and a multicusp ion source LIISA produces negative ions H– and D–. The ECR sources
and the LIISA multicusp source were
developed, designed, and (partially)
built at JYFL.
laboratory portrait
Figure 2. A new MCC30 light-ion cyclotron.
The 6.4 GHz ECRIS was the first
ion source for the K130 cyclotron.
Since then it has evolved through several upgrades and the performance has
increased accordingly. Due to demand
for higher charge states, a project to
build a modern 14 GHz ECRIS was
launched in 1999. Later, the 14 GHz
ECRIS was equipped with an auxiliary TWTA microwave transmitter to
access higher charge states, like 35+
for 131Xe beam required for space
electronics testing.
The multicusp ion sources for the
K130 cyclotron (LIISA) and Pelletron
(PELLIS) were designed and built
at JYFL. In order to extend the time
between filament changes a project
to develop an RF-driven source (RADIS) was started in 2011 [4]. Replacing the filament with an RF antenna
will extend the maintenance interval
from about 150 hours at least to one
month. This is rather crucial for reli-
able operation of the MCC30/15 cyclotron for long physics experiments
and for commercial runs.
The Ion Guide Isotope Separator
On-Line facility at JYFL
In 2012 we celebrated three decades of research following the development of the ion guide technique in
the early 1980s at the IGISOL facility.
To acknowledge this achievement, a
collection of articles, several of which
contained a significant amount of
original material, were published as
a Topical Collection in the European
Physical Journal [5] and a further 21
published in Hyperfine Interactions
[6].
The novelty of the ion guide concept and its gradual evolution has
always been driven by the pursuit of
research on both sides of the valley of
beta stability. Similar extraction effi-
ciencies for both volatile and non-volatile elements throughout the periodic
table has resulted in the production of
a rich variety of radioactive ion beams
(RIBs) of short-lived exotic nuclei
for fundamental nuclear structure research and applications.
During the 1980s, the main research activity at IGISOL was decay
spectroscopy of fission products produced in the proton-induced fission of
uranium, with the discovery and study
of approximately 40 new isotopes and
isomers using beta-, gamma-, and conversion electron spectroscopy. Following the move from the old Physics
Department to the Science Campus
of the University of Jyväskylä, the
facility was reinstalled as IGISOL-2
and served the period from 1993 to
2003.
During this time a major upgrade
to the instrumentation of the facility was realized. The Universities of
Vol. 24, No. 4, 2014, Nuclear Physics News
5
laboratory portrait
Manchester and Birmingham installed
a collinear laser spectroscopy station
in 1994 for the study of ground state
properties (nuclear spin, moments, and
mean-square charge radii) of refractory elements. In 1998 an RFQ coolerbuncher was installed to convert continuous ion beams into bunches. This
led to dramatic reductions in the scattered photon background, a technique
that has since become standard practice. The construction of the longitudinal Penning trap, JYFLTRAP, not
only afforded unique opportunities
for decay spectroscopy with isobarically purified beams, but resulted in a
hugely successful mass measurement
program.
From 2004 onward IGISOL-3 was
in operation, coupling the improved
yields with the new instrumentation to
perform precision experiments. In parallel, a rigorous development on resonance photo-ionization to address the
lack of elemental selectivity in the ion
guide technique commenced. In addition to selective RIB production, the
possibility for in-gas-cell or in-gasjet resonance ionization spectroscopy
(RIS) has been pursued, providing a
complementary approach to collinear
laser spectroscopy for the study of
nuclear structure. The backbone of the
facility is a suite of three Ti:sapphire
lasers, built in collaboration with the
University of Mainz, pumped by an
Nd:YAG laser operated at 10 kHz. In
general, the laser system is capable of
covering wavelengths ranging from
~690 nm to 1,000 nm and from ~500
nm to 205 nm with higher harmonic
generation.
At IGISOL-3, experiments covered
laser spectroscopy and decay spectroscopy in collaboration with international teams utilizing a variety of
tools including beta and gamma spectroscopy, total absorption spectrom-
etry, neutron spectroscopy, fast timing methods and in-trap techniques,
many experiments of which would
increasingly request the purification
capabilities of the Penning trap. The
workhorse of the IGISOL facility became the JYFLTRAP Penning trap,
employed in the measurement of
almost 250 atomic masses of shortliving nuclei, including measurements
of the superallowed β-decay QEC values for fundamental studies, with 14
QEC values measured to extremely
high precision between 2005 and
2010.
Operation at IGISOL-3 concluded
in June 2010. Over the following two
years the facility was moved and reconstructed in a new experimental
hall (850 m2), which also houses the
MCC30/15 cyclotron. Primary beams
can be delivered to the new IGISOL-4
facility from both cyclotrons (Figure 3). The move has offered an op-
Figure 3. A schematic lay-out of the new IGISOL-4 facility.
6
laboratory portrait
portunity to dramatically improve the
overall layout in order to overcome
several shortcomings of the previous
facility, as well as make use of a considerable increase in floor space for
future developments and more sophisticated detector setups.
In the new layout, optical transport
from two laser cabins situated directly
above the target chamber has been improved, with separate paths for up to
three laser beams to the target area for
both in-source and in-jet ionization. A
second ion source station is under construction on the second floor intended
to provide stable beams of ions from a
discharge-type and carbon cluster ion
source.
Downstream of a new electrostatic
switchyard at the mass separator focal plane, the layout of the facility
has dramatically changed. A more
advanced beam distribution system
will allow fast switching between
three beam-lines, the first housing a
permanent spectroscopic station for
on-line yield monitoring, the second
a line with additional electrostatic
elements and diagnostics for future
decay spectroscopy experiments not
requiring the Penning trap, and the
third leading to the RFQ. The collinear laser beam-line is now situated on
the ground floor. The beam from the
RFQ can either be transported left toward the laser spectroscopy station or
right toward JYFLTRAP. Such separation of collinear and trap beam-lines
enables direct access of laser light into
the RFQ for optical manipulation, ion
resonance ionization, or even polarization of ion beams, all planned as
part of an extensive laser spectroscopy
program in the future.
Presently IGISOL-4 is undergoing
full commissioning and a number of
on-line experiments have been performed as different parts of the facility
come on-line. The first experiments
have shown improvements in the yield
of mass-separated fission fragments of
up to a factor of three over IGISOL-3.
An important avenue of future research will be the push toward ever
more exotic neutron-rich species. This
will be met by a substantial research
program utilizing neutron-induced
fission of uranium and other actinide
targets. Several topical applications
related to nuclear energy including fission product yields, reactor design and
safety as well as the management of
nuclear waste are all connected to this
program. A neutron converter target is
currently under construction following detailed studies in collaboration
with Uppsala University.
Funding from the Finnish Academy has been awarded for additional
ion manipulation tools which can be
directly connected to the beam-lines
after the RFQ. One such device will
be a multi-reflection time-of-flight
mass spectrometer. Other devices under construction or planning include a
cone trap for laser spectroscopy and
a cryocooler. In close collaboration
with the neighboring RITU/GAMMA
group, plans are being made for the
development of a gas cell for the focal
plane of the new MARA recoil separator.
JYFL Nuclear Spectroscopy Group
Over the past fifteen years or so,
the “RITU” and “GAMMA” groups of
JYFL have combined forces to great
effect and made rapid advances in the
experimental study of nuclear structure of heavy and neutron-deficient
nuclei. Assisted by close collaboration
with a large number of international
institutions, the instrumentation available for in-beam and decay spectroscopic studies has steadily expanded.
Most notable of the collaborations is
that with the UK community, which
has resulted in the deployment of the
GREAT spectrometer and associated
Total Data Readout (TDR) acquisition
system at JYFL. In addition to these,
the SAGE (Silicon And GErmanium)
and LISA (Light Ion Spectrometer Array) spectrometers have been successfully used in recent experimental campaigns (University of Liverpool and
Daresbury Laboratory). The group at
the University of York has been instrumental in improving the sensitivity for
challenging studies of N ≈ Z nuclei,
through the so-called beta-tagging
technique.
Further significant input has come
from the French community, especially IPHC Strasbourg, CEA Saclay,
and CSNSM Orsay. The group at
Strasbourg managed to produce an
enriched volatile MIVOC compound
containing 50Ti, which in turn led to
the long-awaited in-beam study of
256Rf.
The main workhorse of the Nuclear
Spectroscopy group is the RITU gasfilled recoil separator, which was originally built to study the decay properties of heavy nuclei [7] (Figure 4).
At the time of construction, no-one
would have imagined the versatile
and wide-ranging use of the separator today. For typical fusion evaporation reactions, RITU has a transmission from around 10% to better than
50%. Almost continually since the
late nineties, RITU has been coupled
to an array of germanium detectors
at the target position. This coupling
allows the in-beam study of nuclei
produced with low cross sections, by
employing the Recoil-Decay Tagging
(RDT) technique. From humble beginnings with the small DORIS array
of TESSA detectors, the detection efficiency for gamma rays at the target
position has increased. The current
array is JUROGAMII, which consists of 24 Clover detectors and up
to 15 Tapered detectors along with
their associated Compton-suppression
shields. In parallel, the sensitivity of
Vol. 24, No. 4, 2014, Nuclear Physics News
7
laboratory portrait
Figure 4. A gas-filled recoil spectrometer RITU.
the focal plane detection systems has
also developed over the years. The
first developments were made by the
in-house group, with the addition of
transmission gas detectors to allow the
discrimination of scattered beam and
other unwanted particles. The use of a
transmission detector in “veto” mode
also eliminated the need to use slowpulsed beams in decay experiments.
These developments were superseded
with the installation of the GREAT
spectrometer and the associated TDR
acquisition system. The introduction
of the triggerless TDR system eliminated problems due to common dead
time and also eliminated the need to
run “surrogate” reactions in order to
set-up the timing electronics.
These developments meant that
JYFL became one of the leading laboratories for studies of nuclei far from
stability, with a very busy experimental program. Currently the group performs something like 10–15 experiments per year, of typical duration one
to two weeks.
In the past few years, our collaborations have again borne fruit, with
the commissioning and exploitation of
8
new devices coupled to RITU. A collaboration of the University of Liverpool, Daresbury Laboratory, and the
local group led to the development of
the SAGE spectrometer, designed for
simultaneous in-beam studies of internal conversion electrons and gamma
rays. The development of SAGE also
relied on the parallel development of
digital electronics to instrument the
large number of channels of silicon
and germanium detectors. Currently
all channels are instrumented with
Lyrtech VHS-ADC electronics, allowing the use of higher counting rates
and further lowering the limit of sensitivity. SAGE has completed three
campaigns of experiments, and data
are under analysis.
The LISA spectrometer (again
through Liverpool and Daresbury)
completed a campaign of experiments
in early 2013. LISA is an array of
silicon detectors designed to observe
charged particles emitted in the decay
of short-lived (ns) states at the target
position of RITU. Again, data from
the campaign is under analysis and
further experimental campaigns are
being planned.
JYFL has had a very successful collaboration with the group at Cologne,
expert in lifetime measurements with
plunger devices. This collaboration
has made a number of experiments
to study the lifetimes of nuclei close
to 186Pb, one of the most well-known
regions of nuclei exhibiting shape
coexistence phenomena. Following
on from this, an updated version of
the Cologne plunger device has been
constructed at the University of Manchester, known as DPUNS. The collaboration consisted of the Universities of Manchester and Liverpool, the
IKP Köln group, and the local group at
JYFL. DPUNS has been successfully
used in a number of experiments, and
first results have been published. AQ1
As mentioned above, another line
of study has been to employ the recoil-beta tagging technique in order
to investigate N ≈ Z in the mass 70
region. It is perhaps these studies that
are the most surprising to be found
in the RITU experimental program,
given that RITU was developed for
studies of heavy elements. The success here is largely due to the efforts
of the group at the University of York,
who have developed a variety of new
detectors, both as extensions of the
GREAT focal plane spectrometer and
for use at the target position. The most
recent of these is the “UoYTube” detector, an array of CsI detectors that
is used to detect (and veto) charged
particles emitted at the target position.
The limit of sensitivity now such that
studies of 66As and 66Se have recently
been carried out.
The local group, in parallel to
running the experimental campaign
at RITU, is currently constructing
the new Mass Analysing Recoil Apparatus (MARA) spectrometer. In
the space vacated by IGISOL in the
cave adjoining that of RITU, the new
vacuum-mode mass spectrometer is
taking shape. MARA will allow stud-
laboratory portrait
Figure 5. Installation of the electrodes of the high-voltage deflector of MARA
separator.
ies of lighter nuclei than at RITU,
broadening the region of the nuclear
chart accessible for in-beam studies
at JYFL. It is envisaged that the wide
range of instrumentation available for
use with RITU will also be used at
MARA. The ion optics of the beamline to MARA have also been planned
to take this into account.
MARA consists of a magnetic
quadrupole triplet, electrostatic dipole deflector, and magnetic dipole,
to separation of fusion-evaporation
products according to their mass-tocharge ratio. The majority of components for MARA are already installed
including the electrostatic deflector
delivered by Danfysik earlier this
year (Figure 5). It is hoped that the
first beam tests will be made in the
beginning of 2015.
Accelerator-Based Materials
Research and Ion Beam Analysis
The two main focus areas in accelerator-based materials research are the
understanding of the basic phenomena
related to the ion–matter interaction,
for instance energy straggling of ions
[8], and utilizing these phenomena in
materials modification and characterization [9]. The main research instrument of the group is a 1.7 MV Pelletron tandem accelerator (Figure 6),
which can deliver beams of H to Au
from three different ion sources with
a final energy of 0.2–20 MeV. Four
beam-lines are used for ion beam
analysis and ion beam lithography.
The group is also a frequent user of
the K130 cyclotron for instance, in ion
track–related research.
The development of ion beam
analysis techniques involves new detectors, data acquisition using direct
digitization, and in-house analysis
software development. The workhorse
in ion beam analysis is a time-of-flight
elastic recoil detection analysis (TOFERDA) setup, which can be utilized
for depth profiling of all elements in
thin films down to single nanometer
depth resolution. This has proven to
be a very powerful tool, especially in
the analysis of atomic layer deposited
(ALD) thin films, which often contain light impurities such as hydrogen
and carbon. The latest development in
2013 was the installation of a superconducting microcalorimeter detector
in collaboration with a group from
the NanoScience Center for particleinduced X-ray emission (PIXE) measurements. The detector has 3 eV energy resolution at 5.9 keV, and therefore offers unique possibilities for
chemical analysis of thin films and
also culture heritage artefacts.
The materials research group has
close connections to Finnish industry via regular collaborative projects. These projects have involved,
for instance, detector development,
biomimetic thin films, and ion beam
analysis.
Figure 6. A lay-out of the Pelletron laboratory with three ion sources and four
beam-lines.
laboratory portrait
of the car and health care industries.
For this application, stable and intense
heavy ion beams have been developed.
Figure 7. A radiation test facility RADEF.
Industrial Applications at JYFLACCLAB
Isotope production with the K-130
cyclotron started in 2000 and in 2002
it was at a level of weekly production.
The isotope 123I was produced for a
local medical company, which supplied the final pharmaceuticals to all
the biggest hospitals in Finland. Currently, iodine production is halted, but
plans to begin radioisotope production
with the MCC30/15 accelerator are in
progress.
The increased demands for radiation testing in Europe attracted ESA
to the JYFL Accelerator Laboratory.
In 2004 a contract between ESA and
JYFL for the “Utilisation of the HighEnergy Heavy Ion Test Facility for
Component Radiation Studies” was
signed. After the upgrade of the station was completed in May 2005, the
RADiation Effects Facility, RADEF,
qualified as one of ESA’s External
European Component Irradiation
Facilities (ECIF). RADEF includes
10
heavy-ion and proton beam-lines for
the irradiation of space electronics
in the same facility. It consists of a
chamber whereby tests can be made
either in vacuum or in air, and equipment for beam quality and dosimeter
analysis is provided. A user interface
for monitoring flux and fluence was
also developed. A schematic picture of
the set-up of beam-lines is shown Figure 7. RADEF’s other specialty is the
high penetration ion cocktail developed during the upgrade. It consists of
seven ion species with energies of 9.3
MeV/nucleon.
During its operation RADEF has
served as a test site for about 35 companies and space organizations. In
addition to ESA, the list of institutes
includes NASA/JPL, JAXA, INTA,
CNES, CEA, SANDIA, and ONERA.
From the beginning of 2008
RADEF has also irradiated membranes for a Swiss-German company.
The final products are micro filters
mainly manufactured for the needs
Outlook
Research and development has
been a priority at the JYFL Accelerator Laboratory since the first beams
were delivered in the early 1970s.
The last two decades have shown an
increase of applied and commercial
research utilizing the accelerators;
reaching about 25% of the total beam
time at present. The division between
basic research and applications is expected to stay at that level in the coming years. New installations under
construction and planned upgrades
will provide a firm basis for the successful operation of the Accelerator
Laboratory well into the coming decade and beyond.
References
1. J.Äystö and A. Pakkanen, Nucl. Phys.
News 1 (5) (1991) 6.
2. E. Liukkonen, Proc. 13th Int. Conf.
On Cyclotrons and Their Applications
(Vancouver, Canada, 1992) 22.
3. P. Heikkinen, Proc. 19th Int. Conf. on
Cyclotrons and Their Applications
(Lanzhou, China, 2010) 310.
4. T. Kalvas, O. Tarvainen, J. Komppula,
et al., Recent Negative Ion Source Activity at JYFL, AIP Conf. Proc. 1515
(2012) 349.
5. European Physical Journal A 48 (4)
(2012).
6. Hyperfine Interactions 223 (1–3)
(2014).
7. M. Leino et al., Nucl. Instr. Meth.B 99
(1995) 653.
8. C. Vockenhuber, J. Jensen, J. Julin, et
al., Europ. Phys. J. D 67 (2013) 145.
9. A. R. A. Sagari, J. Malm, M. Laitinen,
et al., Thin Solid Films 531 (2013) 26.
AQ2
Ari Jokinen
Affiliation???
feature article
A New Tool in Nuclear Physics:
Nuclear Lattice Simulations
Ulf-G. Meißner1,2,3
1Helmholtz-Institut für Strahlen- und Kernphysik and BCTP, Universität Bonn, Nußallee 14-16,
D-53115 Bonn, Germany
2Forschungszentrum Jülich, IAS-4, IKP-3, JCHP and JARA HPC, D-52425 Jülich, Germany
3Kavli Institute for Theoretical Physics China, CAS, Beijing 100190, China
Introduction
The nuclear many-body problem continues to be one of
the most interesting and demanding challenges in contemporary physics. With the advent of FAIR, FRIB, and the
many existing radioactive ion beam facilities, a detailed
and accurate theoretical understanding of nuclear structure and reactions is mandatory. A major breakthrough in
nuclear theory was initiated through the work of Steven
Weinberg [1], who made the first steps for an effective field
theory (EFT) solution of the nuclear force problem. In this
approach, two- and multi-nucleon forces as well as the response to external electromagnetic and weak probes can
be calculated systematically, precisely, and consistently. In
addition, the so important issue of assigning theoretical errors can be dealt with naturally. The very hot topic of the
quest for three-nucleon forces was already addressed in
this journal [2], which also contained a short introduction
into the framework of chiral nuclear EFT. In this scheme,
the nuclear forces are given in terms of one-, two-, … pion
exchanges and smeared local multi-nucleon operators, that
parameterize the short-distance behavior of the nuclear
forces. These operators come with unknown coupling constants, the so-called low-energy constants (LECs) that must
be determined from a fit to nucleon-nucleon scattering and
a few three-body data. For systems up to four nucleons,
these forces have been tested in extensive detail and scrutinized. One of the present research foci is the calculation
and investigation of higher order corrections to the threenucleon forces as well as the construction of electroweak
current operators. For reviews on the method and many results see Refs. [3, 4].
But what about larger nuclei? There are two different
venues. The first one is to combine these chiral forces,
eventually softened using renormalization group methods,
with well-developed many-body approaches like the nocore-shell model, the coupled cluster approach and so on.
There have been quite a few activities in such type of ap-
proaches (see Refs. [5–10]) for some recent works. Another
approach, and this is the one I will discuss in what follows,
is to combine the chiral forces with Monte Carlo simulation
techniques, that have been successfully applied in gauge
field theory (lattice QCD), condensed matter systems and
other areas of physics. This novel method will be called
nuclear lattice simulations (or nuclear lattice EFT) in the
following.
In this short review, I first introduce the formalism in a
very simplified manner and discuss the scope of the method,
then show a few assorted physics results and finally address
the question about the viability of carbon-oxygen based life
on Earth when one changes certain fundamental parameters
of the Standard Model that control nuclear physics.
Formalism and Scope
The basic ingredient in this framework is the discretization of space–time (see Ref. [11] for details). Space–time is
represented by a grid. This lattice serves as a tool to compute the nuclear matrix elements under consideration. More
precisely, one first performs a Wick rotation in time so that
the time evolution operator behaves as exp(-Ht), with H the
nuclear Hamiltonian. Space–time is then coarse-grained as
shown in Figure 1. In the three spatial directions, the smallest distance on the lattice is given by the lattice spacing a,
so that the volume is L × L × L, with L = N a and N an integer, whereas in the time direction one often uses a different
spacing at, and Lt = Nt at is chosen as large as possible.
Typical values are N = 6 and Nt = 10...15. As the Euclidean
time becomes very large, one filters out the ground state as it
has the slowest fall-off ~exp(-E0t), with E0 the ground state
energy. Excited states can also be investigated. This, however, requires some more effort. The nucleons are placed on
the lattice sites as depicted in Figure 1. Their interactions
are given by pion exchanges and multi-nucleon operators,
properly represented in lattice variables. So far, nuclear lat-
feature article
n
p
n
a
~ 2 fm
Figure 1. Two-dimensional representation of the space–
time lattice. The smallest length on the lattice is the lattice
spacing a, and the protons (p) and neutrons (n) are placed
on the lattice sites.
tice simulations have been carried out using two- and threenucleon forces at next-to-next-to-leading order (NNLO)
in the chiral expansion. The Coulomb force and isospinbreaking strong interaction effects are also included, thus
one has all required ingredients to describe the structure of
nuclei. The lattice is used to perform a numerically exact
solution of the A-nucleon system, where the atomic number
A = N + Z counts the neutrons and protons in the nucleus
under investigation.
It is important to realize that the finite lattice spacing
entails a maximum momentum pmax = π/a, so that for a
typical lattice spacing of a = 2 fm, one has a maximum
momentum of about 300 MeV; that is, one deals with a
very soft interaction. The main advantage of this scheme is,
however, the approximate spin-isospin SU(4) symmetry of
the nuclear interactions already realized by Wigner in 1937
[12]. Because of this approximate symmetry, the malicious
sign oscillations that plague any fermion simulation at finite
density are very much suppressed, quite in contrast to the
situation in lattice QCD. A lucid discussion of this issue has
been given by Chen, Schäfer, and Lee [13]. Consequently,
alpha-type nuclei with N = Z, and spin and isospin zero
can be simulated most easily. However, in the mean time
our collaboration has developed a method that allows for a
remarkable suppression of the remaining sign oscillations
in nuclei with N ≠ Z. One more remark on the formalism
is in order. The simulation algorithms sample all possible
configurations of nucleons, in particular one can have up
to four nucleons on one lattice site. Thus, the so important
12
phenomenon of clustering in nuclei arises quite naturally in
this novel many-body approach.
In Figure 2, the phase diagram of strongly interacting
matter is shown in the standard temperature versus density
plot. Apart from nuclear structure research, nuclear lattice
simulations can also be used to explore nuclear matter,
neutron matter or other more exotic phases as indicated by
the dark (blue) area. For comparison, the part of the phase
diagram accessible to lattice QCD is depicted by the light
(yellow) area, which is much narrower because of the sign
oscillations discussed earlier. Therefore, we can systematically explore many fascinating aspects of strongly interacting matter, but for this short review I concentrate on some
recent results pertinent to the structure of nuclei.
Assorted Results
Before presenting results, we must fix parameters. We
have nine LECs related to the two-nucleon force that can
be fixed from the low partial waves in neutron-proton scattering. Two further LECs from isospin-breaking four-nucleon operators are fixed from the nn and the pp scattering
lengths, respectively. In addition, one has two LECs appearing in the three-nucleon force, that can, e.g., be fixed from
Accessible by
Lattice QCD
100
T [MeV]
p
quark-gluon
plasma
early
universe
heavy-ion
collisions
10
Accessible by
Lattice EFT
gas of light
nuclides
nuclear
liquid
excited
nuclei
superfluid
neutron star crust
1
10-3
neutron star core
10-2
10-1
ρ
[fm-3]
ρN
1
Figure 2. Phase diagram of strongly interacting matter.
Here, ρ denotes the density, with ρN the density of nuclear
matter, and T is the temperature. For further details, see the
text. Figure courtesy of Dean Lee.
the triton binding energy and the doublet neutron-deuteron
scattering length. The first non-trivial prediction is then the
binding energy difference of the triton and 3He, we find
E(3H) - E(3He) = 0.78(5) keV, in good agreement with the
empirical value of 0.76 keV [14]. That we can reproduce
this small effect with good accuracy gives us confidence
that we have all aspects of the strong and electromagnetic
forces relevant to nuclear physics under control.
If one invents a new theoretical scheme, it is absolutely
necessary to solve a problem which other methods could
not deal with, otherwise this new approach is not accepted
easily in the community. Therefore, the first nucleus we
investigated was 12C, more precisely the ground state and
its low-lying even-parity excitations. The most interesting
excited state in this nucleus is the so-called Hoyle state
that plays a crucial role in the hydrogen burning of stars
heavier than our sun and in the production of carbon and
other elements necessary for life. This excited state of the
carbon-12 nucleus was postulated by Hoyle [15] as a necessary ingredient for the fusion of three alpha particles to
produce a sufficient amount of carbon at stellar temperatures. Without this excited state that is located very close
to the 4He + 8Be threshold (thus leading to a resonant enhancement of the production rate), much too little carbon
would be generated and consequently also much too little
oxygen, thus making life on Earth impossible. Although
the Hoyle state was seen experimentally more than a half
century ago [16], nuclear theorists have tried unsuccessfully to uncover the nature of this state from first principles. Using nuclear lattice simulations, we could perform
an ab initio calculation of this elusive state [17]. Here,
by ab initio we mean that all parameters appearing in the
nuclear forces have been determined in the two- and threenucleon systems and that the 12 particle problem has been
solved numerically exactly using Monte Carlo techniques.
The resulting spectrum of the lowest states with even parity is shown in Figure 3. One observes a nice agreement
between theory and experiment. Not only does one get the
Hoyle state at its correct position but also the much investigated 2+ excitation a few MeV above it. Further insight
into the structure of the Hoyle state was obtained in Ref.
[18], where the structure of these states was investigated.
In all these states, alpha clustering plays a prominent role.
For the ground state and the first excited 2+ state, one finds
a compact triangular configuration of alpha clusters. For
the Hoyle state and its 2+ excitation, however, the dominant contribution is a “bent arm” or obtuse triangular alpha
cluster configuration. A remaining challenge is the calculation of radii and transition moments beyond leading order
so as to make contact to the precise measurements of elec-
E [MeV]
feature article
−82
−84
2+
−83(3)
0+
0+
2+
2+
−84.51
−86
−88
2+
−82.6(1)
−87.72
−85(3)
Hoyle
−88(2)
−90
−92
0+
0+
−92.16
−92(3)
Exp
Th
Figure 3. Even-parity spectrum of 12C. On the left, the
empirical values are shown, whereas the right column displays the nuclear lattice simulation results from Ref. [16].
tromagnetic observables performed, for example, at the SDALINAC in Darmstadt [19].
Another alpha cluster-type nucleus is 16O, that also
plays an important role in the formation of life on Earth.
Since the early work of Wheeler [20], there have been several theoretical and experimental works that lend further
credit to the cluster structure of 16O. However, no ab initio
calculations existed that gave further support to these ideas.
This gap was filled in Ref. [21] where nuclear lattice simulations have been used to investigate the low-lying evenparity spectrum and the structure of the ground and first
few excited states. It is found that in the spin-0 ground state
the nucleons are arranged in a tetrahedral configuration
of alpha clusters (Figure 4). For the first 0+ excited state,
the predominant structure is given by a square arrangement of alpha clusters, as also shown in Figure 4. There
are also rotational excitations of this square configurations that include the lowest 2+ excited state. These cluster
configurations can be obtained in two ways. First, one can
investigate the time evolution of the various cluster configurations shown in Figure 4 and extract, for example, the
corresponding energies as the Euclidean time goes to infinity. Second, one can also start with initial states that have
no clustering at all. One can then measure the four-nucleon
correlations. For such initial states, this density grows with
time and stays on a high level. For the cluster initial states,
these correlations start out at a high level and stay large as
a function of Euclidean time. This is a clear indication that
the observed clustering is not build in by hand but rather
feature article
(a)
(b)
Figure 4. Schematic illustration of the alpha cluster states
in the tetrahedral (left panel) and the square (right panel)
configuration.
follows from the strong four-nucleon correlations in the
nucleus.
16O
Anthropic Considerations
Another fascinating aspect of this method is that it allows one to test the changes of the generation of the liferelevant elements under variations of the fundamental
constants of the Standard Model. For the case of nuclear
physics, these are the light quark masses and the electromagnetic fine structure constant αEM. While the light
quarks generate only a small contribution to the mass of
the nucleon—showing that mass generation is not entirely
given by the Higgs boson—their masses are comparable to
the typical binding energy per nucleon. Therefore, variations in the quark masses will lead to changes in the nuclear
binding. In fact, nuclear binding appears to be fine-tuned by
itself. A deeper understanding of this particular fine-tuning
in Nature has so far been elusive.
The already discussed Hoyle state has often been heralded as a prime example of the anthropic principle, that
states that the possible values of the fundamental parameters are not equally probable but take on values that are
constrained by the requirement that life on Earth exists. A
crucial parameter in the triple-alpha reaction rate is the difference between the Hoyle state energy and three times the
alpha nucleus mass, ΔE = 380 keV. Already in 2004, Schlattl
et al. [22] showed that ΔE could be changed by about ±100
keV so that one still produces a sufficient amount of carbon
and oxygen in stars. This is a 25% modification that does
not appear very fine-tuned. But how does this translate into
the fundamental parameters of the Standard Model (i.e.,
into changes of the light quark mass and the fine structure
14
constant)? This can be answered by employing the chiral
EFT approach to the nuclear forces. In fact, as in QCD the
pion mass squared is proportional to the sum of the light up
and down quark masses, we simply need to study the variation of the forces under changes of the pion mass. This has
been done to NNLO in the chiral expansion in Ref. [23],
where also constraints on quark mass variations from the
abundances of the light elements from the Big Bang were
derived. Armed with that, in Ref. [24] a detailed study of
the resonance condition in the triple alpha process was performed, leading to the conclusion that quark mass variations of 2 to 3% are not detrimental to the formation of life
on Earth. However, this number is afflicted with a sizeable
uncertainty that can eventually be overcome from lattice
QCD studies of the nucleon-nucleon scattering lengths. It
could also been shown that the various fine-tunings in the
triple alpha process are correlated, as had been speculated
before [25]. Further, the possible variation of the fine structure constant can be also derived, changes in αEM of ±2.5%
are consistent with the requirement that ΔE changes by at
most 100 keV in magnitude.
Consequently, the light quark masses and the fine structure constant are fine tuned. Beyond these rather small
changes in the fundamental parameters, the anthropic principle appears necessary to explain the observed abundances
of 12C and 16O. For a recent review on the applications of
the anthropic principle, the reader is referred to Ref. [26].
Summary and Conclusions
In this article, I have given a short review about the
novel method of nuclear lattice simulations and showed
some first promising results for nuclei. In addition, an application to testing the anthropic principle, which has consequences much beyond nuclear physics, was discussed. Of
course, there remains much work to be done. In particular, the removal of lattice artefacts through the finite lattice
spacing and the finite volume has to be further improved
(see, e.g., the recent work on the restoration of rotational
symmetry for cluster states [27]). In addition, the methods
to reduce the errors in the extraction of the signals from
the Euclidean time interpolation have to be sharpened, at
present ground state energies of nuclei up to A = 28 can
be extracted with an accuracy of 1% or better [28]. The
computing time scales approximately as A2, so that heavier
nuclei can also be investigated in the future. Further, the
underlying forces have to be worked out and implemented
to NNNLO in the chiral expansion. Another line of research
is to allow for the continuum limit a → 0 by formulating
the EFT with a cut-off on the lattice. A first step was done
in Ref. [29]. Another area of research concerns the equation
feature article
of state of neutron and nuclear matter and the possibility of
various pairing phenomena in such dense systems. Finally,
preliminary investigations toward the inclusion of hyperons
are also done to tackle problems in hypernuclear physics.
There is a bright future for applying and improving nuclear
lattice simulations and I would like to see more groups employing this powerful tool.
Acknowledgments
I thank all members of the NLEFT collaboration for
sharing their insight into the topics discussed here, especially Dean Lee, Timo Lähde, and Evgeny Epelbaum. I also
thank Evgeny Epelbaum and Dean Lee for comments on
the article and for help with this strange type-setting system. Computational resources were provided by the Jülich
Supercomputer Center and the RWTH Aachen. Work supported in part by the BMBF, the DFG, the HGF, the NSFC
and the EU.
11. B. Borasoy et al., Eur. Phys. J. A31 (2007) 105.
12. E. Wigner, Phys. Rev. 51 (1937) 106.
13. J.-W. Chen et al., Phys. Rev. Lett. 93 (2004) 242302.
14. E. Epelbaum et al., Phys. Rev. Lett. 104 (2010) 142501.
15. F. Hoyle, Astrophys. J. Suppl. 1 (1954) 121.
16. C. W. Cook et al., Phys. Rev. 107 (1957) 508.
19. M. Chernykh et al., Phys. Rev. Lett. 98 (2007) 032501.
20. J. A. Wheeler, Phys. Rev. 52 (1937) 1083.
22.H. Schlattl et al., Astrophys. Space Sci. 291 (2004) 27.
23. J. C. Berengut et al., Phys. Rev. D87 (2013) 085018.
24. E. Epelbaum et al., Phys. Rev. Lett. 110 (2013) 112502; Eur.
Phys. J. A49 (2013) 82.
25. S. Weinberg, Facing Up (Harvard University Press, Cambridge, USA, 2001).
26. A. N. Schellekens, Rev. Mod. Phys. 85 (2013) 1491.
27. B.-N. Lu et al., Phys. Rev. D 90 (2014) 034507.
28. T. Lähde et al., Phys. Lett. B732 (2014) 110.
29. I. Montvay and C. Urbach, Eur. Phys. J. A48 (2012) 38.
References
1. S. Weinberg, Nucl. Phys. B363 (1991) 3.
2. N. Kalantar-Nayestanaki and E. Epelbaum, Nucl. Phys. News
17 (2007) 20.
3. E. Epelbaum, H.-W. Hammer and U.-G. Meißner, Rev. Mod.
Phys. 81 (2009) 1773.
4. D. Entem and R. Machleidt, Phys. Rep. 503 (2011) 1.
5. G. Hagen et al., Phys. Rev. Lett. 109 (2012) 032502.
6. D. Jurgensen et al., Phys Rev. C87 (2013) 054312.
7. R. Roth et al., Phys. Rev. Lett. 107 (2011) 072501.
8. H. Hergert et al., Phys. Rev. C87 (2013) 034307 .
9. V. Soma et al., Phys. Rev. C87 (2013) 011303.
10. A. Lovato et al., Phys. Rev. Lett. 111 (2013) 092507
Ulf-G. Meißner
Filler?
feature article
Nuclear Structure of Light Nuclei Near Threshold
Calem R. Hoffman and Benjamin P. Kay
Physics Division, Argonne National Laboratory, Argonne, IL 60439, USA
Introduction
Moving toward an understanding of nuclei at the threshold of nuclear binding is a major theme of contemporary
experimental and theoretical nuclear physics. The challenge
to the former is to probe nuclei at the limits of existence
requiring a variety of different techniques such as nucleon
transfer, nucleon knockout, and Coulomb dissociation, and
so on. And to the latter, a question of framing the problem:
What role does finite binding play? What role does the continuum play? How can the action of these effects be isolated
when interpreting the experimental data? Is it even possible
to disentangle these?
The last few decades have seen an explosion in the
amount of available data on such systems, from heavy
neutron-deficient systems, to light nuclei-rich nuclei, pav-
13
11
9
7
6
4
3
B
Be
Li
5
He
4
8
7
Li
6
He
5
N
12
C
11
B
10
Be
9
C
10
B
9
Be
8
O
Li
7
He
6
14
O
N
13
C
12
B
11
10
He
8
He
9
7
14
B
Li
He
C
12
9
O
15
13
Li
8
16
N
C
11
Li
O
14
Be
Be
10
N
15
B
Be
13
12
N
11
He
10
O
19
N
17
N
18
C
16
B
15
16
15
B
14
Li
18
O
C
Be
Li
17
13
Be
12
Li
14
O
19
C
18
17
B
16
15
O
N
C
Be
20
B
Be
17
16
ing the way for systematic studies. In this article we focus
our attention on the neutron excitations in neutron-rich nuclei between helium and oxygen. It is within this relatively
small range of protons, two to eight, that we see the demise and creation of shell gaps [1], perhaps most notably
remarked on by Talmi and Unna in 1960 with regards to
the anomalous 1/2+ 11Be ground state [2], the existence of
halos [3], and cluster structures [4]. It is clear that this region offers a fertile ground for nuclear-structure studies and
why it has been capturing the attention of the field over half
a century.
Figure 1 shows the landscape in which these nuclei reside as a function of proton and neutron number. The inset is a compilation of single-particle neutron 0p1/2, 1s1/2,
and 0d5/2 excitations relative the neutron threshold for the
21
O
N
20
C
19
B
18
Be
22
23
O
24
N
22
N
23
C
21
C
22
O
N
21
C
20
B
19
O
N
C
25
O
24
N
26
25
O
27
O
28
O
N
N = 5 7 8 9 10 11 13
B
4
1/2
3
–
+
1/2
+
5/2
2
He
Stable
Unstable
Unbound
s and d known
p, s, and d known
En (MeV)
1
0
–1
–2
–3
–4
–5
2 3 4 5 6 7 8 2 3 4 5 6 7 8 2 3 4 5 6 7 8
Z
Z
Z
Figure 1. A portion of the Segre chart for isotopes between helium and oxygen highlighting the isotopes for which there
is information available on the energies of the neutron 0p1/2 (1/2–), 1s1/2 (1/2+), and 0d5/2 (5/2+) orbitals. These data are
shown in the plots relative to neutron threshold. The dashed lines are merely to guide the eye. The origins of the data are
summarized in Ref. [5].
16
assigned to the cross sections to take into account the effect of
the uncertainties in: target thickness, detector efficiencies, and
solid angles.
Finally, the corresponding spectroscopic factors C 2 S were
deduced by the normalization of the DWBA calculations to the
measured angular distributions. The error on the normalization
week ending
statical
are ∼ 10%,
and the
V I E W Ldue
E TtoT E
R S and systematic errors
24 SEPTEMBER
2010
uncertainties arising from the choice of potential in the DWBA
8 calculations
are estimated
to bechart.
∼ 20%These
[43]. data,
Table with
I liststhe
the
nuclei
highlighted
in the Segrè
0.000;
0+subject
S, which
areNin=reasonable
agreement
with
those
C 2(a)
exception
of
the
11
and
13
isotones,
were
the
of
1 taken from
7
the literature.
a recent
study exploring the role of finite binding on shell
Table II.
structure.
We will discuss these results in detail in the next section,
9
The experimental
angular
three
states
He is
found
at
although
we note here
that thedistributions
ground statefor
ofthese
are
presented
in
Fig.
4.
Error
bars
take
into
uncer180 ± 85 keV above the neutron threshold. Thisaccount
is compatible
tainties
thep)subtraction
of the
different
with the due
otherto(d,
reaction [26,27]
studies.
Bothbackgrounds.
the position
These
arethe
compared
withstate
the results
of
and theangular
rather distributions
small width of
first excited
are also
full
finite range
DWBAprevious
calculations,
similar[8,10,22,23,26].
to those carried
compatible
with several
experiments
out for the d(16 O,p)17 O reaction. The normalization for each
energy and transferred angular momentum L was obtained
110a log-likelihood fit.
with
20
100
The entrance channel d+ 8 He optical model potential was
15
90
calculated
using the global parameters of Daehnick et al. [45]
and80the exit
channel p+ 9 He potentials employed the sys10
tematics
of Koning and Delaroche [46]. The deuteron internal
70
5
wave
60 function, including the small D-state component, was
calculated
using the Reid soft-core interaction [47] as the
0
50
-1
0
1
2
neutron-proton
binding
potential.
We used the weak binding
40
energy approximation (WBEA) where the 9 He internal wave
30
functions
were calculated by binding the neutron to the 8 He
20
core with a standard Woods-Saxon potential with reduced
10 r0 = 1.25 fm, and diffusivity a0 = 0.65 fm, the well
radius
Counts/220 keV
Counts/220 keV
feature article
6E exp – ∆E WS (MeV)
dσ/dΩ
(mb/sr)
dσ/dΩ
(mb/sr)
dσ/dΩ
(mb/sr)
dσ/dΩ
(mb/sr)
+
+
E n1/2 – E n5/2 (MeV)
Counts/8 keV
P
EpE (MeV)
(MeV)
overlaps for tw
in a relative s
in a virtual stat
the absence of
the “binding”
modeling of t
Secondly, whil
as true resonan
difficult to achi
therefore chose
+
overlaps
for the
1.766; 2
6
1
structure
changes [5]. Most striking is the behavior
of the
The proced
+ excitations (1s ) compared to both the 1/2+– (0p )
1/2
5
assuming angu
3.027; 0
1/2 IV. RESULTS
1/2
2
relative to the
and 5/2+ (0d5/2) trends, with the first8showing
a tendency
to
+
9
2
4
analysis procedure for the d( He, He)p3.986;
2
the resulting a
lingerThe
below
the neutron threshold, changing inmeasurement
energy
by
were identical to the test experiment. The
missing
3+ mass
+ 4.088;
to deduce the
3
1
only
~4 MeV,is while
at theinsame
the 5/2the
state
changes
spectrum
presented
Fig.time
3. Since
experimental
to the spin-par
2s states
by
~8
MeV.
It
is
on
this
unique
feature
of
neutron
2 resolutions obtained with the 320 and 550 µg/cm targets
as spectroscop
thatwere
wesimilar,
will focus,
complementing
thetherecent
we present
here the sum of
spectraNuclear
obtained
complex remn
1
Physics
News
articleNote
on that
physics
the neutron
dripwith both
targets.
here beyond
the rest mass
m4 in Eq.
(1)
either post- or
8
defined as the sum of the He and free neutron rest masses.
line
0 is [6].
Since the
0
-350
-300
-250
-200
-150
-100
-50
0
2
3
4 week
5 ending
6
7
) is
The-400
calculated
missing
mass
energy
ErV
P H Y(denoted
S I9C Ahere
L as
RE
I E W L E T-2T E -1R S 03-body1
Z (mm)
5-body 7-bo24
E
[MeV]
influence
of de
2010
PRL 105, 132501 (2010) z (mm)
dy SEPTEMBER
E (MeV)
thus defined from the neutron threshold of He.
1
test this we perf
10
250
G
.
S
.
(
D
W
B
A
)
G
.
S
.
(
C
C
B
A
)
Two peaks can clearly be seen: one approximately
200 keV
+ +
FIG. 3. (Color online) Experimental missingþmass spectrum for
(CCBA) calcul
Experimental
Data
(b)
22 /3
+ another
(a) aroundmaximum8 spectroscopic factor for the 22 state and the
1
and
+
200 above threshold which we identified as g.s.
0
He)p
reaction
which
is
described
with
three
states:
ground
the (p,
þ
0.000,
01 are de- allowed
0
The CCBA calc
1
The
neutron
energies,
E
,
relative
to
threshold
of values for the 31 state 1consistent with that
10 range
10 1.5 MeV. We also observena shoulder around 3 MeV. Given
1
data
state (red),
first excited data
(green), and second excited (blue) states.
calculations w
+
fined
as
the
centroid
of
the
single-particle
neutron
excita150 that the broad structure
tensor
as solid
givengray
in line
Table
I.calculation
around 6 MeV is related to the protonlimitThe
21
models
the acceptance cutoff. The solid black
optical potenti
-1
tionenergy
energy
minus
the
one-neutron
separation
energy,
E
cutoff and therefore not a real state, we concluded that
spectroscopic
factorsphase
ob0
line10excitation
denotes
the energies
sum of theand
three-,
five-,0 and seven-body
n The
100
coupled channe
the
around
3 MeV
is
a second
excited have
state.tained
– Sn, and
as such,
centroids
threshold
+shoulder
from
and from
shell-model
space
contributions,
whose functions,
respective(b)
breakup
energies
are noted.
+ due toabove
1= E
exc
(a)the LSF wave
in Ref. [48]. T
0
0
–
The1 presence
and the
two excited
-2–1
2 of the
50
The
line indicates
the physical background
due to reactions
of
–1
positive
values. The
dataposition
are shown
in Figure 1
for states
the 1/2are
calculations
using
the Warburton-Brown
(WBP)
interac10dotted
were
calculate
Er≈ 1.3 MeV (DWBA)
Er≈ 3.4 MeV(DWBA)
+
(b)
+
compatible
several
previous
reports
[7,8,23,24,26].
+ with
+ (blue)
the beam
with
the plastic
scintillator.
The
thin solid line
isused
the sum
2
1.766,
2
(black),
1/2
(red),
and
5/2
states
for
nuclei
from
tion
[25],
also
appear
in
Table
I;
this
interaction
was
in
1
1
global
nucleon
energies
as a3 first estimate
of the resonance
all0–2
contributions. The region around
the
threshold is shown in the
100
0Using these
1
6
þ
þ –2
helium
to oxygen
(Z 2= 2–8) having
N4 = 5, 7,5 8, 9, and
10, Ref. of[3]
10 to reproduce the 2
N
!
0
transition
data
for
internal
wave f
1
1
energies of the states,
a16fit
was performed employing “Voigt
inset.
EX ( one
C) (MeV)
each of which have only
neutron in the 1s0d shell. We several neutron-rich C isotopes. The present
data for the 57 shapes of the
L=0
–3
–3 L = 1
-1
show additional data for N = 11 and 13 (open symbols),
10
with the 8 identical to tho
three lowest
states in 16 C are in good agreement
034301-4
L=2
1
FIG. 1which
(colorthough
online).
(a)
Proton
energy
versus
position
9 suggesting that
þ
they
behave
in
a
remarkably
similar
manner,
WBP calculations.
The estimated
values
for the 22 and 3þ
Unbound
Bound
1
10 of the angular
(d) –4
–4 (c)
spectrum for the 15 Cðd; pÞ16 C reaction measured in
+ inverse
+(c)
-2
cannot be put on equal footing with the3.027,
data
deduced
from
0mm,
levels 10
are0 also5 consistent
with25shell-model
10
15
20
0
5
10 predictions.
15
20
25
30
2 02and z
kinematics
with
HELIOS.
The
target
is
at
z
¼
0
10N < 11 due to the additional neutrons in the 1s0d shell.
–4
–2
0
4 (deg)
3 4 5 6 7 8 use of the DWB
θc.m.
The strength
of 5/2
both
0þ2 θstates
in the2 ðd;
pÞ reaction
+
increases
in the beam direction. The different groups correspond
(deg)
cm
Z
16 C, shown
Forfinal
manystates
of theincases
in Figure 1,
the figure.
determina- indicates that eachEn has(MeV)
to different
as is indicated
on the
a substantial ð1s1=2 Þ2 component,
FIG.
4.
(Color
online)
Angular
distributions
for
the
ground
state
9
16
2
2
tion
of
the
neutron
excitation-energy
centroid
was
straightHeð0d
as meaFigure strong
2. (Top)
Missing-mass
(b) C excitation-energy spectrum.
Þ and
revealing
mixing
between spectrum
the
ð1s1=2for
9
5=2 Þ
tensor force
(a) and the two first
1He [(c) and (d)] compared to
dataexcited states of
8He
from neutron transfer data, an ideal probe of sin- configurations.
sured1 by the (d,p)
reaction
on
Angular
15 [8]. (Bottom)
WS calculation
Also,
while
in
Cblue)
theDWBA
1=2þcalculations.
ground
We present
L
=
0,
1,
2
(respectively
red,
green,
and
(d)
+ ++ +
gle-particle
states,
with
relative
spectroscopic-factor
and
distributions
corresponding
to
the
observed
strength,
sup3.986/4.088,
2
/3
2
/3
together with
(b)
Angular
distribution
of
the
g.s.
compared
to
CCBA
calculations.
100 with an estimated 5% systematic uncertainty
state may
80%,
2 21 1 from
0 be identified with the 1s
0 1=2 configuration, and
statistical weightings. In total, there are 19 sets of 1s1/2 and porting the assignments
made. These data were used for the
detector misalignment. The absolute cross-section scale
the 0.74 MeV 5=29þ state with the 0d5=2 one, in 16 C the
0d5/2 data, far more than the
limited information available s and
d
states
at
He,
the
only Z = 2 data point available in
�
2
was determined by using the 0 monitor detector as deð1s1=2 Þ –1configuration is dominant–1in the excited 0þ level.034301-5
on
the
0p
states.
Details
of
their
origins
are
given
in
Ref.
this
study.
See
Ref.
[8]
for
further details.
1/2
10
scribed above; the plotted uncertainties reflect only the
This result agrees qualitatively with those of Ref. [11],
[5].
Similar
compilations
have
been
made
over
the
years,
combined
statistical
uncertainties
from
the 50
data and
–2 the predicted configuration
–2 mixing between the
0
10 the most
20 recent
30 detailed
40one being
60 [7], although
N
in 1995
Monteperhaps
Carlo with
simulations.
The horizontal
bars represent
þ states is less than what is observed. Other calcu5
two
0
θ
(deg)
+
cm
discussing
the
trends
in
the
context
of
Coulomb
displacean unbound
1/2 state with missing-mass
energy 0.18 MeV,
(deg)
7
the angular range includedθin
each
data point. The angular
–3
–3
c.m.
[6,10] give even larger mixing; in Ref. [10]8 the
ment energies.
Since then,
a great deal more
datashow
has been lations
hence
S
=
–0.18
MeV,
and
the
lowest-lying
resonance
at
distributions
for the ground
and second-excited
states
n
9two
ð1s1=2
Þ2 MeV
is larger
in
the
ground state,
andit in
Ref.
[6]
theWhile
gathered.
We
highlight
two
recent
cases
here.
1.24
has
ℓ
=
1
character
making
the
p
state.
clear
‘
¼
0
character,
confirming
the
tentative
assignment
10
FIG. 2 (color online). Angular distributions for different tran1/2
–4
–4
configurations
carry
approximately
equal amplitudes.
The
tentative in the
work
of Ref. [8], combined
with previous
of J in
¼ 15
0þCðd;
[23]
state.
The firstsitions
pÞ16for
C. the
Thesecond-excited
curves represent
distorted-wave
–4
–2
0
2
4
observed
mixing
also
conflicts
with
the
conclusions
of
2
3
4
5
6
7
8the
9
+
measurements 5/2(summarized
in Figure 5 of Ref.
[8]),
excited
and Energy
the
presumed
doublet near
MeVusing
are
Born
approximation
calculations
described
in the4 text,
Hestate
Neutron
Centroids
2 and
Z
(MeV) state is dominantly ð1s
E n ground
Þ
Ref.
[2]
that
the
+
1=2
9
optical-model
parameters
Refs. nuclei
[27] (solid
line),possessing
[28]
5/2 state at 3.24 MeV was adopted as the d5/2 centroid.
consistentHe
with
‘ ¼of2.the from
is
one
most exotic
observed
(dashed
line),spectroscopic
[29] (dot-dashed
line),
and
[30] (dotted
line).
Relative
factors
were
obtained
by
a neutron-to-proton
ratio
of
3.5 and
having
nocomparbound
states. that the first-excited level is largely a single-neutron
) excitation. Our spectroscopic factor for the
The
uncertainties
are statistical
do extracted
not reflectfrom (1s1=2
5=2Centroids
ingcross-section
the
cross
sections
withand
distorted-wave
Theexperimental
single-neutron
centroids
of interest
were
N =0d10
þ excitation agrees with the strongly configuration-mixed
systematic
errors
in
the
absolute
scale,
as
described
in
the
text.
2
Born a approximation
calculations
done with the
code
recent neutron transfer
(d, p) measurement.
It was
carried 1
Centroid information for the 1s1/2 and 0d5/2 states was
PTOLEMY
Thewith
curves
in beam
Fig. 2inrepresent
calculations
functions
thenuclei
LSF and
shell-model
analyses.
16C and 18
out a[24].
GANIL
a 8He
inverse kinematics
and us- wave
available
for of
two
withWBP
N = 10,
O, based
The
measured
spectroscopic
factors,
excitation
energies,
done
with
four
sets
of
optical-model
parameters,
and
each
ing
the
MUST2
detector
setup
at
the
SPIRAL
ISOL
facility
on
single-neutron
transfer
data
and
the
fact
that
the 3+
our estimate of the uncertainties from the normalization
15
curve
was
normalized
to thethe
experimental
cross sections.
andstates
the energies
of theare
1s1=2
levels fromwhile
C
[8].
The
experimentally
determined
spectrum
in these nuclei
of aand
pure0dsd5=2configuration
and
the
variations
among
differentmissing-mass
parameter
sets.
2
The
deduced
spectroscopic
factors
are
listed
in
Table
I.
+ states
2 configurations.
þ
interaction
for
yield
matrix
elements
for the
ðsdÞ residualData
distributions
from
this
work
are
shown
in
Figthe
4
have
pure
d
for
the
forWhile and
the angular
2þ
and
3
states
could
not
be
resolved,
their
1
Because of 2The
the uncertainty
the absolute
cross
sections,
15C(d,
ignoring
sd-shell
neutrons
coupled
J ¼ 0þ . By
authors
havein
determined
thethe
ground
state is twomer
was acquired
recently
in atomeasurement
of the
relativeure 2.
contributions
could
be
estimatedthat
from
widths
the results were normalized by requiring the sum of the 0þ
orbital,
the
any
contributions
from
the
higher
lying
d
3=2
of the lower excitations (0.140 MeV FWHM) and the
spectroscopic factors to add up to 2.0. The values obtained
þ
2
i
¼
ð1s
Þ
wave
functions
may
be
written
as
j0
centroid of the doublet peak, 4.077(.005) MeV. The esti1=2 þ
1
with each of the four parameters sets were averaged to
2
þ
2
2
Þ
and
j0
i
¼
�ð1s
Þ
þ
ð0d
Þ
,
where
ð0d
mated
from 24, No. 5=2
maximum possible contribution to this doublet Vol.
4, 2014, Nuclear
Physics
1=2News17
5=2
2
obtain
þ the results in Table I. The errors are dominated by
2
2
the 22 state is 23%. This limit is used to derive the
þ ¼ 1. The two amplitudes and may then be
2501-2
6E exp – åE WS (MeV)
6E exp (MeV)
1forward
TABLE I. Experimental and theoretical spectroscopic factors for states in 16 C and 15 C from the 15 Cðd; pÞ16 C and 14 Cðd; pÞ15 C
reactions. The values labeled LSF and WBP correspond to those obtained from Ref. [18] and shell-model calculations with the WBP
interaction described in the text, respectively. Experimental uncertainties are in parentheses.
feature article
SICAL REVIEW LETTERS
energy versus
for p-16 C copond to differ-energy specFig. 1(b). The
M, determined
lution, energy
y spread of the
and the kineesolution was
þ þ
2 =31 doublet
of this peak is
citations.
d transitions in
hown in Fig. 2.
eometry of the
iency for the
calculated by
e transport in
measured field
was typically
0.000; 0+
P
EpE (MeV)
(MeV)
(a)
Counts/8 keV
were detected
IOS) [21,22].
y reactions in
ore, superconhe beam direc110 g=cm2
used. Protons
f-mass frame
etic field and
detector array
e target. The
’ energy, disl to the cyclo16 C ions were
ray of silicon5� –2.8� in the
ted in the upm intensity was
at 0� behind a
by a factor of
ator made this
d the shape of
ematic uncer-
tions for the states populated in that work [11]. The 18O
1
data come from normal kinematic data, in particular that
7
of Ref. [12]. However, because there are two neutrons in
1.766; 2+
6
1
the sd shell, the interaction energy between them must be
5
removed to extract the single-neutron energy comparable
3.027; 0+
2
to the odd-N data. A model independent method for apply+
3.986; 2
4
2
ing this correction is to deduce the interaction from one set
4.088; 3+
3
1
of N = 10 centroids and apply the correction to the other
resulting in a single N = 10 data point. The interaction
2
energies (two-body matrix elements) extracted for 18O in
1
Ref. [12] were therefore applied to the centroid energies of
16C. Combining the corrected energies, 3.49(20) MeV for
0
-400
-350
-300
-250
-200
-150
-100
-50
0
week ending
+ state
P H Y S I C A L R E V the
IEW
LET
T E4.49(20)
RS
Z (mm)
3+ state
and
MeV for the 424
(from the
SEPTEMBER
2010
PRL 105, 132501 (2010) z (mm)
250
(t,p) reaction data of Ref. [13]), with an Sn value of 4.25
+ +
þ
and the
maximum
spectroscopic
(b)
22 /31+ +(a)
MeV
[14] results
in the datafactor
for thefor
1s the
and220dstate
5/2 energies
200
0 1 01
þ 1/2
0.000,
16
range
ofallowed
Figure 1
for ofC.values for the 31 state consistent with that
10
+
150
limit as given in Table I.
21
The excitation energies and spectroscopic factors ob100
+
tained from the LSF wave functions, and from shell-model
1
+
The Role of Finite Binding
01
02
50
calculations using the Warburton-Brown (WBP) interac+ +(b)
A simple question to ask is to what extent is the sepa21 21
1.766,
tion [25], also appear in Table I; this interaction was used in
driven by the effects of
ration
of the s1/2 and d5/2 orbitals
100
0
1
2
3
4
5
6
Ref. [3] to reproduce
the 2þ
! 0þ
data for
1 states
1in transition
16
finite
binding?
The
behavior
of
a finite potential
EX ( C) (MeV)
several neutron-rich C isotopes. The present data for the
had been studied before16by many; for instance, Bohr and
three lowest states in C are in good agreement with the
1
Mottelson considered the behavior of neutron orbits
in a þ
FIG. 1 (color online). (a) Proton energy versus position
WBP calculations. The estimated values for the 2þ
15
16
2 and 31
spectrum for the Cðd; pÞ C reaction measured in
static
nuclear
potential
for
heavier
systems
[15],
remarking
+ inverse
(c)
+
3.027,
levels are also consistent with shell-model
predictions.
2 02and z
kinematics
with HELIOS. The target is at z ¼
00
mm,
on the s states, which approach
the threshold much more
10
The strength of both 0þ states in the ðd; pÞ reaction
increases in the beam direction. The different groups correspond
slowly than other states. In this vain, the role of2 this proxindicates that each has a substantial ð1s1=2 Þ component,
to different final states in 16 C, as is indicated on the figure.
imity to the neutron threshold was explored
by
explicitly 2
(b) 16 C excitation-energy spectrum.
Þ2 and ð0d5=2
revealing
strong
mixing
between
thestates
ð1s1=2calculated
comparing
the
data
to
the
equivalent
in Þ
1
15
þ
configurations.
Also,
while
in
C
the
1=2
ground
a Woods-Saxon potential with standard parameters (e.g.,
+ ++ +(d)
3.986/4.088,
2 2 /3 1 from
22 /3
100 with an estimated 5% systematic
configuration,
may be identified
the4.03
1s1=2
80%,
uncertainty
1
rstate
fm,with
VSO =
MeV)
[5]. For eachand
0 = 1.25 fm, a = 0.63
þ
state of
with
0d5=2 one, potential
in 16 C the
the 0.74 MeV
5=2
detector misalignment. The absolute cross-section scale
individual
isotope
the depth
thethe
Woods-Saxon
2
was determined by using the 0� monitor detector as deÞ configuration
is dominant
in the excited
0þ level.
ð1s1=2
was
varied
until the calculated
single-neutron
energy
re10 above; the plotted uncertainties reflect only the
scribed
This result
those of Ref.
[11],
produced
the agrees
bindingqualitatively
energy of thewith
experimentally
known
combined
statistical
uncertainties
from
the 50
data and
although
the
predicted
configuration
mixing
between
the
0
10
20
30
40
60
0d
orbital.
The
spin-orbit
parameters
were
fixed
such
5/2
Monte Carlo simulations. The horizontal bars represent
+what
+isenergy
17
states is less
than
observed.
Other
calcutwothey
0þ reproduced
that
the
1/2
5/2
splitting
in
O.
θ
cm (deg)
(deg)
the angular range includedθin
each
data point. The angular
c.m.
lations
[6,10]
give1seven
larger mixing; in Ref. [10] the
The
energy
of the
1/2 orbital was then deduced within
distributions
fortop
theplot
ground
andthe
second-excited
show
2
Figure 3. The
shows
characteristicstates
proton
en- the
ð1ssame
is larger inThe
theexperimental
ground state,energy
and in difference
Ref. [6] the
two
be1=2 Þ potential.
clear
‘(color
¼ 0 online).
character,
confirming
the as
tentative
assignment
FIG.
Angular
distributions
for different
ergy2 versus
target-detection
distance
recorded
usingtranthe tween
configurations
carry
approximately
equal
amplitudes.
The
,
is
shown
in
Figure 4a,
with
the
the
two
states,
ΔE
þ
exp
of
J in
¼ 15
0spectrometer
[23]
for
second-excited
state.
The correfirstsitions
Cðd;
pÞ16
C. the
The
curves
represent
HELIOS
[9,10]
at ATLAS.
Thedistorted-wave
lines
observed
mixinga fit
also
withfrom
the the
conclusions
red
line showing
thatconflicts
was derived
computed of
Born
approximation
calculations
described
in
the
text,
using
excited
state
and
the
presumed
doublet
near
4
MeV
are
15
2 and
spond to states populated in the C(d,p) reaction [11]. The values
Ref.
[2]
that
the
ground
state
is
dominantly
ð1s
for
only
those
nuclei
with
N
less
than
10.
One
1=2 Þimoptical-model
parameters
from Refs. [27] (solid line), [28]
consistent
with
‘ ¼ 2. distributions
corresponding
angular
are shown below. The mediately
that the
calculated
difference
describes
that the notices
first-excited
level
is largely
a single-neutron
(dashed
line),spectroscopic
[29] (dot-dashed
line),
[30] (dotted
line).
Relative
factors
wereand
obtained
by
comparextraction
of theuncertainties
s- and d-state
centroid
forand
thisdo
N not
= 10
sys- remarkably
well
the
gross
trend
between
experimental
en-the
0d
)
excitation.
Our
spectroscopic
factor
for
(1s
The
cross-section
are
statistical
reflect
1=2
5=2
ing the experimental cross sections with distorted-wave
tem is discussed
inthe
theabsolute
text. scale, as described in the text. ergy
þ
systematic
errors
in
differences
as
a
function
of
neutron
binding,
even
for
21 excitation agrees with the strongly configuration-mixed
Born approximation calculations done with the code
the
N
=
11
and
13
isotones.
This
is
a
strong
suggestion
that
wave functions of the LSF and WBP shell-model analyses.
PTOLEMY [24]. The curves in Fig. 2 represent calculations
finite
binding
playsspectroscopic
a dominant role
in the
trends ofenergies,
these
The
measured
factors,
excitation
done
with
four
sets
of
optical-model
parameters,
and
each
our estimate of the uncertainties from the normalization
p)
reaction
carried
out
at
Argonne
National
Laboratory
states.
curve
normalized
to thethe
experimental
cross sections.
and the energies of the 1s1=2 and 0d5=2 levels from 15 C
and
thewas
variations
among
different parameter
sets.
2
in inverse
kinematics
using
the
ATLAS
accelerator,
with
To explore
this further,
can subtract
outinteraction
the effectsfor
The
deduced
spectroscopic
factors
are
listed
in
Table
I.
residual
yield
matrix elements
for one
the ðsdÞ
While
the 2þ
and 3þ
states could not be resolved, their
1 in-flight
15C produced
þ the s state.
the
technique,
thesections,
HELIOS that
appear
to
be
due
to
the
finite
binding
of
Because
of 2thevia
uncertainty
in the
absoluteand
cross
two sd-shell neutrons coupled to J ¼ 0 . By ignoring
relative contributions could be estimated from the widths
spectrometer
[9,normalized
10]. Figure 3
shows thethe
angular
the
results were
by requiring
sum ofdistributhe 0þ
shows thisfrom
subtraction
of the
experimental
dif-the
any contributions
the higher
lying
d3=2 orbital,
of the lower excitations (0.140 MeV FWHM) and the Figure 4b
spectroscopic factors to add up to 2.0. The values obtained
þ
wave functions may be written as j01 i ¼ ð1s1=2 Þ2 þ
centroid of the doublet peak, 4.077(.005) MeV. The estiwith each of the four parameters sets were averaged to
2
2
ð0d5=2 Þ2 and j0þ
mated maximum possible contribution to this doublet from
2 i ¼ �ð1s1=2 Þ þ ð0d5=2 Þ , where
obtain
the
results
in
Table
I.
The
errors
are
dominated
by
þ
2
2
1822 state is 23%.
Nuclear
Physics
News,
the
This limit
is used
to Vol.
derive24,
theNo. 4,
þ ¼ 1. The two amplitudes and may then be
2014
8
dσ/dΩ
(mb/sr)
dσ/dΩ
(mb/sr)
on in inverse
T1=2 ¼ 2:45 s)
AS at Argonne
produced by
100 p nA 14 C
The resulting
d an energy of
y of 16.4 MeV,
The intensity
week ending
24 SEPTEMBER 2010
132501-2
TABLE I. Experimental and theoretical spectroscopic factors for states in 16 C and 15 C from the 15 Cðd; pÞ16 C and 14 Cðd; pÞ15 C
reactions. The values labeled LSF and WBP correspond to those obtained from Ref. [18] and shell-model calculations with the WBP
interaction described in the text, respectively. Experimental uncertainties are in parentheses.
+
E n1/2
+
– E n5/2
(MeV)
6E exp – ∆E WS (MeV)
dσ/dΩ
(mb/sr)
dσ/dΩ
(mb/sr)
Co
40
he experimental
to the spin-parities o
energy approximation (WBEA) where the 9 He internal wave
2
µg/cm targets
30
8
functions were calculated by binding the neutron to the He
as spectroscopic fact
spectra obtained
20
feature article
complex remnant term
core with a standard Woods-Saxon potential with reduced
ss m4 in Eq. (1)
10 r0 = 1.25 fm, and diffusivity a0 = 0.65 fm, the well
either post- or prior-fo
radius
ron rest masses.
Since the inciden
0
0
-2
-1
0
1
2
3
4 week
5 ending
6
7
) is
dA-50
here
as
ErV
17
L ferences
RE
I
E
W
L
E
T
T
E
R
S
3-bothat
E [MeV]
influence
-body 7-bo24
2010
from the calculated differences. Note
O 5described
the Woods-Saxon
potential calculations
as of deuteron
dby
dy
y SEPTEMBER
E (MeV)
e.
1
lies at zero due to the10spin-orbit
parameters chosen and shown in Figure 4, with the ordering (s orbital test
moving
bethis we performed
.S.systematically
(DWBA)
G.Sd. orbital)
(CCBA) implicit in the sign change of ΔE . The
imatelythe
200
N =keV
11 and 13 data pointsGlie
higher, by low the
þ
exp
FIG. spectroscopic
3. (Color online) Experimental
missing
mass
spectrum
for
(CCBA) calculation f
state
andfor the
factor
the
22effects
a smallmaximum
amount, as a 8result
of the extra neutrons
in for
binding
energy
account
the over 4 MeV change
(a) onlyaround
d another
+
He)p
reaction
which
is
described
with
three
states:
ground
the
(p,
þ
0
CCBA
calculation
the 1s0d shell.
Naively,
difference
of differences
must 3 instate
the differences
betweenwith
the s and
across
Z=
1d, 0
thatd orbitalsThe
range
of values
for the
10this
3 1MeV.
Givenallowed
1 second
1
1consistent
data
state
(red),
first
excited
(green),
states.
highlight effects not
related
to finite
binding.
Onedata
sees that and
2–8, while theexcited
action of(blue)
the tensor
force,
for example,
only
calculations with the
limit
as solid
given
inareline
Table
I.calculation
ted to the
the proton
remaining
deviations
from zero
on average
an order
accounts for
a smallThe
fraction
the tensor
total energy change.
The
gray
models
the acceptance
cutoff.
solidofblack
optical potential was
-1
of magnitude
thanenergies
the experimental
Shell-model
calculations
have been
remarkably successful
e concluded
that smaller
The
excitation
spectroscopic
factors
ob0 MeV)the
line10(~0.5
denotes
sum
of theand
three-,
five-,0 and
seven-body
phase
changes (over 4 MeV) over the sampled range. These re- in describing these features also, but one notescoupled
that the ef-channels (CD
nd excited
state.tained
from
thesame
LSF
wave
and
from
shell-model
space
whose
respective
breakup
energies
are
maining contributions
are contributions,
of(a)
the
direction
andfunctions,
mag- fects(b)
of
the binding
energy
willnoted.
be inherently in
included
Ref. in[48]. The nece
xcited states
-2
The
dotted
line
indicates
the
physical
background
due
to
reactions
of
–1
–1
nitude asare
those
expected
from
the
monopole
component
the
effective
interactions
used.
Other
approaches
may
also
calculations
using
the Warburton-Brown (WBP)
interac10
werethose
calculated using
≈ 1.3 MeV (DWBA)
Er≈ 3.4 MeV(DWBA)
+ +(b) of the tensor force [16]—theEshaded
r
region
in
Figure 4b
be
successful
in
describing
these
data;
for
example,
,23,24,26].
the beam
with
the plastic
scintillator.
The
thin solid line
isused
the sum
, 21 highlights this.
tion [25],
also
appear
in Table
I; this
interaction
was
in
1
global nucleon optical
that the
treatthreshold
deformationisexplicitly,
or include
of5 the resonance
of all0–2
contributions. The region around
shown in
the coupling to the
6
þ
þ
–2
continuum.
10 to reproduce the 2
[3]
1 ! 01 transition data for N internal wave function
mploying “VoigtRef. inset.
This near-threshold effect must play a role
5 in the reducshapes of the L = 0
several neutron-rich C isotopes. tion
The
present
data
forgapthe
L=0
of
the
traditional
N
=
8
shell
being
7that the neutron
–3
–3 L = 1
Impact of s State Behavior
-1
16
11Be. to those for
identical
orbital
at, for8example,
states move
below the p1/2
10
agreement
with
the
three lowest
states in C are in sgood
034301-4
L
=
2
position
In this case, however, theþmonopole þ
part 9
of the
tensor in- that the infl
Single-Neutron Ordering
suggesting
WBP
calculations.
The
estimated
values
for
the
2
and
3
Unbound
Bound
2
1
teraction
is
expected
to
be
larger,
about
the
same
of
The
behavior
of
the
sd
neutron
orbitals
in
the
light
10
(c)
(d)
–4
–4
+n inverse
of order
the angular
distribu
+(c)
-2
magnitude
as
the
binding
energy
effects.
neutron-rich
nuclei
presented
in
Figure 1
can
be
reliably
10
, 02and z
levels are0 also5 consistent
with25shell-model
10
15
20
0
5
10 predictions.
15
20
25
30
2m,
use
of
the
DWBA
to i
–4
–2
0
2
4 (deg)
2 3 4 5 6 7 8
þ
θc.m.
The
strength
of
both
0
states
in
the
ðd;
pÞ
reaction
+
orrespond
θcm (deg)
Z
E n5/2 (MeV)
he figure.
indicates that each has a substantial ð1s1=2 Þ2 component,
FIG. 4. (Color online) Angular distributions for the ground state
6E exp – åE WS (MeV)
6E exp (MeV)
2
Þ2 (d)]
and
ð0dforce
revealing
strong mixing
between the ð1s and
5=2 Þ to
tensor
compared
(a) and
1 the two first
dataexcited states of 91He [(c)1=2
15
WS calculation
configurations.
Also,
while
in and
Cblue)
theDWBA
1=2þcalculations.
ground
We present the 9 H
L = 0, 1, 2 (respectively
red, green,
+ +(d)
+
/3
together with all pub
Angular
distribution of
the g.s.
to CCBA calculations.
2
and
state(b)may
with
thecompared
1s0 1=2 configuration,
nty
0 be identified
1 1 from
on scale
the 0.74 MeV 5=2þ state with the 0d5=2 one, in 16 C the
or as deð1s1=2 Þ2–1configuration is dominant–1in the excited 0þ level.034301-5
only the
This result agrees qualitatively with those of Ref. [11],
data
and
–2 the predicted configuration
–2 mixing between the
although
0
60
N
represent
þ
5
two 0 states is less than what is observed. Other calcu7
e angular
–3
lations –3[6,10] give even larger mixing;
in Ref. [10]8 the
ates show
ð1s1=2 Þ2 is larger in the ground state, and in Ref. [6] the 9two
signment
10
erent tran–4
–4
configurations
carry
approximately
equal
amplitudes.
The
The
firstorted-wave
–2
0
2
4
observed –4mixing
also
conflicts
with2 the
3 conclusions
4 5 6 7 8of
MeV
are
ext, using
5/2+ (MeV)
2
Z
E
Ref. [2] that then ground state is dominantly ð1s
1=2 Þ and
ine), [28]
+ states (red), ΔE , as a function of the energy of the 5/2+
Figure 4. (a)
The difference
in energy between the
1/2+ and
that
the first-excited
level
is5/2largely
a single-neutron
exp
tted
line).
comparrelative to threshold as determined from the experimental data. The curve state is a fit to calculations of the energy differ) excitation.
Ourreproduces
spectroscopic
factor for
(1s1=2 0d5=2
not reflect
ted-wave
ence using Woods-Saxon
potentials.
The general trend
that of the experimental
data. the
The N = 11 and 13 data
þ
points
were
not
included
in
the
calculations,
although
the
experimental
data
are
added
here.
(b)
The difference between
nhethecode
text.
21 excitation agrees with the strongly configuration-mixed
the experimental
and calculated differences as a means of showing what is not accounted for by the effects of finite bindculations
wave
functions
of theusing
LSF
andinteractions,
WBP shell-model
analyses.
ing. The orange
shaded
region, calculated
different
shows the possible
contribution of the tensor force
on
the
d
orbital.
The measured spectroscopic factors, excitation energies,
and each
malization
sections.
and the energies of the 1s1=2 and 0d5=2 levels from 15 C
eter
sets.
2 2014, Nuclear Physics News19
Table
I.
No. 4,
residual interaction for
yield matrix elements forVol.
the24,
ðsdÞ
ved,
their
sections,
two sd-shell neutrons coupled to J ¼ 0þ . By ignoring
he widths
of the 0þ
any contributions from the higher lying d3=2 orbital, the
and the
obtained
2
wave functions may be written as j0þ
The esti1 i ¼ ð1s1=2 Þ þ
raged to
2
þ
2
2
feature article
Summary
A detailed study of data on the 1s1/2 and 0d5/2 states in
light neutron-rich nuclei, greatly aided by recent studies
with radioactive ion beams at facilities around the world,
emphasizes a notable trend in the separation of these orbitals. Over a relatively small range of neutron excess, between isotopes of He and O, the states diverge by over 4
MeV. It has been shown that a significant fraction of this
deviation can be attributed to the behavior of the neutron
s state near threshold, with the action of the tensor force
playing only a small role. While the former has been discussed before, an explicit comparison to the experimental
data, much of which is new, is revealing. It is tempting to
surmise that this effect plays a significant role in the breakdown of the N = 8 shell gap, but matters are complicated
somewhat by the overlap between the p1/2 neutrons and pshell protons. Such behavior also leads one to speculate the
existence of halo states in heavier systems, with the 78Ni
region being most tantalizing.
Detailed spectroscopic information, such as that presented in the measurements discussed above, allows one
to elucidate specific aspects of nuclear structure that may
otherwise be masked. It is highly likely that the wealth of
data already available in this region will be added to significantly in the near future, as well as the first glimpses of
20
N = 51 data
0
N = 51 calculation
–1
–2
En (MeV)
Neutron Halo Nuclei
The lingering of the neutron s state at the neutron
threshold is the same phenomenon responsible for the
halo states in weakly bound light systems such as in 11Li
and 11Be [3]. Two other neutron-rich regions of the chart,
where the higher lying s orbitals may appear sufficiently
close to threshold, are just outside N = 50 around 78Ni
and outside N = 126 below 208Pb. As shown in Figure 5,
Woods-Saxon potential calculations qualitatively describe
similar features as those present in the quite limited experimental data sets around 78Ni, showing hints that the
2s1/2 orbital may “dip” below the 1d5/2 orbital close to
the threshold. The large uncertainty in the experimental
one-neutron separation energy in 79Ni lends itself to the
possibility of a neutron halo in this nucleus. In addition,
nuclei with smaller Z, such as the neutron-rich Ca isotopes
highlighted in recent theoretical work [17], may also form
halos. Far more exploratory work is needed to understand
how well a neutron-halo is defined in such large systems
as those around N = 126; however, the strong influence of
finite binding on the neutron s state in the weakly bound
systems is clear.
–3
–4
1/2+
1/2+
–5
–6
5/2+
5/2+
–7
–8
28
32
36
Z
40
44
4.7 4.9 5.1 5.3 5.5 5.7
RV (fm)
Figure 5. (Left) The energy of the 1/2+ and 5/2+ orbitals
outside N = 50. The solid data points are from single-nucleon transfer on the stable isotones [18], while the empty
data points are from transfer with radioactive ion beams
[19] or other probes. The grey data point represents the
binding energy of 79Ni [14]. (Right) For illustrative purposes we show Woods-Saxon calculations of the energy of
the same states as a function of the radius of the potential,
using the prescription described in the text (except fixing
the spin-orbit parameters to 91Zr).
data on heavier nuclei exhibiting the identified threshold
characteristics.
Acknowledgments
This material is based on work supported by the U.S.
Department of Energy, Office of Science, Office of Nuclear
Physics, under Contract Number DE-AC02-06CH11357.
This research used resources of ANL’s ATLAS facility,
which is a DOE Office of Science User Facility.
References
1. R. V. F. Janssens, Nature 459 (2009) 1069.
2. I. Talmi and I. Unna, Phys. Rev. Lett. 4 (1960) 469.
3. I. Tanihata et al., Prog. Part. Nucl. Phys. 68 (2013) 215.
4. M. Freer, Nature 487 (2012) 309.
5. C. R. Hoffman et al., Phys. Rev. C 89 (2014) 061305.
6. T. Aumann and H. Simon, Nucl. Phys. News 24 (2014) 5.
7. H. T. Fortune, Phys. Rev. C 52 (1995) 2261.
feature article
8. T. Al Kalanee et al., Phys. Rev. C 88 (2013) 034301.
9. J. C. Lighthall et al., Nucl. Instrum. Methods A622 (2010) 97.
10. B. B. Back and A. H. Wuosmaa, Nucl. Phys. News 23 (2013)
21.
11. A. H. Wuosmaa et al., Phys. Rev. Lett. 105 (2010) 132501.
12. T. K. Li et al., Phys. Rev. C 13 (1976) 55.
13. H. T. Fortune et al., Phys. Lett. B70 (1977) 408 and D. P.
Balamuth et al., Nucl. Phys. A290 (1977) 65.
14. G. Audi et al., Chin. Phys. C 36 (2012) 1287.
15. A. Bohr and B. R. Mottelson, Nuclear Structure (W. A. Benjamin, Inc., New York, 1969), Vol. 1, 240.
16. T. Otsuka et al., Phys. Rev. Lett. 95 (2005) 232502.
17. G. Hagen et al., Phys. Rev. Lett. 111 (2013) 132501.
18. D. K. Sharp et al., Phys. Rev. C 87 (2013) 014312.
19. J. S. Thomas et al., Phys. Rev. C 76 (2007) 044302.
Calem R. Hoffman
Benjamin P. Kay
Filler?
facilities and methods
Light Exotic Nuclei at JINR: ACCULINNA and
ACCULINNA-2 Facilities
Joint Institute for Nuclear
Research (JINR)
JINR is an international scientific
centre covering a broad range of activities in the nuclear, particle, theoretical physics, and biophysics. It is
located in Dubna, 130 km to the north
of Moscow. The JINR Laboratory Portrait can be found in a recent Nuclear
Physics News article [1].
Radioactive Ion Beam Studies at
FLNR
Flerov Laboratory of Nuclear Reactions (FLNR) is a JINR subdivision,
most famous for the super-heavy element program. Through the last few
years new elements with atomic numbers Z = 114–118 were discovered
here in the study performed jointly
with the three U.S. research centers
(Lawrence Livermore National Laboratory, Oak Ridge National Laboratory, and Vanderbilt University). Two
of these new elements are recognized officially by IUPAC and have
got their names: 114Flerovium and
115Livermorium. FLNR possesses two
high-current cyclotrons: the U-400
(3–30 A MeV heavy-ion beams) used
mainly for the heavy element study
and U-400M (higher energy, 6–60 A
MeV beams). The latter machine has
broader research objectives including the radioactive ion beam (RIB)
program implemented at the ACCULINNA fragment separator.
tron-rich RIBs. It has a compact and
comparatively simplistic design with a
14 m long achromatic stage, containing a wedge degrader in its dispersive
focus, and a 8.5 m ToF stage providing particle-by-particle identification
of the RIB (Figure 1). Finally, the
beam is transferred into the low-background target hall (Figure 2). Despite
its modest size the facility gains on
the high-intensity primary beams of
the U-400M cyclotron. The obtained
RIB energies of 20–40 A MeV fit well
direct reaction studies. Lower-energy
and stopped beam experiments are
feasible as well. The ACCULINNA
beam line hosts installations used by
the JINR Laboratory of Radiation Biology and by the material radiation
studies carried out for the Russian
Federal Agency RosCosmos.
Available Instruments
The ACCULINNA group develops
or participates in the development of
a broad range of detector arrays required for the low-energy nuclear-reaction studies (Figure 3).
Various types of high-granularity
detector telescopes are manufactured
and used depending on the kinematical
conditions of experiment. Previously
our group used a subset of the neutron
detector array DEMON. Now an array
of 32 stilbene scintillation detectors
(each crystal being 5 cm thick and 8
cm in diameter) is developed and currently available. The GADAST targetarea γ-detector array consisting of 64
CsI(Tl) and 16 LaBr3(Cr) modules
was built by the ACCULINNA group
within the program of infrastructure
upgrade for the FRS facility at GSI.
The GADAST array can also be available for ACCULINNA experiments.
The ACCULINNA group participates in the development OTPC technology. The idea of time-projection
chamber with optical readout was promoted by the group of Warsaw Uni-
ACCULINNA
Facility Layout
The ACCULINNA fragment separator (http://aculina.jinr.ru) was initially aimed for the study of light neu-
22
Figure 1. Layouts of the ACCULINNA and constructed ACCULINNA-2 facilities
in the U-400M cyclotron hall.
Figure 2. View of ACCULINNA low-background target hall with (from left to right) reaction chamber, DAQ, and neutron
array DEMON. People in protective suits prepare the tritium gas system to operation. Cryogenic tritium cell with doubleshielding.
versity led by Professor M. Pfützner.
It provided in the recent years very
important results on rare decay modes,
which include the first measurements
of momentum distributions inherent
to the 2p radioactive decay and discovery of the beta-delayed 3p emission (in 45Fe and 31Ar). The camera
R&D and tests are partly conducted in
Dubna and the observation of rare de-
cays for light exotic nuclei 8He, 14Be,
27S were performed at ACCULINNA.
The ACCULINNA group has tradition of using cryogenic gas/liquid
targets for reaction studies. Most in-
Figure 3. Some instrumentation available at ACCULINNA. Opened reaction chamber view, charged particle telescopes,
stilbene neutron detector array, GADAST γ-detector array, and Warsaw OTPC.
teresting is a massive instrumentation
connected with the cryogenic tritium
target (Figure 2). Tritium target opens
additional opportunities for achieving
extreme neutron-rich nuclear systems
and detailed studies of their excitations (also discussed below). The use
of gas/liquid targets allows low-background experiments with low-intensity
(≥103 pps) secondary beams. Technically, the use of pure (not chemically
confined) tritium is a great challenge
and subject of serious security regulations. The special conditions of work
with tritium, according to the national
security standards, allow the use of
“free” (gas, liquid, or solid) tritium for
research only in a few laboratories in
the world. One of few such laboratories in Russia is the All-Russian Research Institute of Experimental Physics (Sarov). The technical base for the
gas/liquid tritium target operation was
successfully developed in JINR since
the mid 1990s in close collaboration
and with a leading role of colleagues
24
from Sarov. This collaboration is a
nice example of the conversion of
military technology for the benefit of
fundamental science.
Scientific Ideology
The current period in the RIB research is marked with massive upgrade and construction of new facilities all over the world. The “new
generation” RIB factory at RIKEN is
operating for several years and such
upgrades as FAIR, FRIB, and SPIRAL-2 are actively promoted and will
define the tomorrow of the research
in this field. What should be the place
of the minor facilities? Our vision is
that important opportunities and competitive scientific programs can be
provided by minor facilities if one focuses on a narrow research field.
For the ACCULINNA group such
a field of choice is associated with
direct reactions with exotic beams
leading to the population of particleunstable states in the nuclear systems
located near and beyond the driplines. The relatively low-energy RIBs
(~20–40 MeV/nucleon) are suitable
for the production of exotic nuclei in
few-nucleon transfer reactions, which
are well-understood due to their clear
mechanism. Compared to the fragmentation and knockout reactions occurring at higher energies (~70–500
A MeV), which become increasingly
popular at the modern RIB factories,
the “old school” transfer-reaction approach supplies additional prospects.
Figure 4 gives some qualitative illustration that the initial state (and consequently the reaction mechanism)
contributions should be different in
the “high-energy” and “low-energy”
approaches.
The study of few-body decays
makes a special field of interest for our
group. Few-body dynamics is widespread in the drip-line systems due to
paring interaction. In certain conditions it gives rise to exclusive quantum mechanical phenomena. Among
Figure 4. Population of “superheavy” He isotopes in high-energy reactions by
particle (cluster) removal reactions (red) and at lower energies by the transfer
reactions (blue).
these, the most known are the Borromean type of three-body halo systems
and two-proton radioactivity. Notions
of such a phenomenon as two-neutron
and even four-neutron radioactivity
were recently promoted and some
two-neutron emitters beyond the neutron drip line are now investigated at
the leading RIB facilities. Compared
with the two-body decays, where internal properties of the decaying system come to light only via the resonance position and width, the decays
with emission of few particles also
provide access to information encoded
in the correlations among the decay
products. This field is not well investigated now and opens broad opportunities for pioneering research.
As a special approach, not broadly
developed elsewhere, we promote
correlation studies in continuum as a
spectroscopic tool. For example, the
angular distributions of the products
in the direct reactions are a standard
basis for spin-parity identification.
Less widespread but very powerful
alternative method here relies on the
usage of induced by the transfer reaction mechanism strong alignment
of products (particle-unstable states).
The powerful methods developed by
our group for the three-body decays of
aligned states were so far not applied
elsewhere.
Recent Experiments
Below we give examples of some
key experiments of the last decade
underlying opportunities connected
with correlation studies of continuum
decay of exotic nuclei. These results
are based on the following physical
peculiarity of the transfer reactions:
the single-step reaction mechanism
imposes strong restrictions on the angular momentum transfer. Namely,
only zero projection of the angular
momentum can be transferred in the
frame associated with the transferred
momentum. As a result, for the total
momenta J > 1/2 strongly aligned
states are typically populated. The
strong alignment of the whole system
produces expressed angular correlation pattern for the emitted fragments
in the transferred momentum frame.
The 5H produced in the 3H(t, p) reaction [2]. This was the pilot experiment aimed for the three-body decay
of broad aligned states. The feature
to be emphasized here is the opportunity to disentangle the contribution of
very poorly populated 5H g.s. from the
strong background of the higher-lying
states, where it is otherwise completely lost (Figure 5). The most notable examples of further application
of this technique include spin-parity
identification in the spectra of 9He [3]
and 10He [4] produced in the (d, p) and
(t, p) reactions. For 10He this allowed
us to demonstrate that shell structure
breakdown, known so far for 12Be,
also extends further in the N = 8 isotone (Figure 6).
The mentioned examples portray
the results obtained exclusively utilizing “technologies” available at
our group. However, the research interests are not limited by these and
close cases. In recent years we have
obtained a number of results on structure, decay dynamics, and rare decay
modes of relatively light nuclei from
4H to 26S using variety of methods
like transfer, charge-exchange, and
QFS reactions (http://aculina.jinr.ru/
publications.php).
Collaboration
Local Experiments
Usually ACCULINNA has around
2 months of beam time per year and
hosts on average 1–2 guest experiments. These are mainly experiments
performed by other Flerov lab groups
and groups from JINR member states.
It is expected that the new facility ACCULINNA-2 will operate as “user facility” with easy access for users from
outside.
External Experimental Programs
The members of our group are involved in experimental works on the
RIB study at GSI, GANIL, RIKEN,
and MSU.
There is a broad program of collaboration with the FRS group of
GSI. The ACCULINNA group participated in works on the hardware
development for the FRS and future
SuperFRS facilities. These activities
are now concentrated on the EXPERT
setup initiative for SuperFRS@FAIR
(http://aculina.jinr.ru/pdf/topic8_
expert.pdf). The FAIR-Russia Research Centre foundation supports
now a team of young scientists working on the FAIR-related projects
within our group.
Figure 5. Excitation spectrum of 5H and angular correlations of 3H fragment
in the system of transferred momentum. Dots show data and histogram provide
Monte-Carlo results. The 1/2+ g.s. contribution at about 1.9 MeV is practically
invisible on the thick “background” of the higher-lying states. Only correlation
analysis allows extracting this information.
Figure 6. Anomalous level ordering demonstrated for 10He indicate the shell
structure breakdown known in 12Be extends also further to the most neutron-rich
part of N = 8 isotone.
26
ACCULINNA-2 Project Status
The research program of the ACCULINNA facility was recognized
as successful and prospective. To enforce this program a major upgrade
of the facility was initiated in 2008.
This resulted in the construction of
a new fragment separator, ACCULINNA-2. This facility should deliver
the RIBs produced by means of 35–60
A MeV primary heavy-ion beams with
atomic numbers 3 ≤ Z ≤ 36. The ACCULINNA-2 design is optimized for
larger RIB intensities and for highprecision studies of direct reactions
leading to the population of nuclear
systems near and beyond the drip lines
having in mind sophisticated correlation experiments.
At the moment the manufacture
of the ACCULINNA-2 components
by the ion-optics solution provider
SigmaPhi (Vames, France) is in the
final stage. Construction work has
started in the U-400M hall. The installation should be completed by the end
of 2014, and we plan the commissioning and first experiments running in
2015.
To provide broader experimental
opportunities the auxiliary “massive”
instrumentation should be delivered
together with the separator “body.”
The ACCULINNA group is working
now on the development and financing options for several of the most
important items. (i) The zero-angle
spectrometer (“sweeper magnet”) is
required for a number of experiments,
where heavy reaction products go
forward close to the secondary beam
direction. This option becomes important in experimental conditions
with intense or strongly contaminated
secondary beams (>>105 pps). (ii) The
ion optics of the ToF stage of ACCULINNA-2 is optimized to accommodate an RF-kicker. This option is essential for purifying secondary beams
on the proton-rich side. (iii) The cryogenic tritium target gas system is one
of the really unique opportunities provided at FLNR. Unfortunately, the existing system is “bound” to its physical location by certification conditions
concerning hazardous radioactive
substances. The advanced next-generation tritium system is planned to be
constructed in the ACCULINNA-2
target area.
Having the ACCULINNA-2 separator fully put into operation the
Flerov lab will convert the presentday ACCULINNA for biophysics and
applied studies.
Welcome
The operation of the new ACCULINNA-2 fragment separator since
2015 at the Flerov Laboratory of JINR
will open new opportunities for scientific collaboration with JINR in the
field of RIB research. The research
program of ACCULINNA-2 for the
first years of operation is not yet finalized, and we welcome new ideas and
experimental proposals for the arriving facility.
Acknowledgments
This work was supported by the
Russian Foundation for Basic Research 14-02-00090a grant. Leonid
Grigorenko acknowledges the support
of the Russian Ministry of Education
and Science NSh--932.2014.2 grant.
Leonid Grigorenko
Flerov Laboratory of Nuclear
Reactions, Joint Institute for Nuclear
Research, Dubna, Russia, and
Natinal Research Center "Kurchatov
Institute", Moscow, Russia
References
1. B. Starchenko and Y. Shimanskaya,
Nuclear Physics News 22 Phys. Rev. C
(2012) 7.
2. M. S. Golovkov et al., Phys. Rev. C 72
(2005) 064612.
3. M.S. Golovkov et al., Phys. Rev. C 76
(2007) 021605(R).
4. S. I. Sidorchuk et al., Phys. Rev. Lett.
108 (2012) 202502.
Andrey Fomichev
Research, Dubna, Russia
Gurgen Ter-Akopian
Research, Dubna, Russia
Nuclear Physics at Jožef Stefan Institute
The Jožef Stefan Institute (Institut
“Jožef Stefan”) was founded by the
Slovenian Academy of Sciences and
Arts in 1949 as the Physics Institute
for Nuclear Research. In 1952 it was
renamed in honor of the Slovenian
physicist Jožef Stefan (1835–1893),
mostly known today for the law describing the energy flux of blackbody radiation as a function of temperature,
j = σT 4,
which is named after him and his student Ludwig Boltzmann. The Stefan’s
constant σ has been immortalized in
the institute’s logo (Figure 1), which
represents the letters I, J, and S in
the International Telegraph Alphabet,
while also resembling the letter σ.
After its early stages of a dedicated
nuclear physics facility, the institute’s
research became quite diversified. Although it still remains the country’s
only national physics institute, its
almost one thousand staff members
work in the fields of physics, chemistry, computer science, robotics, materials research, and biochemistry. The
institute is heavily involved in the educational process since more than two
hundred of its members are also Ph.D.
students. Currently the largest departments at the institute are the Condensed Matter Physics Department
and the Environmental Sciences Department. The institute’s infrastructure
Figure 1. The logo of Jožef Stefan Institute.
28
Figure 2. The research reactor TRIGA of the Jožef Stefan Institute.
includes a research reactor TRIGA
Mark II (Figure 2), that recently celebrated its 40th anniversary of continued operation.
Nuclear physics research is currently performed only at the Department of Low and Medium Energy
Physics. During the last decade the
department has consisted of about
40 staff members and their work can
roughly be divided into three groups:
atomic physics, environmental radioactivity measurements, and a relatively small group performing basic
and applied nuclear physics research.
The atomic physics group operates
and utilizes the department’s own 2
MV tandetron accelerator built by
High Voltage Engineering Europa
B.V. (Figure 3). The accelerator is
equipped with three ion sources that
enable it to accelerate many different
ion beams, from very intense proton
beams from a multicusp ion source,
specialized duoplasmatron source for
low consumption 3He beams, to various light- and heavy-ion beams from
the sputtering source. The main advantage of the accelerator is its stable
operation that enables us to obtain
high-quality ion beams.
The research at the accelerator is
conducted at four beam-lines (Figure 4), where various ion-beam analysis techniques are applied. One beamline is devoted to particle-induced
X-ray analysis (PIXE) in air. This
technique is mainly used in archeometry to study cultural heritage objects
that cannot be placed in vacuum. The
second beam-line is the micro-beamline, where the PIXE technique is
applied with ion beams with a diameter of less than one micrometer. The
state-of-the-art at this beam-line is
the MeV-range secondary ion-mass
Figure 3. The 2 MV tandetron accelerator at the Jožef Stefan Institute.
spectrometry (i.e., SIMS with an
MeV-range ion beam), where the distribution of large organic molecules in
biological samples can be studied with
great precision.
The third beam-line is devoted
to nuclear reaction analysis (NRA)
and elastic recoil detection analysis
(ERDA) methods. These two methods are mainly used for depth profiling of hydrogen isotopes in materials
exposed to tokamak plasma within
the European Fusion Development
Agreement. The rightmost beam-line
in Figure 4 is usually connected to a
special scattering chamber for highresolution X-ray spectroscopy. However, this scattering chamber has often
been traveling to various European
synchrotrons, where synchrotron radiation is used instead of protons to
achieve high resolution in X-ray spectroscopy. The accelerator belongs to
the SPIRIT network through which
outside users can apply for beam time
and, if successful, have all their expenses covered.
Many of the environmental radioactivity measurements are performed
in our High Resolution γ-ray Spectrometry Laboratory. The laboratory is market-oriented and measures
activities of γ-ray emitting isotopes
in samples collected in the environ-
ment. Many samples come from the
vicinity of the only Slovenian nuclear
power plant at Krško. The laboratory
cooperates with the Comprehensive
Nuclear-Test-Ban Treaty Organization
and the International Atomic Energy
Agency. Supplementing high resolution γ-ray spectrometry is the Liquid
Scintillation Spectrometry Laboratory
in which activities of tritium in water
with extremely low detection limits
are measured, as well as 14C components in biodiesel fuels. This laboratory is compliant with the European
Commission Council Directive 98/83/
EC on measuring gross α/β emitters
in drinking water and will already
be prepared once Slovenia implements it in its own legislation. We also
have a secondary standard laboratory
that maintains the national reference
standard for absorbed and equivalent
doses of gamma radiation. Our calibration and measurement capabilities
are being loaded into the database
of Bureau International des Poids et
Mesures.
In spite of being the smallest group
at the Department, its Nuclear Physics
Group conducts research in three different but closely related fields. We are
members of two major international
collaborations, Hall A at Thomas Jefferson National Accelerator Facility
(TJNAF or Jefferson Lab), Newport
News, VA, USA and the A1 Collaboration at the Mainz Microtron MAMI,
hosted at the Institute of Nuclear
Physics of the Johannes-Gutenberg
University, Mainz, Germany. In both
of these research centers, we are actively involved in designing, planning,
and conducting of electron scattering
experiments, as well as their calibrations and subsequent data analyses.
At MAMI we are primarily involved in all experiments devoted to
pion electro-production on protons,
both near the production threshold (test of low-energy theorems
of chiral perturbation theory in the
neutral-pion channel, extractions of
the axial form factor of the proton in
the charged-pion channel) and in the
nucleon resonance region (determination of electric and Coulomb quadrupole contributions to the Delta (1232)
excitation, studies of the N(1440)
(Roper) resonance); many of these
experiments, running at the standard
three-spectrometer setup of the A1
Collaboration, exploit polarization
degrees of freedom (polarized beam,
proton recoil polarimetry) in order to
amplify the appropriate physics sensitivities. A large fraction of our recent
efforts, however, was directed at the
newly implemented KAOS spectrom-
Figure 4. The four beam-lines of the tandetron accelerator at the Jožef Stefan
Institute.
eter, in particular in its primary role
in the physics studies of hypernuclei,
for which we have designed and built
an aerogel Cherenkov counter. We are
also involved in virtual Compton scattering experiments at low momentum
transfers, the main goal of which are
the generalized polarizabilities of the
proton (the extensions of the usual
static electric and magnetic polarizabilities to virtual photons); a part of
this program was also conducted by
using polarized beam and/or focalplane proton polarimetry (single-spin
and double-spin asymmetries). The
group has also collaborated in benchmark determinations of electric and
magnetic elastic form-factors of the
proton as well as measurements of
neutron electric form-factor at high
momentum transfer. Our involvement
at MAMI further extends to dark photon searches and exploiting the initialstate radiation method to access proton elastic form-factors at extremely
30
low momentum transfers not accessible directly; the latter effort is closely
related to the “proton radius puzzle”
that has been permeating the field for
the past several years.
At Jefferson Lab our primary involvement in the past five years or so
has been in the so-called BigFamily of
experiments comprising, among others, a set of measurements utilizing the
large-acceptance (approximately 100
msr) spectrometer BigBite in addition
to the standard two high-resolution
spectrometers of Hall A, together with
a polarized beam and a high-density,
optically pumped polarized 3He target.
Our main focus was the measurement
of electron-target double-polarization
asymmetries (in-plane target polarization) in deuteron, proton, and neutron
knockout from 3He in the quasi-elastic
region, a set of processes that constitute an extremely sensitive probe of
spin and isospin structure of the 3He
nucleus and its dynamics, but a large
part of our collaboration extended to
studies of single-spin inclusive as well
as exclusive asymmetries (neutron
knockout) when the target was polarized out of plane. All these experiments have been devised to test the
most precise available theories of fewnucleon systems, in particular regarding the question whether, or to which
accuracy, the polarized 3He nucleus
may be regarded as an effective polarized neutron target.
Meson electro-production in the
first, second, and third nucleon resonance region, both in the non-strange
and strange sector, is also the subject
of our theoretical investigations, in
which we exploit various chiral quark
models of the nucleons, in particular
those with explicit non-quark degrees
of freedom (i.e., those that incorporate
meson-cloud effects). In these studies
we collaborate with the co-workers
from the institute’s Theoretical Physics Department. In the past few years
we have calculated the meson electro-production multipole amplitudes
(both the electro-magnetic vertex and
the strong decay, including the appropriate complex phases) for all major
(positive and negative parity) nucleon
resonances up to an energy of about
1.8 GeV in a coupled-channel framework that can accommodate any underlying quark model to compute its
matrix elements.
Some nuclear physics research is
also performed at our tandetron accelerator. We are especially interested in
nuclear astrophysics, more precisely
in the role of electron screening in
nuclear reactions at low energies. We
have confirmed the previous suggestion that the accepted static picture of
electron screening inadequately describes the process. This is especially
evident in experiments on implanted
hydrogen in metallic targets, where
many measured values of the electron screening potential in different
nuclear reactions are more than an order of magnitude above the adiabatic
limit inferred from the static picture.
To figure out which dynamic process
is responsible for the large electron
screening, we are trying to deduce the
dependence of the electron screening
potential on the proton number Z
of the reactants. Previous measurements have failed to confirm the expected linear dependence. We also
observed that the strength of electron
screening depends on the position of
the hydrogen nuclei in the metallic
lattice.
We are also active in radiation detector development with activities in
novel materials for neutron detection.
We are developing new algorithms
for digital pulse processing, where
our focus is in pulse shape analysis
for separating neutron and γ-ray signals. However, our main specialty is
the development of novel algorithms
for high count rate spectroscopy from
both scintillator and semiconductor
detectors.
Thanks to two Slovenian high tech
companies, Instrumentation Technologies and Cosylab, Slovenia became
a founding member of FAIR GmbH
in Darmstadt, Germany. Since this
membership is such a promising opportunity, the Slovenian scientific
community and in particular the Nuclear Physics Group at Jožef Stefan
Institute are turning toward FAIRrelated research. We are especially
interested in the NUSTAR collaboration, where our expertise in pulse
processing at high count rates might
prove useful.
To conclude, the nuclear physics
group at the Jožef Stefan Institute is
small but young and very much alive
and kicking. In June 2015 we are organizing together with our Croatian
colleagues the next one in the international conference series Nuclear
Structure and Dynamics.
Matej Lipoglavšek
Jožef Stefan Institute,
Ljubljana, Slovenia
Simon Širca
Faculty of Mathematics and Physics
University of Ljubljana,
Ljubljana, Slovenia
Filler?
impact and applications
Cosmic Rays: Hurdles on the Road to Mars
Space radiation has long been recognized as a major health hazard for
human space exploration. Unlike terrestrial radiation, space radiation comprises high energy protons and high
charge and energy (HZE) nuclei, which
produce distinct forms of biological
damage to biomolecules, cells, and tissue compared to terrestrial radiation,
making risk predictions highly uncertain [1]. While the crews in low Earth
orbit (LEO), such as the International
Space Station (ISS), are partially protected by the Earth’s magnetic field, for
interplanetary missions in deep space
the risk of acute effects caused by solar
particle events (SPE) and late effects
induced by protons and HZE nuclei in
the galactic cosmic rays (GCR) is significant. Intense SPE can be lethal for
unprotected crews, but shielding is effective against solar protons. Chronic
exposure to GCR represents instead a
very serious risk of carcinogenesis [2].
It is not clear if the health risks associated with long-term exposure to HZE
nuclei can be adequately estimated by
epidemiological studies, as done for radiation protection on Earth, due to both
quantitative and qualitative differences
in biological damage. Therefore, risk
estimates, mostly based on groundbased cell or animal studies, are affected by large uncertainties. Moreover, shielding from very energetic
CGR nuclei tends to be poor given the
weight constraints of spacecraft.
In 2006, the National Council on
Radiation Protection and Measurements (NCRP) concluded that no recommendations for specific radiation
protection limits could be provided to
NASA regarding long-term exploratory-class missions, because of the
high uncertainty associated with the
risk of late effects [3]. Since that report, many new developments demand
a re-analysis of the problem:
32
Figure 1. Sand dunes and rocks around the “Dingo gap” on Mars. The photograph was taken by the Curiosity rover, which landed on Mars on 6 August 2012,
following a 253-day, 560-million-kilometer space trip. The Curiosity rover, with
the Radiation Assessment Detector (RAD) mounted to its top deck, was inside the
Mars Science Laboratory spacecraft. RAD measured the space radiation doses
during the cruise in deep space [5] and on the Mars surface [6]. Image Credit:
NASA/JPL-Caltech/MSSS.
1. The one-year mission to the ISS
(2015) and the Mars mission (Inspiration Mars, 2018) are now
scheduled, and all exploration
scenarios foresee a long permanence of humans in space.
2. NASA implemented a radiation
protection standard that limits
astronauts’ exposure in LEO to
a 3% risk of exposure-induced
death (REID) within the 95%
confidence interval (CI), and
uses a specific model for the
REID calculation in different
mission scenarios [4].
3. The Mars Science Laboratory
(MSL), carrying the Curiosity
rover (Figure 1), measured for
the first time the radiation field
on the route to Mars [5] and on
the planet’s surface [6], supporting previous estimates and
demonstrating that radiation
dose rates in space are indeed
200–400 times higher than on
Earth.
4. New ground-based radiobiology
experiments at high-energy particle accelerators, supported by
NASA at the Brookhaven National Laboratory (Upton, NY,
USA) and by ESA at the GSI
Helmholtz Center (Darmstadt,
Germany), show that, in addition
to cancer [2], HZE nuclei can
induce late tissue degenerative
effects, especially CNS damage
and cardiovascular diseases.
Based on these new data, is it acceptable to plan long-term ISS missions and planetary exploration? What
are the scientific and ethical issues?
Radiation Limits
General public and professionally
exposed workers are subject to specific radiation dose limits set by law.
Although current recommendations
are risk-informed, they are not based
directly on assumed limits on risk and
do not directly account for uncertainties in estimates of risk associated with
given doses. For example, the dose
limits recommended by the International Commission on Radiological
Protection for the public is set to 1
mSv/year, while for radiation workers it is 20 mSv/year [7]. Emergency
exposures (generally up to 100 mSv)
are permissible in case of nuclear accidents, as it happened in the Fukushima
nuclear power plant disaster in 2011.
Higher doses (around 1 Sv) may only
be justified if they involve the saving
of human lives. A simple dose-limit
approach is also implemented by the
Russian and European Space Agencies, with an astronaut’s career limit
set at 1 Sv, independently of the age at
exposure and sex [1].
In contrast, the radiation protection
standard for astronauts currently used
by NASA is expressed directly in terms
of a limit on risk of lifetime exposureinduced mortality, and include the uncertainty on the risk estimate: 3% REID
at 95% upper CI [4]. This approach has
not been applied to the general public
or Earth based worker, where dose limits are preferred for practical reasons,
but it is clearly more scientific and appropriate for a small group of workers
such as the astronauts, and of growing
interest on Earth [8]. In fact, the exposure limits and risk model are generally considered prudent, appropriate,
and scientifically sound, and they were
positively evaluated by the National
Research Council [9].
However, by applying these standards many exploratory missions
would exceed the limits. In Figure 2,
estimates using the NASA model [4,
10]. for four space missions are compared to terrestrial exposures, including the 1-Sv career limit used by the
Russian and European space agency,
where the uncertainty is calculated us-
Figure 2. Estimates of cancer mortality risk and 95% CI for four different
space mission scenarios compared with terrestrial exposures. Estimates are for
a 45-year-old, male, never-smoker. Estimates for Mars asteroid mission, Mars
opposition-class mission, and the Mars Design Reference Mission (DRM) proposed by NASA are assumed in a solar minimum and are detailed in Ref. [4].
Details of the ISS missions are in Ref. [10]. Annual dose for a radiation worker
is assumed to be 20 mSv and 100 mSv for an emergency exposure (acute) [7]. Estimates of the excess cancer mortality risk for a 1-Sv dose limit are also reported,
assuming terrestrial exposure [11].
ing the U.S. Environmental Protection
Agency model [11]. The estimates in
Figure 2 are for a 45 year old, male,
never-smoker, and include the risk for
late cardiovascular effects. The lower
background cancer rates of a neversmoker population reduce radiation
risk estimates compared to estimates
for the U.S. average population. Moreover, risk estimates will be higher
for females and younger astronauts.
Even for the ISS, missions longer than
1-year may exceed the current guidelines for astronauts involved in multiple missions, depending on age, sex,
and mission duration [10]. The fixed
career dose limit at 1-Sv limit adopted
by the Russian and European Space
agencies have not received external review; however, they would far exceed
the NASA guidelines, even assuming
the uncertainty level of terrestrial exposures [11].
Ethical Issues
The high risk predicted for many
missions may push toward simple solutions, such as an ease of the dose
limits and the adoption of “informed
consent” strategies. However, these
approaches pose serious ethical and legal concerns. On Earth, in addition to
the dose limits, the regulatory agencies
adopt the so-called ALARA principle,
which means that all unjustified exposures should be avoided and all measures should be taken to keep the exposures as-low-as-reasonably-achievable
[7]. A recent report from the Institute
of Medicine recommends several ethics principles should be applied to the
NASA health standards for decisions
regarding long-duration and exploration spaceflights [12]. NASA should
systematically assess risks and benefits
and the uncertainties attached to each,
drawing on the totality of available
scientific evidence, and ensure that
benefits sufficiently outweigh risks. In
any case, the principle of “avoid harm”
should be applied, which implies that
NASA should minimize the risks to
astronauts from long-duration and ex-
ploration spaceflights and address uncertainties through approaches to risk
prevention and mitigation that incorporate safety margins. These recommendations are of course of general value,
and should therefore be considered by
all space agencies, which can potentially be engaged in long-duration and
exploratory missions. ESA is indeed
currently supporting several modeling
and experimental research programs in
space radiation protection. An international effort would be extremely useful
in this respect, to avoid astronauts from
different countries being subject to different standards, which is intrinsically
an ethical problem. From our viewpoint, it is only upon the completion
of a significant fraction of the scientific
studies that can be reasonably suggested to reduce uncertainties and develop mitigation measures, that space
agencies can argue they have made a
significant effort. At this time, perhaps
higher levels of space radiation risk
could be accepted, while at the same
time consistency with the many efforts
to reduce the much lower risks from
flight failures, which are now estimated at less than 1 in 250, would have
been demonstrated.
Scientific Issues
Reducing uncertainty is clearly the
highest priority for understanding the
risk of exploratory missions. Recent
evidence of tissue degenerative effects has led to further increasing the
risk estimates [4], previously based
on cancer risk alone [3]. High priority
should therefore be given to radiobiology research on cancer and non-cancer
effects induced by HZE particles in
accelerator-based experiments. Even
though very much has been learned in
the past 10 years, the translation of in
vitro or animal experiments to human
protection remains problematic if the
mechanisms are not well understood.
Estimates in Figure 2 suggest that,
even with a reduced uncertainty, exploration will hardly be possible without
appropriate countermeasures both in
34
the near future (applying the ethical
standards recommended by the Institute of Medicine [12]) and especially
in the medium-term future, when
spaceflight will be extended to a much
larger fraction of the population (space
tourism, workers on planetary bases).
At the moment, biomedical countermeasures (radioprotective drugs or dietary supplements) have only limited
efficacy, and it is not expected that they
will solve the problem [2]. Crew selection for radiation resistance may become more likely as knowledge is increased, however possibly constrained
by the small pool of candidates and
other selection criteria. Passive shielding also has limited effects, because of
the severe weight constraints in space
flight, yet the use of light, highly hydrogenated materials is a simple and
effective way for reducing risk [13],
and in situ material can be exploited
for safe shielding in planetary bases.
Active shielding (e.g., the use of a
magnetic field similar to the Earth’s
protection of the Van Allen belts), is
very promising but technically immature, and probably will not be realistic for the next 10–20 years. Mission
design can gain large factors. Moving
the missions to solar maximum drastically reduces the GCR dose (by up to
50%), even though the risk of intense
SPE is higher. Reducing the transit
time is clearly the best solution, both
for minimizing radiation exposure and
for the other medical issues caused by
microgravity and isolation. This can be
achieved by innovative propulsion systems and choice of appropriate flight
windows. In any case, the recent MSL
data [5, 6] confirm that cosmic rays
are high hurdles on the way to Mars,
and an international effort is clearly urgently needed to address the problem.
Experts in medicine and space radiation will gather at the Ettore Majorana
Foundation in Erice in October, in the
framework of the International School
on Heavy Ions, to discuss this issue
and hopefully to produce a consensus
document to be implemented by the
space agencies [14].
References
1. M. Durante and F. A. Cucinotta. Rev
Mod Phys. 83 (2011) 1245.
2. M. Durante and F. A. Cucinotta. Nat
Rev Cancer. 8 (2008) 465.
3. NCRP. Information Needed to Make
Radiation Protection Recommendations for Space Missions beyond LowEarth Orbit. NCRP Report No. 150,
Bethesda, MD, 2006.
4. F. A. Cucinotta, M. H. Kim, L. J. Chappell, and J. L. Huff. PLoS One. 8
(2013) e74988.
5. C. Zeitlin, D. M. Hassler, F. A. Cucinotta, et al.. Science. 340 (2013) 1080.
6. D. M. Hassler, C. Zeitlin, R. F. Wimmer-Schweingruber, et al. Science.
343 (2014) 1244797.
7. ICRP. Recommendations of the International Commission on Radiological Protection. ICRP Publication No.
103, Ann. ICRP 37(2–4), Elsevier,
NY, 2007.
8. J. Preston, J. D. Boice, A. B. Brill, et
al. J. Radiol. Prot. 33 (2013) 573.
9. National Research Council. Technical Evaluation of the NASA Model
for Cancer Risk to Astronauts Due to
Space Radiation (The National Academies Press, Washington, DC, 2013).
10. F. A. Cucinotta. PLoS One. 9 (2014)
e96099.
11. D. J. Pawel. Health Phys. 104 (2013)
26.
12. Institute of Medicine. Health Standards for Long Duration and Exploration Spaceflight: Ethics Principles, Responsibilities, and Decision
Framework (The National Academies
Press, Washington, DC, 2014).
13. M. Durante. Life Sci. Space Res. 1
(2014) 2.
14. International School on Heavy Ions,
III Course on: Hadrons in Therapy
and Space, Erice, Italy, 1–4 October 2014. Frontiers in Oncology, in
press. http://journal.frontiersin.org/
ResearchTopic/3520
Marco Durante
GSI Helmholtz Center for
Heavy Ion Research and Darmstadt
University of Technology
Darmstadt, Germany
Francis A. Cucinotta
University of Nevada,
Las Vegas, Nevada, USA
meeting report
The First International African Symposium on Exotic
Nuclei (IASEN2013)
The first International African
Symposium on Exotic Nuclei (IASEN-2013) was held on 1–6 December 2013, not far from Cape Town
(Republic of South Africa). This Symposium was organized by two scientific centers—the iThemba Laboratory
for Accelerator-Based Sciences, South
Africa and the Joint Institute for Nuclear Research, Russia.
The symposium grew out of the 6th
Symposium on Exotic Nuclei (EXON
2012), which was held in Vladivostok, Russia, when the then director of
iThemba LABS, Zeblon Vilakazi, had
an idea to organize a similar conference in South Africa. This idea was
supported during a round table discussion by almost all leading participants
of the symposium. IASEN-2013,
similar to the EXON symposia, was
devoted to the investigation of nuclei
in extreme states; the following topics
were discussed: exotic nuclei and their
properties, shell structure, collectivity,
rare processes and decays, nuclear
astrophysics, applications of exotic
beams in material research, and present and future facilities.
The first African Symposium was
attended by 140 scientists from 16
countries and 42 institutions. A school
for young participants and students
from several SA universities, where
leading scientists gave lectures, was
organized the day before the opening of the Symposium. Thomas Auf
der Heyde, deputy director-general
of the Department for Science and
Technology of South Africa, officially
opened the symposium; in his detailed
report he presented the perspectives
of nuclear physics and technology in
South Africa. He was followed by reports of progress and plans at facilities
around the world: R. Bark (iThemba
LABS), M. Thoenissen (MSU), M.
Lewitowicz (SPIRAL 2, GANIL), K.
Johnston (ISOLDE/CERN), H. En’yo
(RIKEN), R. Tribble (Texas A&M),
F. Weissbach (GSI/FAIR), S. Galés
(ELI-NP), A. Popeko (JINR/DRIBs3),
R Kruecken (TRIUMF), and G. de
Angelis (SPES/INFN).
At the end of the Symposium, a
discussion of cooperation between
South African research centers with
the world’s leading laboratories was
organized. A joint memorandum of
cooperation was adopted that endorsed a proposal by iThemba LABS
for an ISOL based radioactive beam
facility in South Africa.
The last day of the symposium was
marked with a minute’s silence for the
loss of a world leader—Nelson Rolihlahla Mandela.
Z. Vilakazi and Yu. Penionzhkevich
Co-Сhairmen of IASEN2013
AQ1
Filler?
news and views
Nuclear Physics Research Opportunities in Brazil
Research in nuclear physics in
Brazil is strong and well-recognized
internationally. There are researchers
in several Brazilian states, with most
of them confined to the Rio–São Paulo
axis. Historically, since the early
1950s, these researchers were stationed in universities such as the Universidade de São Paulo (USP), and the
Centro Brasileiro de Pesquisas Físicas
(CBPF), in Rio de Janeiro. A quite active program in experimental nuclear
physics was in place at USP, which
produced precise results on inelastic
scattering data such as the (d, p), (d.n)
reactions. This effort was enhanced
by the installation of the 8 MV Pelletron Accelerator Laboratory, which
entered into operation in 1970. The
realm of heavy ion physics was then
made available to Brazilian nuclear
physicists and several international
collaborations were put into place.
It allowed the study of light and medium heavy-ion reactions at low energies. Among these we mention charge
exchange reactions, which aimed to
probe isospin symmetry breaking,
fusion, and breakup reactions. Three
decades later the study of the physics
of neutron rich and proton rich nuclei
became possible through the installation of a twin solenoid system coupled
to the 8 MV Pelletron, baptized by the
name RIBRAS. This system has been
in operation since 2003 and reactions
with 6He and 8He were extensively
studied. In the electron accelerator effort, I mention the ongoing effort in
the construction of a MICROTRON,
also at the University of São Paulo.
Applied nuclear physics has also
been a strong area of activity in Brazil. Medical applications, 14C dating,
AMS use for dating and other applications in material science, and reactor physics have been under intense
36
investigation by the Brazilian nuclear
scientists. Many international collaborations in these areas are in course
and being intensified. Research opportunities in the AMS program are
currently enhanced through the installation of a state of the art apparatus at
the Universidade Federal Fluminense
(UFF) in Rio.
Research in nuclear theory has
been strong in Brazil over many decades. Very active groups working on
the many facets of the nuclear theory
(high spin states, giant resonances in
stable and exotic nuclei, multi-phonon
excitation of giant resonances), and
especially reaction theory are considered leaders in the field. Low energy
reaction theory and relativist heavyion reaction theory using hydrodynamical models are in the frontline of
physics. Hadron physics and relativistic description of nuclear structure
and reactions are also actively researched. Application of nuclear techniques to atomic and molecular physics (Bose-Einstein Condensation, one
and multi-phonon excitation in metal
and atomic clusters), as well as to
nanophysics and mesoscopic systems
(quantum dots, grapheme) have been
actively studied. Last, but not least,
research in nuclear astrophysics has
been pursued both theoretically and
experimentally in collaboration with
colleagues in Europe and the United
States. A group on nuclear astrophysics has been formed at the Institute for
Advanced Studies of the University of
São Paulo, which includes among its
members several of these colleagues
(see www.iea.usp.br/pesquisa/grupos/
astrofisica-nuclear/integrantes).
The interaction between the theorists and the experimentalists in all the
above areas has been of fundamental
importance in advancing the research
of both. It resulted in several widely
used models and concepts; to cite a
few we mention the São Paulo Optical
Model Potential (SPP), the Breakup
Threshold Anomaly (BTA), and the
Universal Fusion Function (UFF).
The nuclear physics community
holds annual meetings during the
first and second weeks of September
with the participation of several invitees from overseas. This has been
a tradition since the 1970s. Several
international topical meetings are also
organized almost every one or two
years. The community hosted and still
hosts imported international meetings, such as the INPC in 1989, and
the NN2006 and the Few-Body Conference in 2006. In these conferences,
hundreds of international participants
attended and helped in the success of
the events.
The international collaboration
is greatly valued by the Brazilian
nuclear physics community. Several
important research centers and laboratories have had an important role
in making these collaborations a success. Among these are: GSI, MIT,
Harvard, LHC, RHIC, MSU, Yale,
Madison, Texas A&M, Notre Dame,
Berkeley, Ganil, ULB, and Surrey, to
cite a few. Current opportunities for
the continuation of these collaborations have been bolstered through
the establishment by the Brazilian
federal government of the program
Science Without Borders, which
enables undergraduates and beginning graduate students to spend six
months in universities in Europe and
the United States to get familiar with
the teaching programs and research.
These visits are fully supported by
the federal funding agency CNPq (see
www.cnpq.br). Further, the program
supports the visit of senior academics
news and views
and researchers from oversees universities to visit one of the research
universities in Brazil for up to three
months or more, also well and fully
supported by the CNPq. It is hoped
that our international colleagues will
be encouraged to get in touch with
the contact persons listed below and
inquire about postdoc positions in
Brazil and senior scientists visits. I
should mention that for postdoc positions and visits to São Paulo, the State
Funding Agency, FAPESP (see www.
fapesp.br) has the means to support
postdocs for a period of two years,
renewable for one or two more years,
and one year visits by senior scientists
renewable for one more year.
Contact Persons
Alika Lepine Szily ([email protected])
Experimental nuclear physics, Pelletron and RIBRAS, Microtron,
nuclear astrophysics
Paulo R. S. Gomes (paulogom@if.
uff.br)
Applied nuclear physics, AMS, experimental nuclear physics
It is hoped that the above account
of the nuclear physics research currently done in Brazil will give a clear
picture of what our community is pursuing to enhance the knowledge in
our field and will encourage further
intensification of the already quite
healthy international collaboration.
Yogiro Hama ([email protected])
Relativistic heavy ion reaction theory,
Hadron Physics, LHC, RHIC
Mahir S. Hussein ([email protected])
Theoretical nuclear physics, low energy reaction theory, heavy ion reactions, nuclear astrophysics
Mahir S. Hussein
Instituto de Estudos Avançados,
Universidade de São Paulo,
São Paulo, Brasil
2012–2014 European Nuclear Physics
Dissertation Award
The board of the European Physical Society (EPS) Nuclear Physics
Division calls for nominations for the
2012–2014 European Nuclear Physics
Dissertation Award. The award recognizes the excellency of a recent Ph.D.
in Nuclear Physics. Nominations are
open to any person who has received
a Ph.D. degree in experimental, theoretical, or applied nuclear physics
in a country that is a member of the
EPS and where the degree has been
awarded within the three-year period
1 January 2012–31 December 2014.
The deadline for applications is 1 January 2015.
Nominations, which should be
made via the Dissertation Prize website
(http://www.eps.org/?NPD_prizes_
PhD), should include details of the
nominee, an electronic copy of the
Ph.D. Diploma showing the date it
was awarded, a 4–5 page summary
of the Dissertation/Thesis written in
English, an electronic copy of the Thesis, a copy of any publication directly
related to the candidate’s Ph.D. studies, a letter of support (max. 2 pages)
from the candidate’s thesis advisor,
and two additional letters of support
(max. 1 page each) from physicists
who are familiar with the candidate
and the research.
The prize winner will be given a diploma from the EPS, offered a plenary
talk at the 2015 European Nuclear
Physics Conference, 31 August–4
September, Groningen, The Netherlands, and 1000 € to cover their conference travel and subsistence costs.
Douglas MacGregor
Chair,
EPS Nuclear Physics Division
news and views
IBA-Europhysics Prize 2015 for Applied Nuclear Science
and Nuclear Methods in Medicine
Call for Nominations
The board of the European Physical Society (EPS) Nuclear Physics
Division calls for nominations for the
2015 IBA-Europhysics prize sponsored by the IBA company, Belgium.
The award will be made to one or several individuals for outstanding contributions to Applied Nuclear Science
and Nuclear Methods and Nuclear Researches in Medicine.
The board welcomes proposals that
represent the breadth and strength of
Applied Nuclear Science and Nuclear
Methods in Medicine in Europe.
Nominations forms, available on
the IBA prize website (http://www.
eps.org/?NPD_prizes_IBA), should
be accompanied by a brief CV of the
nominee(s) and a list of relevant publications. Up to two letters of support
from authorities in the field, outlining
the importance of the work, would
also be helpful. Nominations will be
treated in confidence and, although
they will be acknowledged, there will
be no further communication. Nominations should be submitted by e-mail
38
to Douglas MacGregor, Chair, IBA
Prize Committee:
[email protected].
uk
The deadline for the submission of
the proposals is 16 January 2015.
Prize Rules
1. The Prize shall be awarded every
two years.
2. The Prize shall consist of a Diploma of the EPS and a total prize
money of 5000 € (to be shared if
more than one laureate).
3. The money for the prize is provided by the IBA company.
4. The Prize shall be awarded to one
or more researchers.
5. The Prize shall be awarded without restrictions of nationality, sex,
race, or religion.
6. Only work that has been published in refereed journals can be
considered in the proposals for
candidates to the prize.
7. The NPB shall request nominations to the Prize from experts
in Nuclear Science and related
fields who are not members of the
Board.
8. Self-nominations for the award
shall not be accepted.
9. Nominations shall be reviewed
by a Prize Committee appointed
by the board. The Committee
shall consider each of the eligible
nominations and shall make recommendations to the board, taking also into account reports of
referees who are not members of
the board.
10. The final recommendation of the
board and a report shall be submitted for ratification to the Executive Committee of the EPS.
Douglas MacGregor
Chair,
EPS Nuclear Physics Division
in memoriam
In Memoriam: George Dracoulis (1944–2014)
George Dracoulis
Professor George Dracoulis, a pillar
of the Australian National University’s
Department of Nuclear Physics and a
highly respected researcher internationally, passed away on 19 June 2014,
after a brief battle with an aggressive
kidney cancer.
Born in Melbourne, Australia, to
Greek immigrant parents, George
graduated from the University of Melbourne with a Ph.D. in nuclear physics
in 1970. His thesis research involved
particle spectroscopy, but it was during
his three years as a research associate
at the University of Manchester, UK,
that he began the gamma-ray spectroscopy investigations that dominated
his research career. In 1973, he joined
the Australian National University
as a Research Fellow in the Department of Nuclear Physics, where the
world’s largest tandem Van de Graaff
heavy-ion accelerator was under construction. George played an integral
role in the accelerator’s development
and worked tirelessly to build up the
laboratory’s research infrastructure
and exploit it to perform world-class
research. He was appointed to a Chair
in Physics in 1991 and became Head
of Department in 1992, a position he
held until he retired in 2009.
The great contributions that George
made to the Department helped establish it as one of the world’s most respected nuclear physics laboratories.
He was renowned for the thoroughness of his experimental approach and
it was his clever use of isomeric states
as a sensitive probe that underpinned
many of his important contributions to
our understanding of nuclear phenomena. George demonstrated the key role
of octupole vibrations in the trans-lead
region and showed how the inclusion
of particle-vibration coupling is essential to reproduce the state energies and isomeric transition strengths,
while his substantial body of research
on high-K isomers and associated rotational structures gave profound insight
into both the purity of the K quantum
number and the nature of nuclear pairing. His clever alternative approach to
experimental problems is amply demonstrated by his identification of characteristic isomers in neutron-deficient
lead nuclei that can only occur at different nuclear shapes, providing some
of the best experimental evidence for
nuclear shape coexistence.
An excellent public speaker, George
was in high demand to give after dinner and summary talks at international
conferences, and was known for his
urbane manner and fondness for red
wine, good food, fine jazz and interesting conversation. He was the recipient
of numerous awards, being a Fellow of
both the Australian Institute of Physics and the American Physical Society,
an Honorary Fellow of the Royal Society of New Zealand and an elected
Fellow of the Australian Academy of
Science. He received the Academy’s
Lyle Medal in 2003 for outstanding
contributions to our understanding of
the structure of atomic nuclei and in
2004 he won the Boas Medal of the
Australian Institute of Physics.
In the public arena, George served
as a member of the Australian Prime
Minister’s Select Task Force on Uranium Mining, Processing & Nuclear
Energy during 2006 and continued to
remain active afterward in the public discussion of nuclear technology.
George also continued his research
work until only a few weeks before he
died, including finishing the draft of a
comprehensive and long-awaited review on nuclear isomers that promises
to be essential reading.
George was a gifted scientist who
we knew in various guises and roles.
To his family he was a loving father
and husband, while to his colleagues
he was variously a supervisor, collaborator, fierce competitor, and, for
many of us, a dear friend who will
be greatly missed. George would be
pleased to have the last word, and in
his acceptance speech for a Lifetime
Achievement Award received from
the Hellenic-Australian Chamber of
Commerce and Industry in November 2013, he left us with the following
advice: “My advice to those who follow: Keep up with the new literature,
but go back and read the old papers.
Always be self-critical. Always try and
do things that you feel are a little bit
beyond your reach.”
Greg Lane and Andrew Stuchbery
Australian National University,
Canberra, Australia
Phil Walker
University of Surrey, Guildford,
United Kingdom
Filip Kondev
Argonne National Laboratory,
Chicago, Illinois, USA
calendar
2015
January 19–30
Les Houches, France. Winter
School on the Physics with Trapped
Charged Particles
http://indico.cern.ch/event/315947/
January 26–30
Bormio, Italy. 53rd International
Winter Meeting
http://www.bormiomeeting.com/
February 25–27
Madrid, Spain. The Energy and
Materials Research Conference EMR2015
http://www.emr2015.org/
March 2–6
Valparaiso, Chile. 7th International Conference Quarks and Nuclear Physics - QNP2015
http://indico.cern.ch/event/304663/
May 1–6
Casta-Papiernicka,
Slovakia.
Isospin, STructure, Reactions and
energy Of Symmetry 2015 (ISTROS2015)
http://istros.sav.sk/
May 11–15
Grand Rapids, MI, USA. International Conference on Electromagnetic Isotope Separators and
Related Topics (EMIS-2015)
http://frib.msu.edu/EMIS2015
May 18–23
Oslo, Norway. 5th Workshop on
Nuclear Level Density and Gamma
Strength
http://tid.uio.no/workshop2015/
May 25–29
Urabandai, Fukushima, Japan.
5th International Conference on the
Chemistry and Physics of the Transactinide Elements (TAN 15)
http://asrc.jaea.go.jp/conference/
TAN15/
May 31–June 5
New London, New Hampshire,
USA. Gordon Research Conference
on Nuclear Chemistry
https://www.grc.org/programs.
aspx?id=11762
June 7–12
Hohenroda, Germany. EURORIB2015
http://www.gsi.de/eurorib-2015
June 7–13
Victoria, BC, Canada. 6th International Symposium on Symmetries
in Subatomic Physics SSP 2015
http://ssp2015.triumf.ca/
June 8–12
Budva, Montenegro. Third International Conference on Radiation
and Applications in Various Fields
of Research (RAD 2015)
http://www.rad-conference.org/
June 14–19
Portoroz, Slovenia. Nuclear Structure and Dynamics
http://ol.ijs.si/nsd2015/
June 14–20
Crete, Greece. 2015 International Conference on Applications
of Nuclear Techniques CRETE15
http://www.crete13.org/
June 15–19
Varenna, Italy. 14th International Conference on Nuclear Reaction Mechanisms
http://www.fluka.org/
Varenna2015/
June 21–26
Catania, Italy. 12th International
Conference on Nucleus-Nucleus
Collisions (NN2015)
http://www.lns.infn.it/link/nn2015
June 29–July 3
Pisa, Italy. Chiral Dynamics 2015
http://agenda.infn.it/event/cd2015
July 20–24
Pisa, Italy. 30 years with RIBs
and beyond
http://exotic2015.df.unipi.it/index_
file/slide0003.htm
July 28–30
Liverpool, UK. Reflections on the
atomic nucleus
http://ns.ph.liv.ac.uk/
Reflections2015
August 31–September 4
Groningen, The Netherlands.
European Nuclear Physics Conference (EuNPC 2015)
http://www.eunpc2015.org/
September 6–13
Piaski, Poland. 34th Mazurian Lakes Conference on Physics
“Frontiers in Nuclear Physics”
http://www.mazurian.fuw.edu.pl/
September 14–19
Kraków, Poland. 5th International Conference on “Collective
Motion in Nuclei under Extreme
Conditions” (COMEX5)
http://comex5.ifj.edu.pl/
September 27–October 3
Kobe, Japan. Quark Matter 2015
http://qm2015.riken.jp/
December 1–5
Medellín, Colombia. The XI
Latin American Symposium on Nuclear Physics and Applications
http://www.gfnun.unal.edu.co/
LASNPAXI/
More information available in the Calendar of Events on the NuPECC website: http://www.nupecc.org/
40

Vol. 24 No. 4

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