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Nuclear Physics News
International
Volume 26, Issue 4
October–December 2016
FEATURING:
ISOLDE • Proton-Rich Isotopes • Big Bang Theory
10619127(2016)26(4)
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Nuclear Physics News
Volume 26/No. 4
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Yu-Gang Ma, Shanghai Calin Ur, Bucharest
Richard Milner, MIT
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Vol. 26, No. 4, 2016, Nuclear Physics News 1
Nuclear
Physics Volume 26/No. 4
News
Contents
Editorial
Extreme Light Infrastructure—Nuclear Physics: The Future is Bright at Extremes
by Calin Alexandru Ur................................................................................................................................. 4
Laboratory Portrait
ISOLDE at CERN
by Maria Borge and Yacine Kadi................................................................................................................. 6
Feature Articles
Research on the Origin of the Stable, Proton-Rich Isotopes
by René Reifarth and Michael Wiescher...................................................................................................... 14
Facilities and Methods
How Radioactive Samples and Targets Can Help to Better Understand the Big Bang Theory
by Dorothea Schumann, Massimo Barbagallo, Thierry Stora, Ulrich Köster, and Moshe Gai................... 20
Impact and Applications
Gamma-Ray Inspection of Rotating Object (GIRO)
by Tadashi Kambara..................................................................................................................................... 26
Meeting Reports
The 5th International Workshop on Nuclear Dynamics in Heavy-Ion Reactions (IWND2016)
by Yu-Gang Ma, Feng-Shou Zhang, Lie-Wen Chen, and Chun-Wang Ma................................................... 30
BARYONS 2016: The XIV International Conference on the Structure of Baryons
Volker Crede................................................................................................................................................. 32
Direct Reactions with Exotic Beams 2016, Halifax, Canada
by Rituparna Kanungo, Benjamin P. Kay, and Petr Navratil....................................................................... 35
16th International Conference on Nuclear Structure: NS2016
by Alfredo Galindo-Uribarri........................................................................................................................ 37
News and Views
Paolo Giubellino Appointed New Scientific Managing Director of FAIR and GSI:
Committees Bring Top Italian Researcher to Darmstadt
by Ingo Peter................................................................................................................................................ 39
IUPAP Young Scientist Prize in Nuclear Physics 2016
by Alinka Lépine-Szily.................................................................................................................................. 40
2017 IBA-Europhysics Prize for Applied Nuclear Science and Nuclear Methods in
Medicine Call for Nominations
by Faiçal Azaiez............................................................................................................................................ 41
NEW COVER ILLUSTRATION COPY TO COME.
Cover Illustration: New Copy to come.
2 Nuclear Physics News, Vol. 26, No. 4, 2016
Nuclear
Physics Volume 26/No. 4
News
Contents (continued)
2015 Achievement in Asia Award
by Huan Zhong Huang................................................................................................................................. 41
RAON, the Rare Isotope Accelerator Complex in Korea
by Sunchan Jeong......................................................................................................................................... 42
In Memoriam
In Memoriam: Dirk Schwalm (1940–2016)
by Klaus Blaum............................................................................................................................................. 44
In Memoriam: Paulo Roberto Silveira Gomes (1950–2016)
by Carlos A. Bertulani, Luiz Felipe Canto, Mahir S. Hussein, Jesus Lubian, and
Alinka Lépine–Szily...................................................................................................................................... 45
Book Review
Energy from Nuclear Fission by Enzo De Sanctis, Stefano Monti, and Marco Ripani
by Gianluca Alimonti ................................................................................................................................... 47
Calendar.......................................................................................................................................................... 48
Vol. 26, No. 4, 2016, Nuclear Physics News 3
editorial
Extreme Light Infrastructure—Nuclear Physics:
The Future is Bright at Extremes
Extreme Light Infrastructure (ELI)
aims at establishing an international
laser research infrastructure hosting
the worldwide most advanced ultra-
high power lasers and gamma beam
system. The project was listed in the
2006 road-map of the European Strat-
egy Forum on Research Infrastructure
(ESFRI) and since 2013 it entered the
implementation phase co-financed
with EU Structural Funds. The project
promotes a new concept of pan-Euro-
pean research infrastructure distrib-
uted in several European countries and
operated as a user facility opened to
the whole international scientific com-
munity. The infrastructure will be built
on four pillars, three of them being Figure 1. Exploring new frontiers of Nuclear photonics with advanced laser and
presently in the implementation phase: gamma beams at ELI-NP.
(1) ELI Beamlines in Prague, Czech
Republic, focused on the production of competencies offers a naturally fa- tional collaboration of more than 100
of ultra intense and ultra short pulses vorable environment to answer profi- scientists from 30 countries.
of electrons, protons, and ions; (2) ELI ciently the scientific and technological The major equipment hosted at
Attosecond in Szeged, Hungary, dedi- challenges involved in the implemen- ELI–NP will provide the users laser
cated to the investigation of electron tation and operation of ELI–NP. Two and gamma beams with unprecedented
dynamics in atoms, molecules, plas- well–established international scien- parameters. The ELI–NP infrastruc-
mas, and solids at the attosecond level; tific communities, high-power lasers ture offers unique opportunities in Eu-
and (3) ELI–Nuclear Physics in Bu- and nuclear physics, have joined their rope by providing simultaneously two
charest, Romania, dedicated to laser- efforts at ELI–NP to shape a new in- high-intensity laser beams that can be
based nuclear physics research. terdisciplinary research field. This col- combined within the same experimen-
The ELI–NP facility is being im- laboration proved to be highly prolific tal setup and by the combination of the
plemented by Horia Hulubei National and resulted in a wealth of proposed high-intensity laser with an ultra-bril-
Institute of Physics and Nuclear Engi- research topics covering many areas liant gamma ray system.
neering (IFIN–HH) on the Magurele of interest in fundamental physics, The leading research topics to be
Physics Platform in southern Bucha- nuclear physics and astrophysics as pursued at ELI–NP are focused on the
rest and it is expected to enter opera- well as applications in material and following main directions: (i) laser-
tion in 2019. The Magurele Physics life sciences, material irradiations, in- driven nuclear physics, (ii) character-
Platform concentrates four national dustrial tomography and gamma radi- ization of the laser–target interaction
research institutes of physics and the ography, nuclear waste management by the means of nuclear physics instru-
Faculty of Physics of the University and nuclear security, and pharmaceuti- ments, (iii) photonuclear reactions, (iv)
of Bucharest, making of Magurele a cal radioisotopes. The scientific case of exotic nuclear physics and astrophys-
place where the abundance and density ELI–NP was elaborated by an interna- ics, and (v) development of innovative
The views expressed here do not represent the views and policies of NuPECC except where explicitly identified.
4 Nuclear Physics News, Vol. 26, No. 4, 2016
editorial
applications based on the use of both EuroGammaS Association, a European transferring knowledge and technolo-
high-power lasers and brilliant, narrow Consortium of academic and research gies from the research institutions to
bandwidth gamma beams. institutions (INFN Italy, Sapienza the private sector but it will also facili-
The high-power laser system University Italy, CNRS France) with tate the access of the institutions to the
(HPLS) of ELI–NP consists of two high-tech industrial partners (Scandi- latest technologies and it will provide
10 PW–class lasers based on Optical Nova Sweden, ACP Systems France, support for the ELI–NP research team
Parametric Chirped Pulse Amplifica- COMEB Italy, Alsyom France) having to address and collaborate effectively
tion (OPCPA) driven by a common long-term expertise in the develop- with innovative companies.
dual front-end system and with two ment and building of electron accelera- The connection to the academic
parallel amplification arms. Each am- tors and laser technology. world is made within the Academic
plification arm will provide three out- Besides the important scientific out- Forum of ELI–NP. The Forum gathers
puts with different power levels: 10 come of the facility, the implementa- representative academic and research
PW at repetition rates of 1/60 Hz, 1 tion and operation of ELI–NP will also institutions in a joint effort to exploit
PW at repetition rates of 1 Hz, and 100 have a significant economical impact the unique opportunities opened by
TW at repetition rates of 10 Hz. Out of at the national and international levels. ELI–NP and to eventually establish a
the six possible outputs, two of them, The companies involved in the imple- reference center for scientific culture in
one from each arm, can be provided si- mentation of the project will acquire Magurele. Education and research will
multaneously for experiments. For the the expertise to realize beyond state- benefit from the excellent conditions
two 10 PW outputs an unprecedented of-the-art technologies and equip- and unique experimental capabilities
level of intensity of about 1023–1024 ment. During the operational phase offered by ELI–NP. The new exciting
W/cm2 will be achieved, opening new companies will develop and provide research opportunities opened by ELI–
research opportunities in laser-driven technologically advanced scientific NP will attract the best students and re-
particle acceleration and nonlinear equipment, spare parts, services, and searchers from all over the world. The
QED. The HPLS at ELI–NP is being maintenance. relation with the academic institutions
built and installed by Thales Optron- As a large-scale research infrastruc- will guarantee the long–term needs of
ique France and Thales Romania. ture ELI–NP will act as a catalyst for the new facility in terms of Ph.D. stu-
The Gamma Beam System (GBS) connecting the research community dents and junior researchers.
of ELI–NP was designed to provide a with both the academic and industrial By 2018 ELI–NP will count 250
very intense and brilliant gamma beam sectors. The ELI–NP facility presents employees at all levels of qualifica-
with continuously tunable energy multiple interests in terms of versatil- tion: senior and junior researchers,
based on incoherent inverse Compton ity of equipment and, as such, should Ph.D. students, engineers, and techni-
scattering of a high repetition pulsed be able to attract various industries cians. To reach this milestone person-
laser light off a high intensity, low looking for a facility offering access nel recruitment is given high prior-
emittance, relativistic electron beam. to state-of-the-art equipment, support ity. Details on the job opportunities
Advanced electron linear accelerating services by excellent researchers, and at ELI–NP can be accessed at http://
techniques and high quality laser de- training services with the latest tech- www.eli-np.ro/job.php.
vices are combined into a high lumi- nologies.
nosity electron–photon collider. The An adequate environment for
key parameters of the gamma beams breeding the partnership with the in-
to be provided at ELI–NP are orders dustrial and academic worlds was
of magnitude better than the present- created within the framework of two
day state-of-the-art: relative bandwidth collaboration forums. The Magurele
(BW) better than 0.5%, spectral den- High-Tech Cluster is an open associa-
sities of about 10,000 photons/s/eV, tion of research and business entities
photons energy continuously variable focused on developing relations with
in the range 0.2–19.5 MeV, peak bril- the economic environment and high-
liance higher than 1021 photons/mm2/ tech industries. It already gathered
mrad2/s/(0.1%BW), and high degree of over 50 small and medium enterprises
linear polarization (higher than 95%). involved in developing technologi-
The building and installation of the cally advanced products. The cluster Calin Alexandru Ur
ELI–NP GBS will be performed by will provide not only the means for ELI–NP/IFIN–HH
Vol. 26, No. 4, 2016, Nuclear Physics News 5
laboratory portrait
ISOLDE at CERN
Introduction stability, combined with technological collaboration has designed a versatile
ISOLDE’s story begins in 1967, advances in the field, have triggered facility that constitutes an attractive
when the first on-line production of the move of radioactive beam experi- option for a wide variety of nuclear
radioactive nuclei for experiments ments from a very specific research structure, nuclear astrophysics and
took place in a newly provisional way. subject to the mainstream. Theoretical other radioactive beam experimental
Almost half a century later, ISOLDE developments challenge experimental studies. This laboratory portrait ad-
is the oldest experiment still in opera- advances, a challenge that ISOLDE, dresses the development of ISOLDE
tion at CERN, and for good reasons: to stay at the forefront, is ready to since the previous laboratory portrait
it occupies a leading position in the face with the High Intensity and En- [7]. It presents a short overview of the
field of nuclear research, having pro- ergy upgrade (i.e., HIE-ISOLDE). facility, described in detail in Ref. [7],
duced nearly 1300 nuclei of more than The upgrade project was approved with a focus on the technical develop-
70 elements [1]. Over the years, it has by CERN in September 2009 and is ments and scientific opportunities of
developed into a facility dedicated to in accordance with NuPECC’s 2010 the HIE-ISOLDE upgrade.
fundamental science and its applica- Long Range Plan for Nuclear Science Like other CERN experiments,
tions. ISOLDE’s success can be traced in Europe [6], which calls for major ISOLDE is governed by an inter-
to two key elements. One is the con- upgrades of large-scale nuclear phys- national collaboration, which was
tinuous development of new radioac- ics facilities. HIE-ISOLDE, now well formed in April 1965 and presently
tive ion beams and steady improve- under way, opens up new horizons for includes 18 members from three con-
ment of experimental conditions. The exotic nuclei research by increasing tinents. The collaboration safeguards
other is the vibrant ISOLDE collabo- the current energy and intensity reach, the ISOLDE facility, helping CERN
ration and researcher community, with upgrading existing equipment, and maintain the technical infrastructure
their ability to adapt to the changing developing novel experimental instru- and operate it in the most efficient way.
physics landscape, developing new mentation. In a nutshell, the ISOLDE It follows and is in continuous contact
ideas and devices that allow the con-
tinuous production of science at the
forefront. Figure 1 shows a 3D layout
of the facility.
Most experiments hosted at
ISOLDE focus on nuclear physics,
while some follow other lines of re-
search, such as atomic physics, astro-
physics, and fundamental interactions.
There is also a vibrant program in the
field of applications, ranging from
solid-state physics to life sciences.
Recent highlights of research con-
ducted at ISOLDE include the deter-
mination of the ionization potential of
At [2], studies of pear-shaped nuclei
by Coulomb excitation [3], as well as
the investigation of the emerging new Figure 1. 3D layout of the ISOLDE facility. One can see the different parts of
magic numbers far from stability, in the facility: the two target stations and corresponding mass separators (i.e., HRS
particular N = 32 and N = 34 by the and GPS), the low energy experiments (i.e., COLLAPS, CRIS, IDS, ISOLTRAP,
determination of the masses of 51–54Ca NICOLE, TAS, VITO, and WITCH). In the high energy part REX and the HIE
[4] and the radius of 40–52Ca [5]. linac with six cryomodules in place and the three beam-lines are shown. In the
The observation of significant back, one can see MEDICIS, dedicated to investigating the production of novel
changes in nuclear structure far from isotopes for medicine.
6 Nuclear Physics News, Vol. 26, No. 4, 2016
laboratory portrait
with the external international ex-
pert committee, INTC (ISOLDE and
Neutron Time-of-Flight Experiments
Committee), which meets regularly
and determines the scientific program.
ISOLDE has also forged technical col-
laborations with other nuclear physics
laboratories around the world, such as
GANIL-SPIRAL1-2 in France, RISP
in South Korea, SPES in Italy, and
TRIUMF in Canada.
The ISOLDE Facility
ISOLDE produces radioactive ion
beams in spallation, fragmentation,
and fission reactions between stable
Figure 2. Chart of nuclei produced at ISOLDE given in ions per μC of proton
nuclei from thick targets and high-en-
beam on target. Twenty-five materials combined with three types of ion sources
ergy and high-intensity proton beams
allow for the production of such a large diversity of beams.
accelerated in the first ring of the
CERN accelerator complex, the Pro-
ton Synchrotron Booster (PSB). The the fastest targets that reach more than ment, the wavelength of various laser
proton beam hits the hot target typi- 2000°C. Target materials partly deter- beams is precisely tuned so that the
cally with an energy of 1.4 GeV and mine the radioactive nuclei production energy of photons matches the transi-
an intensity of up to 2 μA. Reaction rate and their release time, thus a care- tion energies of the atom of interest.
products diffuse out of the target into ful selection is of paramount impor- As a result, only that specific element
an adjacent ion source and, following tance. ISOLDE offers more than 25 is ionized, while the rest remain unaf-
ionization, they are extracted and sep- target materials, with uranium carbide fected. Laser ionization takes place in
arated to produce the ion beam of the being the most requested because of the line kept at low temperature, ap-
desired element. The ISOLDE beam is its versatility. proximately 1700°C. Atoms remain
then delivered to the different experi- The atomic fragments that have in the cavity for an average of 100 μs,
mental stations or post-accelerated. been released from the collision enter thus a high repetition rate (10 kHz)
an ion source that ionizes the elements laser system is necessary to minimize
Target and Ion Source of interest, thus significantly influenc- duty cycle losses. Plasma ion source
The heart of ISOLDE is its target ing the production rate of radioactive coupling to RILIS has also been tested.
and ion source system, which provide nuclei and the purity of the subsequent RILIS is presently equipped with two
the selective production of the desired beam. Nd:YAG lasers, three dye lasers, three
isotopes. The production process be- ISOLDE uses three types of ion solid-state titanium-sapphire (Ti:Sa)
gins when the target, heated between sources: surface, plasma, and laser. Al- lasers and a blaze laser to be able to
700°C and 2000°C depending on the though surface and plasma ionization work in transition saturation mode.
material, is bombarded by the pro- are both efficient, a higher degree of Since its installation, it has become an
ton beam and the already mentioned chemical selectivity can be achieved attractive option for ISOLDE experi-
nuclear reactions occur either by boil- with the Resonance Ionisation La- ments and is used for about three quar-
ing off a few protons or neutrons or ser Ion Source (RILIS), a method ters of the facility’s annual schedule.
fragmenting them in lighter species. pioneered by ISOLDE. RILIS takes For more details, see Ref. [8] where a
The high temperature allows the fast advantage of resonant excitation of list of available beams and their ion-
release of radioactive nuclei before atomic transitions using tunable laser ization schemes is given.
their decay. Release times vary from radiation and allows a high degree of Following ionization, the next
a few dozens of seconds for targets isobar-free selectivity. Each element “stop” in the ion beam’s route through
with temperatures between 700°C and has a unique electron energy-level the facility is one of ISOLDE’s two
1400°C to a few tenths of a second for structure. To selectively ionize an ele- mass separators, the High Resolu-
Vol. 26, No. 4, 2016, Nuclear Physics News 7
laboratory portrait
tion Separator (HRS) or the General the separators has a time structure for low intensities, favoring the study
Purpose Separator (GPS). The HRS dictated by the half-life of and the ef- of rare species.
uses two bending electromagnets and fusion and diffusion times for a spe- Beams are then charge-bred to
an elaborate ion optical system to cific isotope in the primary target. It multiple charge states in REXEBIS,
achieve a mass resolving power, M/ typically consists of a singly charged an electron beam ion source, with a
ΔM, up to 5,000 units in the present ion beam ranging in energy from 30 to mass-to-charge ratio commonly be-
configuration. The GPS can reach a 60 keV. To minimize beam transmis- tween 2.5 and 4.5. Ions are trapped
mass resolving power of about 1,000, sion losses, REX takes advantage of in a confined space and ionized via
as it is equipped with one bending an innovative scheme that consists of impact with an intense electron beam.
magnet and electrostatic switchyard, a cylindrical gas-filled Penning trap, As the intensity of radioactive ions is
and offers the possibility of extracting REXTRAP, and an electron beam ion limited in comparison to that of re-
three mass-separated beams simul- source, REXEBIS. The beam of sin- sidual gas ions—mainly C, N, O, Ne,
taneously with a mass difference of gly charged ions first undergoes lon- and Ar—a mass separator consisting
4–15% of the central mass. The com- gitudinal cooling at REXTRAP. The of a 90° electrostatic deflector and a
bined use of RILIS and the mass-sep- beam is electrostatically decelerated 90° magnetic bender in a vertical S-
arating magnets allows experiments by passing the potential barrier of the shape separates ions based on their en-
to select the isotope of interest of the trap. At a certain gas pressure, the ions ergy. The breeding time in REXEBIS
desired chemical element, leading to that lose energy in the collision are not depends on the desired A/q and mass,
the production of a high-purity radio- able to leave the trap. Following ac- ranging from 20 ms for light nuclei up
active ion beam. A list of the available cumulation and further radial cooling, to a few hundreds of milliseconds for
isotopes at ISOLDE and their produc- the ions are released in a short pulse the heavier species.
tion per μC of proton beam on target is and undergo transversal cooling via Following charge multiplication,
shown in Figure 2. the sideband cooling method, devel- ion bunches are injected into the 11 m
oped at ISOLDE. Ne or Ar is the buf- compact linac that consists of a ra-
fer gas most commonly used. REX- diofrequency quadrupole (RFQ) ac-
REX-ISOLDE
TRAP has an efficiency of 50–60% celerator, a 20-gap interdigital H-type
Nuclei at the edge of stability can
and offers the significant advantage of (IH) structure, and three 7-gap resona-
reveal interesting aspects of nuclear
especially fast beam cooling; in fact, tors with a frequency of 101.28 MHz.
interaction and dynamics. To gain a
the heavier the ions the faster they are REX accelerates ions from 5 keV/u to
complete picture of the atomic nucleus
cooled. Further, the efficiency is better 0.3 MeV at the RFQ, then to 1.1–1.2
and address the collective and individ-
ual properties of nuclei, it is important
to perform reaction studies, which are
only possible with accelerated radio-
active ion beams. This is a challenge
that has been addressed in the past
by the radioactive beam experiment
(REX) post-accelerator [9, 10]. REX
can accelerate radioactive ion beams
at energies from 0.3 to 3 MeV/u and
mass over charge ratio, A/q, from 2.5
to 4.5. REX began operation in 2001
as an experiment based on the exper-
tise of groups working at ISOLDE and
built by a few universities from Ger- Figure 3. The ISOLDE post-accelerator, as used in 2016. REXEBIS can be seen
many and Sweden. Thanks to its suc- on the platform and REXTRAP is located underneath to save space. After the
cess, it has developed into a facility Nier type spectrometer, the normal conducting linac consists of a radiofrequency
and it is presently fully incorporated quadrupole accelerator, a 20-gap interdigital H-type (IH) structure and three
in the ISOLDE infrastructure. 7-gap and one 9-gap IH structures, allowing energies of up to 3 MeV/u. Two
The low energy quasi-continuous superconducting cryomodules are installed downstream of the linac and enable
beam that is delivered to REX after it to reach 5 MeV/u.
8 Nuclear Physics News, Vol. 26, No. 4, 2016laboratory portrait
MeV/u at the IH structure and finally
to 1.55, 1.88, and 2.2 MeV/u at the
7-gap resonators. The success was
such that the community started ex-
ploring options for an energy upgrade
almost immediately. In 2004, a 9-gap
IH structure operating at 202.56 MHz
was added to extend the energy range
to 3 MeV/u (Figure 3). REX proved
to be a very versatile machine, ca-
pable of accelerating a wide range of
ion beams, from light mass nuclei (A
< 40), namely 6He and 8Li, to heavy
elements (e.g., 224Ra) [10].
REX opened up new opportuni-
ties for research in nuclear structure
far from stability. Its post-accelerated
beams were ideal for Coulomb excita-
tion experiments. Capture and transfer
reaction studies, as well as elastic and
inelastic scattering experiments were
limited to light masses due to the lim- Figure 4. Layout of a high-β cryomodule. The cryomodule containes five su-
ited acceleration energy. A review of perconducting RF cavities and a superconducting solenoid magnet between the
the main results obtained in a decade second and the third cavity. The helium vessel can be seen above them. The
of physics with REX can be found in countries of the manufacturers of the different parts are shown.
Ref. [10].
HIE-ISOLDE Energy Upgrade Figure 3 for the coupling to REX. A
The success of the REX post-ac- The construction of a new super- geometrical beta, βg, of 10.3% of the
celerator paved the way toward higher conducting linear accelerator (HIE- speed of light corresponds to the de-
energies, as they allow for multistep linac) [9] aims to increase the en- signed speed value of the beam, for
Coulomb excitation and therefore de- ergy range of REX from 3 MeV/u to which the accelerating efficiency of
fine the shape without large theoretical 10 MeV/u. Its accelerating structure is the cavity is maximum. In stage two,
constraints. Furthermore, the increase similar to that of the LHC, benefitting expected to be completed in 2018,
of energy will allow for the study of from cryogenics, superconducting ra- HIE-linac will be equipped with two
one or two nucleon transfer reactions diofrequency, and beam instrumenta- additional cryomodules with the same
at middle mass nuclei. In this way, tion techniques that were developed configuration to reach 10 MeV/u for
both collective and single particle for the LHC ring. A/q = 4. The third cryomodule is cur-
properties are addressed. A large pal- HIE-linac will be equipped with 32 rently in the cryo-lab, awaiting instal-
ette of reaction studies, from elastic radiofrequency (RF) cavities housed lation in 2017. The fourth one will be
to quasi-fission, will be available. The in six cryomodules and replace the assembled in 2017 and installed in
way forward to enhance the ISOLDE 9-gap and 7-gap resonators of REX, 2018, completing the energy upgrade.
research capabilities naturally led to in an upgrade that takes place in The third and final stage involves the
the next major upgrade of the facil- three stages. In the first stage, which manufacturing and installation of two
ity: HIE-ISOLDE. The HIE-ISOLDE is already finished, two cryomodules, more cryomodules, each housing six
project has three main goals: to in- each containing five superconducting low-β (βg = 6.3%) cavities and two
crease the energy of the radioactive high-β (βg = 10.3%) cavities operating superconducting solenoids. They will
ion beam from 3 MeV/u to 10 MeV/u, at 101.28 MHz and a solenoid mag- replace the main parts of the normal
to increase beam intensity and purity, net, were designed, coupled to REX- conducting linac and allow for de-
and to improve secondary beam char- linac and commissioned, increasing celeration of the beam, providing ac-
acteristics [11]. the beam energy to 5.5 MeV/u, see cess to a wider range of low energies.
Vol. 26, No. 4, 2016, Nuclear Physics News 9laboratory portrait
Plans for the third stage of the energy
upgrade foresee the insertion of a pre-
buncher to the RFQ accelerator at a
subharmonic frequency, which would
allow increased bunch spacing with-
out a major transmission loss. There
are also plans to add a beam chopper
between the RFQ and the 20-gap IHS
to clean the background of satellite
bunches. In general, REX and HIE-
linac deliver pulsed beams of a rep-
etition rate up to 50 Hz. The total ef-
ficiency of the post-accelerator varies
between 1 and 10% depending on the Figure 5. Layout of the HIE-linac after the installation of the third high-β cryo-
requested beam. module in 2017. At the end of the first beam-line, XT01, MINIBALL is located, at
The high-β RF cavities of HIE- the second (XT02) the ISOL Solenoidal Spectrometer, ISS, and the third, XT03, is
linac are made of copper, sputter- reserved for movable setups. In the drawing, XT03 is occupied by the scattering
coated with niobium, a technique chamber, SEC, which is presently connected to XT02.
invented at CERN and first adopted
for the electron accelerating cavities
of LEP. Later, the design was revis- between two cryomodules is only 370 efficiency close to 100%. Presently
ited at Legnaro, Italy, and adapted to mm, 90 mm of which are reserved for two beam-lines have already been in-
accelerate heavy ions. Bulk copper diagnostic boxes. New beam diag- stalled and are operative; a third one
was used in the manufacture of the nostic elements have been developed will become operative in 2017 along
HIE-ISOLDE cavities to minimize for HIE-linac to measure intensity, with the third cryomodule (Figure 5).
the number of electron beam weld- energy, and transverse profiles. These
ing. Sensitivity to helium pressure include Faraday cups, collimators Intensity Upgrade
fluctuations was reduced by adapting of different diameters, and V-shaped Higher beam intensities are vital for
the shape of the helium reservoir. The slits that measure the beam transverse realizing measurements in a shorter
RF cavities are equipped with a power profile. The diagnostic boxes are also time and, more importantly, for the
coupler and a tuning system, both de- equipped with Si detectors that deter- production of more exotic isotopes,
signed at CERN. mine beam energy and longitudinal thus a high-intensity upgrade (see Ref.
The superconducting solenoid profiles; it is worth noting that the [12] for an overview) is necessary.
magnet is integrated in the common time-of-flight between different Si de- The most straightforward way to
vacuum system of the cryomodule and tectors will be used to obtain the most produce radioactive ion beams with
provides transverse beam focusing at precise measurements of radioactive higher intensities is to increase pri-
the HIE-linac (Figure 4 for the layout beams. Several diagnostic boxes in mary beam intensity. ISOLDE will
of the cryomodule). The existence between cryomodules and along the benefit from a wider upgrade to the
of adjacent superconducting cavities experimental beam-lines allow the de- CERN injector chain, when Linac4
means that strict specifications are im- termination of the properties of the ac- will begin operation in 2021 after the
posed on the remnant magnetization celerated beam when it arrives to the CERN second long shut down, LS2,
to avoid flux trapping and on the stray experiment. which is foreseen for the years 2019
field at nominal current. Three identically designed beam- and 2020. This upgrade will raise the
Following acceleration at HIE- lines connect the linac with the ex- intensity of the proton beam by a fac-
linac, the beam enters a high-energy perimental devices. In each of them, tor of three from the present 2 μA to
beam transfer line (HEBT), specially the beam is bent by 90 degrees by two 6.7 μA. The PSB will also undergo
designed to preserve beam emittances. dipole magnets and at least a doublet- an upgrade to increase the extraction
It is thus necessary to reduce the drift quadrupole to focus the beam into the energy from 1.4 GeV to 2 GeV, leav-
space between the cavities. The accel- experimental station. The HEBT is de- ing the possibility to use both energies
erator is very compact and the distance signed to reach an absolute transport for physics depending on the dominat-
10 Nuclear Physics News, Vol. 26, No. 4, 2016laboratory portrait
ing reaction process. The increase in infrared and blue spectrum, thus of- A new design for the REXEBIS
energy will affect the various reaction fering more choice of ionization paths charge breeder is currently under de-
processes differently. Simulations us- and the ability to saturate the ionization velopment in collaboration with the
ing the ABRABLA or FLUKA codes path. This new addition has doubled Brookhaven National Laboratory
have been done for the expected the production of many nuclei. Ioniza- (BNL). To increase the intensity and
yields. The fission cross-section will tion schemes for Li, Ge, Te, Ba, and improve the repetition rate of the ion
decrease and the production will be Ho were identified for the first time at beam, it is necessary to address the
barely compensated by secondary pro- ISOLDE in the past three years. The ultra-high vacuum, the electron cur-
cesses, while fragmentation and spall- present number of chemical elements rent and density, the high voltage, and
ation cross-sections will increase by a that can be resonance ionized with la- the magnetic field. Preliminary tests of
factor from two to ten. ISOLDE plans ser at ISOLDE exceed thirty-five. For a prototype electron gun with a pulsed
to retain the proton beam energy of 1.4 recent achievements, see Ref. [8]. electron beam of 1.5 A and 30 keV are
GeV for fission product studies. Selectivity can be significantly im- ongoing at BNL and have already pro-
The energy and intensity increase proved by optimizing hot cavity mate- duced promising results.
of the primary proton beam results in rials. Studies were conducted to deter-
higher radiation levels, thus limiting mine the performance and suitability
the lifetime of the target. Temperature of high temperature, low work func- Physics Opportunities
variations in the target material pres- tion materials, such as glassy carbon The HIE-ISOLDE upgrade sub-
ent another challenge, as they are of- or tungsten impregnated with a mix- stantially enhances research opportu-
ten responsible for production losses. ture of barium oxide and strontium nities in nuclear structure studies and
Taking these factors into account, a vi- oxide (BaOSrO on W) or with gado- nuclear astrophysics. The wide variety
tal component of the intensity upgrade linium hexaboride (GdB6). The instal- of exotic nuclei produced at ISOLDE,
addresses the target and ion source lation of a laser ion source trap (LIST) their availability at different energies,
connections to the rest of the ISOLDE also boosted selectivity. LIST uses a and the new instrumentation that has
facility. Options for new target materi- positively charged repeller electrode been developed pave the way for a
als are explored, with a focus on radia- to prevent unwanted atoms in the hot robust physics program in the com-
tion resistance. Target materials that cavity where the atoms of interest are ing years. The project has received
are presently used were extensively laser-ionized. The first off-line tests significant interest and over thirty-five
tested to examine their suitability to showed that LIST reduced surface experiments have already been ap-
higher radioactivity levels. Studies ionized isobaric contamination by up proved.
were also made to optimize the heat- to four orders of magnitude. In 2012 The approved HIE-ISOLDE exper-
ing process to uniformly distribute the first on-line experiments using iments address fundamental questions
heat across the target system and min- LIST were performed and enabled the of nuclear physics: dipole excitation,
imize the power needed for heating. first in-source laser spectroscopy of isospin conservation, interplay of sin-
Research into target geometry modifi- 217Po and 219Po. gle and collective degrees of freedom,
cations and improvements to the target The upgrade of HRS aims to re- shape coexistence, as well as octu-
change systems is also undertaken. duce isobaric contamination that can pole degrees of freedom. In the light
The ion source upgrades focus disturb experimental measurements. nuclei, the dipole strength in 11Li and
mainly on RILIS—involving the up- In the HRS, the two existing magnets elastic scattering of 8B will be investi-
grade of the laser setup, the develop- will be replaced with a pre-separator gated. In the middle mass region, the
ment of new ionization schemes, and to retain unwanted isotopes in the validity of the shell model description
the improvement of selectivity—and shielded target area, an RFQ Cooler around 78Ni will be explored. Shape
on the efficient coupling with other and Buncher (RFQCB) and a single coexistence studies are proposed in
ion sources, such as the FEBIAD ion high-resolution separator magnet. The the region of neutron deficient Se and
source, VADLIS. The main upgrade RFQCB is designed to improve com- Kr isotopes, as well as in the neutron
of the laser setup has already been patibility with other beam-line compo- deficient region around Z = 82. In
achieved. RILIS’s copper vapor lasers nents by improving gas pressure sta- the heavy mass region, Coulomb ex-
were replaced over the last decade bility and vacuum pressure variation. citation experiments will investigate
with industrial solid-state lasers that A prototype has already been built and quadrupole and octupole collectivity
extended the wavelength range into the installed in the off-line separator. in Te, Xe, and Ba isotopes, to unravel
Vol. 26, No. 4, 2016, Nuclear Physics News 11laboratory portrait
eter will complement the Coulomb
excitation studies of the heavy nuclei
and those involving high multipolarity
transitions. The T-REX silicon particle
detector setup is optimized for transfer
reaction studies. T-REX identifies the
light reaction products and measures
their angular distribution for a large
range of polar angles. In combination
with MINIBALL, it reconstructs the
excitation energy in the final nucleus
with high resolution. T-REX is an ex-
cellent instrument for the study of sin-
gle particle properties of exotic nuclei
far from stability [15].
In addition, there is a general pur-
pose ScattEring Chamber (SEC), used
for reaction studies, in which gamma-
ray information is not necessary. It can
Figure 6. Doppler corrected gamma ray spectrum of 4.5 MeV/u 142Xe beam host different charged particle detector
Coulomb excited on 206Pb target (in red) and the equivalent gamma spectrum arrays for elastic, inelastic, and trans-
for 2.8 MeV/u 142Xe beam on a 96Mo target (in blue). The higher energy 142Xe fer studies, including the corset setup
allows for the population of at least the 8+ state in the multistep Coulomb excita- from GSI to perform quasi-fission re-
tion process. The previously assigned 3– to 2+ transition [17] indicating octu- action measurements. The ISOL Sole-
pole correlations is not observed at the expected energy. Courtesy of C. Henrich. noidal Spectrometer (ISS), for highly
efficient (d,p) reaction studies will
be ready for physics experiments in
the structure around the doubly magic (p,α) reaction in 59Cu at the relevant 2018. Some approved experiments in-
nucleus 132Sn. astrophysical energies. corporate other instrumentation, such
Transfer reaction experiments were From the point of view of instru- as the active target ACTAR, the opti-
previously confined to light nuclei due mentation, new devices are contem- cal time projection chamber, and the
to the energy limit, 3 MeV/u, of REX. plated beyond the work horse (i.e., tilted foil beta-NMR setup. A proposal
The high-energy upgrade is beneficial the high-resolution MINIBALL array has been made for the installation of a
for transfer reaction studies of rela- [13]). MINIBALL—in operation for zero-degree spectrometer after MINI-
tively heavy nuclei. Some transfer more than a decade—performs gamma BALL, which could identify reaction
reaction experiments are motivated ray detection, a key ingredient of products and physically separate iso-
by unsolved questions in nuclear as- Coulomb excitation experiments and baric beams or other contaminants.
trophysics and specifically stellar needed in many transfer reaction ex- The TRIμP spectrometer [16], cur-
nucleosynthesis. The long-standing periments. It consists of 24 segmented rently located in KVI-CAR, is a good
7Li abundance anomaly is addressed high-purity Ge detectors contained in candidate and could be transferred to
by revisiting the resonances in 8Be groups of three in eight cryostats and CERN and installed in the ISOLDE
around 20 MeV excitation energy. The arranged around a target. The array is hall in 2019–2020.
levels just above the neutron threshold equipped with a double-sided silicon
in 18N will be studied via (d,p) reac- strip detector array of CD type that al- Outlook
tion, as the N neutron capture reac- lows the determination of the ejectile In October 2015, the first physics
tion rate could play an important role and its scattering angle. MINIBALL experiment marked the beginning of
in the r-process for elements heavier will be complemented by the SPEDE operations for HIE-ISOLDE, which
than iron. The intense Cu beams at spectrometer that performs in-beam was then equipped with one cryomod-
ISOLDE and the available post-accel- conversion electron-gamma-ray spec- ule. It performed Coulomb excitation
erated energies are ideal to study the troscopy [14]. The SPEDE spectrom- of neutron-rich Zn isotopes. While
12 Nuclear Physics News, Vol. 26, No. 4, 2016laboratory portrait
writing these lines, two new experi- lent and thus ISOLDE is looking at a 12. R. Catherall et al., Nucl. Instrum. Meth-
ments have been conducted with two bright, active future. ods Phys. Res., Sect. B 317 (2013) 204.
cryomodules already operative. The 13. N. Warr et al., Eur. Phys. J. A 49 (2013)
first addresses the study of electro- 40.
Acknowledgement 14. P. Papadakis et al., JPS Conf. Proc. 6,
magnetic properties of the excited A successful project such as HIE- (2015) 030023.
states of 110Sn that shows anomalous ISOLDE has many contributors; we 15. V. Bildstein et al., Eur. Phys. J. A 48
behavior. The second aims to de- would like to thank them all for their (2012) 85.
termine the octupole correlations in efforts during the last decade, pres- 16. P. Deendoven, AIP Conf. Proc. 831
142Xe as indicated by the previous ob-
ently and in the future until all aspects (2006) 39.
servation of a 3– to 2+ transition. The of this ambitious project are imple- 17. W. Urban et al., Eur. Phys. J. A. 16
purity of the ISOLDE beams and the mented. Special thanks to A. Papa- (2003) 303.
use of Coulomb excitation to populate georgiu Koufidou for her contribution
the state from the bottom help to better to this article.
elucidate the structure. Figure 6 shows
the on-line spectrum of Coulomb ex- References
cited 142Xe using a Pb target. Five 1. M. J. G. Borge, Nucl. Instrum. Meth-
more experiments are planned for ods Phys. Res., Sect. B 376 (2016)
2016, from transfer reactions in 9Li to 408.
Coulomb excitation in 132Sn passing 2. S. Rothe et al., Nature Commun. 4
by the gamma strength of 66Ni. The (2013) 1835.
requested post-accelerated energies 3. L. P. Gaffney et al., Nature 497,
for these experiments expand from 4 (2013) 199.
MeV/u for heavy beams to 6.5 MeV/u 4. F. Wienholtz et al., Nature 498, (2013)
346. Maria Borge
in the case of the 9Li beam. The suc-
5. R.F. Garcia Ruiz et al., Nat. Phys. 12, ISOLDE Leader and
cess of the different experiments has
(2016) 594. Collaboration spokeperson
demonstrated the capacities of HIE- 6. NuPECC Long Range Plan 2010: per- CERN,
ISOLDE and the physics opportunities spectives of Nuclear Physics in Eu- On leave from IEM-CSIC, Madrid, Spain
that lie ahead thanks to the upgrade. rope. http://nupecc.org.
Almost fifty years since the be- 7. A. Herlert, Nucl. Phys. News 20
ginning of its operation, ISOLDE (2010) 5.
remains a leading facility in terms of 8. S. Rothe et al., Nucl. Instrum. Meth-
both technical infrastructure and pro- ods Phys. Res., B 376 (2016) 91.
duction of frontier physics. The key to 9. M.J.G. Borge, K. Riisager, Eur. Phys.
the facility’s success is its continuous J. A52 (2016) 334.
transformation to stay at the forefront 10. P Van Duppen and K. Riisager, J.
Phys. G: Nucl. Part. Phys. 38 (2011)
of nuclear physics research. The HIE-
024005.
ISOLDE upgrade showcases CERN’s 11. M. Lindroos and T. Nilsson, eds.,
support of scientific diversity, which HIE-ISOLDE: the technical op-
is the foundation of the Organization’s tions, CERN Yellow Report (2006)
strength. The physics opportunities CERN-2006-013, http://cds.cern.ch/ Yacine Kadi
with the low energy and post-acceler- record/1001782/files/CERN-2006- HIE-ISOLDE Project Leader,
ated beams at HIE-ISOLDE are excel- 013.pdf. CERN
Vol. 26, No. 4, 2016, Nuclear Physics News 13feature article
Research on the Origin of the Stable,
Proton-Rich Isotopes
René Reifarth1 and Michael Wiescher2
1Goethe University Frankfurt, Frankfurt, Germany
2University of Notre Dame, Notre Dame, Indiana, USA
The Nucleosynthesis of the Heavy Elements
The beginning of our universe as we know and inter-
pret it was the Big Bang. About 14 billion years ago, the
entire universe started to expand. This expansion was ac-
companied by a global cool down of all matter and radia-
tion forming the universe. A few minutes after the Big Bang
the constituents of the atomic nuclei, protons and neutrons,
were formed. Further cooling allowed the formation of the
first complex nuclei made from protons and neutrons, in
particular the new element helium-4 consisting of 2 protons
and 2 neutrons. The matter consists now basically of 75%
hydrogen (protons) and 25% helium.
It took about 400 million years until heavier elements
were formed in significant (less than 1%) amounts. The fu-
sion of hydrogen into helium is the energy source of almost Figure 1. The solar abundances of the atomic nuclei as a
all stars that can be observed today—including our Sun. function of their mass. The structures observed can be ex-
Once the hydrogen in the core is depleted, the temperature plained by different processes contributing to the overall
and density rises and three helium nuclei fuse into carbon. nucleosynthesis. The lightest elements—hydrogen, heli-
Later stages of stellar burning lead to the charged-particle- um—are produced in the Big Bang (red) while the elements
fusion-based production of all the elements up to iron. up to iron are synthesized during stellar burning phases via
The elements heavier than iron are byproducts of the fusion of charged particles (beige). During the extremely
energy-producing fusion stages of the stellar evolution [1]. hot last stellar burning phase—the silicon burning—the
Typically they cannot be formed through fusion of charged isotopes around iron (mass 56), which are most tightly
particles, because the Coulomb repulsion of the necessary bound, are produced in the nuclear statistical equilibrium
heavy partners cannot be overcome at stellar temperature (grey). Almost all of the elements with higher proton num-
and density conditions. The overwhelming majority of bers than iron are produced through neutron-induced pro-
those elements are formed through sequences of neutron cesses (blue) [3].
captures and beta-decays starting from an abundant seed—
typically iron [2]. These processes are summarized in Fig-
ure 1. While roughly 50% of these isotopes are formed by process was based on the assumption of a sequence of pro-
slow neutron capture (s-process) during the helium and ton-capture reactions similar to the rapid neutron capture
carbon burning phases of stellar evolutions, the remaining process on the neutron-rich side of the valley of stability.
50% are formed by rapid neutron capture (r-process) during This generic production process was accordingly called the
explosive events such as supernovae explosions or merging p process [4].
neutron stars.
However, there are about 40 stable isotopes abundant in The p Process
the solar system, which cannot be explained by any of the The p nuclei are 37 neutron-deficient, stable isotopes
mechanisms described so far. These isotopes are heavier heavier than iron. Their origin cannot be explained by
than iron, lighter than bismuth, and on the proton-rich side neutron-induced reactions. The p nuclei are typically 2–3
of the valley of stability. These isotopes are traditionally orders of magnitude less abundant than the other stable
named p nuclei because the initially proposed production isotopes of the same element. This suggests a production
14 Nuclear Physics News, Vol. 26, No. 4, 2016feature article
Atomic nuclei and their constituents: Each atom consists of Z electrons carrying –Z times the elemen-
tal charge and a nucleus with the +Z. The nucleus consists of Z protons carrying the charge and N neu-
tral neutrons. Since nucleons, protons and neutrons, have almost the same mass and are much heavier
than the surrounding electrons, the sum A = Z + N of the number of nucleons is often called the (atomic)
mass number. In contrast to neutrons, free protons are stable and form the lightest chemical and most
abundant element, hydrogen. Only about 300 combinations of Z versus N form stable nuclei and can be
found in the solar system. Very roughly nuclei with N = Z form stable nuclei. The corresponding area in
the N-Z-plane is called the valley of stability. The second most abundant nucleus in the universe consists
of 2 protons and 2 neutrons, the α-nucleus or helium-4. If nuclei outside this valley are produced in stars
or on earth, they usually decay back toward stability conserving the mass number A. Such decays are
called β–decays. Reactions producing unstable nuclei are for instance fusion reaction of neutrons or
protons with stable nuclei—such processes are also called capture reactions.
mechanism that is based on the reactions starting from the proton-capture reactions. Because of the repulsing Coulomb
stable seed of the neutron-induced production processes force, such reactions become less and less probable as the
(Figure 2). mass, hence the charge, of the heavy reaction partners in-
There are two major reactions chains transforming the crease. The stellar reaction rate depends on the reaction rate
stable, neutron-rich seed into a proton-rich composition per particle pair and the density of the stellar matter. Both,
[5]. The first originally discussed mechanism is based on temperature and density must be very high to allow such a
Figure 2. Chart of stable nuclides between zinc (Z = 30) and bismuth (Z = 83). Only a few combinations of neutrons and
protons can form a stable nucleus. Those nuclei, which have roughly the same number of protons and neutrons, form the
valley of stability. The p nuclei (colored) are on the proton-rich (or neutron-deficient) side of the valley of stability. The two
lightest stable isotopes of molybdenum, 92,94Mo, are p nuclei. The p nuclei of ruthenium, 96,98Ru, mark the end of the mass
range where proton capture reactions can contribute significantly to the element production. The Coulomb barrier of the
heavier nuclei, which needs to be penetrated to allow a nuclear reaction, is too high. Gamma-induced reactions are there-
fore the main mechanism, which transforms matter originating from neutron-induced processes into proton-rich matter.
Vol. 26, No. 4, 2016, Nuclear Physics News 15You can also read
