North American Storage Rings & Neutron Captures Workshop

28 Jun 2021, 07:30 → 30 Jun 2021, 12:00 US/Pacific

Virtual

Aaron Couture (LANL), Annika Lennarz (TRIUMF), Artemis Spyrou (NSCL/FRIB/MSU), Chris Ruiz (TRIUMF), Iris Dillmann (TRIUMF), Rene Reifarth (Goethe Uni Frankfurt), Sean Liddick (NSCL/FRIB/MSU), Shea Morgan Mosby (LANL)

Rare-isotope storage rings offer unique capabilities to study nuclear properties through their relatively long storage times, as has been demonstrated by the work that has been performed over the last several decades at ring facilities around the world. Despite these opportunities, to date little investment has been made in North America in rare-isotope storage ring capabilities.

Neutron-induced reactions play a key role in understanding such diverse scientific fields as nuclear astrophysics, stockpile stewardship, reactor performance, and nuclear forensics. For many of these endeavors, reactions on short-lived nuclei offer key insights into the physical environment. Neutron reactions on short-lived nuclei have presented particular challenges, however, as both beam and target are unstable. Bringing storage rings to bear on the challenges of neutron-induced reactions offers the opportunity to directly measure neutron-induced cross sections.

In order to develop the technical capabilities to make this opportunity a reality, we invite you to participate in a virtual workshop focused on the scientific opportunities as well as the enabling technologies for such a new research avenue.

Presently, in North America three independent projects are discussed that aim to measure direct neutron capture cross sections of short-lived nuclei. The LANL project follows the proposal of combining a spallation neutron target fed by the 800 MeV proton beam from the LANSCE facility with a storage ring. The TRIUMF Storage Ring project will use radioactive beams from the existing ISAC facility and proposes to install a high-intensity neutron generator in a low-energy storage ring. The FRIB proposal would use the ReA3/6 beams and potential higher energy upgrades. All three projects are largely complementary and are running on different time scales and projected costs.

This workshop will bring together interested scientists and inform the community about these exciting future plans. It will initiate various collaborative working groups to work on common designs and detector concepts. Plenty of time will be available for discussions and break-out sessions or spontaneous discussions. Embracing the virtual nature of the workshop, the meeting will be broken into three half-day sessions. No parallel sessions are planned. Zoom will be used for the primary presentation of technical content, while Gather.Town allows us to invite you for a virtual coffee and exciting discussions.

This workshop is supported by IReNA, the International Research Network for Nuclear Astrophysics . IReNA is a US National Science Foundation AccelNet Network of Networks. It ​connects six interdisciplinary research networks across 17 countries to foster collaboration, complement and enhance research capabilities in the US and abroad, and thus greatly accelerate progress in science. It covers the Focus Areas FA1 (Nuclear Reaction Rates), FA4 (r-process experiments), and FA6 (Nuclear Data).

Gather.Town_QuickGuide.pdf

First Circular First Circular

Presentations

• Bernstein_TRIUMF_Storage_Ring_Workshop_talk_2021-v2.pdf
• CGBruno_CARME.pdf
• FRIB Storage Ring Ideation.pdf
• glorius.pdf
• GRIESER_TRIUMF_workshop.pdf
• Intro_Dillmann.pdf
• Litvinov_20210628_NA_Storage_Rings.pdf
• Massimi_NASR&NC.pdf
• NG Trap Mardor neutron capture workshop 202106 website.pdf
• northamerican_rings_jurado_short.pdf
• reifarth_neutron_target_NA_rings.pdf
• sanjari_northamerican.pdf
• smosby_nar_lanlproj_2021.pdf
• Surman.pdf
• TRISR-Dillmann2021.pdf
• WorkingGroup1.pdf
• WorkingGroup2_ID.pdf

Monday, 28 June

Introduction 1

1 Welcome and Introduction

2 Neutron capture in Astrophysics

Neutron capture processes are responsible for the astrophysical synthesis of the vast majority of nuclear species heavier than iron. Here we review the major neutron capture nucleosynthesis processes - the s, i, and r processes - and highlight how reductions in individual neutron capture rate uncertainties are crucial for our understanding of each process.

Speaker: Rebecca Surman (U Notre Dame)

3 Fast Neutron Sources for Applications

Speaker: Lee Bernstein (LBNL/ UC Berkeley)

08:45 Break

Introduction 2

4 Technological challenges at low-energy storage rings

Speaker: Prof. Yuri A. Litvinov (GSI Darmstadt and University of Heidelberg)

5 Neutron-induced reactions in inverse kinematics

Speaker: Rene Reifarth (Goethe Uni Frankfurt)

6 A new HIE-ISOLDE Storage Ring

A heavy ion storage ring at the HIE-ISOLDE facility offers the opportunity for the first time to do experiment with stored secondary ion beams. The planned physics program is rich and varied, ranging from the investigations of
nuclear ground state properties to reaction studies with astrophysical relevance. In addition to experiments performed using beams circulating within the ring, electron cooled ion beams can also be extracted and exploited by external spectrometers for high-precision measurements.
The Max-Plank Institute for Nuclear Physics has offered the TSR ring, which was installed at the Max Planck Institute for nuclear physics in Heidelberg, for installation at the HIE-Isolde facility at CERN. The physics case for this has been discussed in various workshops and scientific committees at CERN who have strongly endorsed the scientific case. However, the final decision by the CERN directorate on the TSR @ ISOLDE project has been postponed until the LHC's second upgrade program has been completed. Without the approval of the TSR project by CERN, the Max Planck Institute could no longer hold the storage ring, so the TSR was finally scrapped.
Due to the importance of a storage ring at ISOLDE, which is more suitable for nuclear physics experiments than the TSR, a new storage ring design was created. The design criteria for the new storage ring, called ISR hereafter, are summarized below.
The storage ring should be able to store ions up to $^{238}$U and 10 MeV/u with the equilibrium charge state available with the HIE-ISOLDE stripper.
This means that the ring must be designed for a maximum beam rigidity of 1.5 Tm. Daughter nuclei that are created in nuclear reactions with the gas target often have very large transverse momenta and should be focused in the detector positions, so that the spectrometer of the new storage ring must have focal points in the detector planes.
The storage of daughter nuclei, which are created in (p, $\gamma$) reactions, should be possible up to a certain rigidity deviation to the main beam so that the daughter nuclei can be separated from stripped ions with the help of electron cooling. Furthermore, it should be possible to extract an ion beam which has the properties of an electron cooled ion beam. Technical details of the new planned ring facility will be discussed.

Speaker: Dr Manfred Grieser (Max-Planck-Institut für Kernphysik)

7 Direct neutron capture cross section measurements of trapped short-lived isotopes at SARAF-II

Direct measurements of neutron capture cross sections of short-lived isotopes, especially in the neutron-rich realm, are of vast interest to nuclear physics and astrophysics, but are currently impossible due to the instability of both projectile and targets. We propose a concept of such measurements for thermal (or cold) neutrons at Phase-II the Soreq Applied Research Accelerator Facility (SARAF-II), currently under construction in Yavne, Israel. SARAF-II will have the unique capability to produce a world-competitive rate of fission fragments and high-flux neutron beams in the same facility [1], making it an optimal site for such measurements.
Neutron-rich isotopes will be produced by neutron-induced fission of thin actinide targets and thermalized in a cryogenic gas-filled stopping cell. They will be extracted and mass-separated in an RFQ beam-line, and isotopes of a specific isobar chain will be accumulated in a special RF linear trap. The SARAF-II ion beam will then be diverted to a different target, which will produce thermal or cold neutrons that will irradiate the trapped neutron-rich isotopes. Using thermal or cold neutrons will enable us to guide and focus the neutrons onto the isotope cloud inside the trap, optimizing the reaction rate. The isotopes that capture a neutron will be ejected to a multiple-reflection time-of-flight mass-spectrometer (MR-TOF-MS), which is precise enough to identify them unambiguously by their mass. The overall ratio between the amounts of a specific A+1 isotopes and their A predecessors will provide the neutron capture cross section of each of the different A isotopes.
For the above system, our preliminary estimations indicate a rate of a few events/day/barn, for isotopes with half-lives down to the range of tens of minutes. Due to the cleanliness of our measurement that is basically background free, such a rate should be detectable. Based on theoretical cross section estimations, tens of new cross sections of unstable isotopes may be measured. In addition, we may discover more isotopes with surprisingly high neutron capture cross sections (see, e.g., [2]), which current theoretical cross-sections convolved with their fission yield render undetectable with our method.
The isotope-target trap will have to contain isotope kinetic energies of up to a few hundred eV due to ongoing beta decay in the trap and the recoil of the A+1 isotopes following thermal or cold neutron capture. We will present a conceptual design of such a trap, and possible ejection methods that single out A+1 isotopes with respect to A. Experimental tests of the maximal isotope storage amount and trapping duration will be performed in the near future on the triple-RFQ trapping system developed at Justus-Liebig-University Giessen, Germany [3].

[1] I. Mardor et al., Eur. Phys. Jour. A 54: 91 (2018)
[2] J. A. Shusterman et al., Nature 565, 328 (2019)
[3] E. Haettner et al. Nucl. Instr. Meth. A 880, 138 (2018)

Speakers: Israel Mardor (Tel Aviv University), Dr Timo Dickel (GSI Helmholtzzentrum für Schwerionenforschung)

10:55 Gather.Town Afterglow

https://gather.town/i/65cgFHeU

Tuesday, 29 June

Session 3

8 Storage Ring Proj. LANL

Speaker: Shea Morgan Mosby (LANL)

9 Storage Ring Proj. TRIUMF

Speaker: Dr Iris Dillmann (TRIUMF)

TRISR-Dillmann2021.pdf

10 Storage Ring Proj. FRIB

Speaker: Georg Bollen (FRIB/MSU)

11 Surrogate reactions at ion storage rings

The surrogate-reaction method is a powerful method to indirectly infer neutron-induced cross sections of very short-lived nuclei. When the surrogate method is used in inverse kinematics, the nucleus formed in the neutron-induced reaction of interest is produced by a reaction (typically a transfer or an inelastic-scattering reaction) involving a radioactive heavy-ion beam and a stable, light target nucleus. The decay probabilities (for fission, neutron and gamma-ray emission) as a function of excitation energy of the nucleus produced by the surrogate reaction provide precious information to constrain models and enable much more accurate predictions of the desired neutron-induced cross sections [1].

Yet, the full development of the surrogate method is hampered by the numerous long-standing target issues. The objective of our project is to solve these issues by combining surrogate reactions in inverse kinematics with the unique and largely unexplored possibilities at heavy-ion storage rings. In this contribution, I will present the conceptual idea of the setup, which will be developed to measure for the first time simultaneously the fission, neutron and gamma-ray emission probabilities at the storage rings of the GSI/FAIR facility. I will also discuss the technical developments that are being carried out towards these measurements.

[1] R. Pérez Sánchez, B. Jurado et al., Phys. Rev. Lett. 125 (2020) 122502

Speaker: Beatriz Jurado (CENBG Bordeaux)

12 Nuclear reaction studies using CARME @ CRYRING

Measurement of nuclear reactions involving radioactive isotopes is critical to model and understand the wealth of new astronomical data from stellar explosions. At FAIR@GSI (Germany), the newly commissioned low-energy CRYRING storage ring offers novel possibilities for nuclear physics and nuclear astrophysics reaction studies.

I will describe initial commissioning, present status and approved science plans for CARME (CRYRING Array for Reaction MEasurements), a novel detection array for nuclear and atomic reaction measurements soon to be installed on the CRYRING. CARME features moving double-sided silicon strip detectors, compatible with the extreme high vacuum conditions of the CRYRING, affording high efficiency and angular resolution for charged-particle detection. CARME @ CRYRING offers the possibility to study nuclear reactions in a range of astrophysical scenarios, ranging from the Big Bang to supernovae, using both stable and radioactive beams.

Speaker: Carlo Bruno (The University of Edinburgh)

09:05 Break

Session 4

13 Physics, Astrophysics and advanced nuclear technologies at CERN n_TOF: present and future

The neutron time-of-flight facility n_TOF at CERN has been producing relevant nuclear data for science and technology since 2001. More in detail, neutron-induced reaction cross sections of interest to: 1. Astrophysics (both Big Bang and stellar Nucleosynthesis); 2. emerging nuclear technology and related safety (fission and fusion as well as transmutation of nuclear waste); 3. Neutron capture therapy (treatment of cancer with neutrons) and 3. basic Nuclear Physics (nuclear interaction, nuclear structure effects on fission, excited states) have been reported on more than 100 isotopes, so far.

After two years of facility upgrades, the scientific program will restart this summer. Several challenging time-of-flight experiments are foreseen on stable and radioactive samples in the two existing measurement stations. In particular, the 185 m beam line feeds the first experimental area (EAR1), where high-resolution measurements can be performed. While EAR2, placed approximately 20 m on top of the spallation target, provides a factor 50 higher neutron flux, while maintaining a good energy resolution. In this contribution I will present a selection of physics cases together with the related experimental setup. In fact, several detection systems are currently available at n_TOF for radiative capture, fission and charged particle (in the exit channel) reactions.

Finally, I will present some ideas of possible future experiments that could become feasible thanks to the availability of a new irradiation station (named NEAR station) now being built close to the neutron-producing target. The possibility to produce sample material at the present or upgraded ISOLDE facility and then irradiated at the NEAR station will represent, therefore, a great opportunity for synergy between these two CERN facilities.

Speaker: Cristian Massimi (INFN and University of Bologna)

14 Proton-induced reactions on stored radioactive ions

In the last years, a novel technique to study proton-induced reactions on post-decelerated ions has been established in the ESR heavy ion storage ring at GSI.
Very recently this technique has been employed to measure the proton capture cross section on radioactive 118Te ions after in-flight production in the fragment separator FRS.
This contribution gives a summary of the recent developments and achievements as well as an outlook to the future of the experimental campaign.

Speaker: Jan Glorius (GSI Helmholtz Center Darmstadt)

15 Electromagnetic detectors for experiments in heavy ion storage rings

Nuclear astrophysics studies on highly charged radionuclides benefit from accelerator facilities with storage rings, where exotic nuclides produced with small yields can be stored efficiently. Non-destructive detection methods are often used for in-flight measurements based on frequency analysis of the signal from the detector, leading to precision results for mass and lifetime of exotic nuclear species or isomeric states. The sensitivity of such detection systems is of primary importance, specially when the number of stored ions is small. Furthermore, since the exotic nuclides of interest are by nature short-lived, the detectors must be fast.

In this talk we would like to highlight some of the current activities and challenges with regard to the development and application of such detectors in past and future experiments in storage rings.

Speaker: Dr Shahab Sanjari (GSI Darmstadt and Aachen University of Applied Sciences)

16 New ideas and missing thoughts

Moderated discussion

Speaker: Artemis Spyrou (NSCL/FRIB/MSU)

10:50 Gather.Town Afterglow

https://gather.town/i/65cgFHeU

Wednesday, 30 June

Working Group 1: Neutron production and moderation

Aaron Couture and Shea Mosby

Working Group 2: In-ring detection methods

Iris Dillmann and Shea Mosby

09:00 Break

Working Group 3: Recoil extraction

Annika Lennarz and Chris Ruiz

Summary & Close-Out

11:00 Gather.Town Afterglow

https://gather.town/i/65cgFHeU