6th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Sunday–Friday, November 26–December 1 2023;
Hawaii, the Big Island
Session 3WHB: Fragment Separation at RIBF and FRIB and Rare Isotope Production Mechanisms II
Invited Workshop
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Chair: Hiroyoshi Sakurai
Room: Hilton Waikoloa Village Kohala 1
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Monday, November 27, 2023
11:00AM - 11:30AM
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3WHB.00001: Studies of the two-step scheme for new RI-beam production in the medium-heavy very-neutron-rich region
Invited Speaker:
Hiroshi Suzuki
Two studies about the “two-step scheme” performed at BigRIPS in RI Beam Factory will be presented.
The first one is an investigation of usefulness of the two-step scheme [1], which was proposed [2] for an efficient production of medium-heavy very-neutron-rich radioactive isotopes (RI) as an alternative method to the in-flight fission of 238U (one-step scheme). The one-step scheme is expected to be limited soon: Production cross sections for the very neutron-rich RIs have been drastically decrease with neutron numbers (N). The two-step method may produce more exotic RIs by the following two steps: In the first step, a long-lived neutron-rich RI (e.g. 132Sn) is produced by ISOL and post-accelerated, then, more exotic RI (e.g. 128Pd) is produced by fragmentation in the second step. To evaluate its usefulness, we have measured the cross sections of very neutron-rich Pd isotopes produced from a 132Sn beam and compared their estimated yields by the two- and one-step schemes under an assumption of 1-MW beam facilities. This comparison suggests that the two-step scheme with 132Sn provides yields >40-times higher than those by the one-step scheme for very neutron-rich N = 82 region. Moreover, we examined which scheme is better to produce RIs at each region in the nuclear chart by using various long-lived RI beams supplied from ISOL in the two-step scheme.
The other one is about a new RI-beam production/separation method in BigRIPS, “in-separator two-step method” [3], which could have an advantage for obtaining yields of very neutron-rich RIs compared to the in-flight fission of 238U. In the proposed new method, less-exotic intermediate RI is produced in the 1st stage and more-exotic objective RI is produced and separated in the 2nd stage. The experimental results with 133Sn as the intermediate RI will be shown.
References
[1] H. Suzuki et al., Phys. Rev. C 102 (2020) 064615.
[2] K. Helariutta et al., Eur. Phys. J. A 17 (2003) 181.
[3] H. Suzuki et al., RIKEN Acc. Prog. Rep. 55 (2021) S7. |
Monday, November 27, 2023
11:30AM - 12:00PM
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3WHB.00002: New techniques for isotope identification and separation of BigRIPS
Invited Speaker:
Toshiyuki Sumikama
The RI beam factory (RIBF) accelerates primary beams from hydrogen to uranium to 345 MeV/u and produces RI beams by using the in-flight fragment separator BigRIPS. As RI beams get heavier or slower, the isotope separation and particle identification (PID) with BigRIPS become more difficult, since the charge state Q of the RI beams could be easily changed in materials and detectors used for the separation and PID. We have developed these RI beams to enable experiments in new regions in terms of energy and mass.
Experiments with slowed-down RI beams have been already conducted at the OEDO beamline constructed by CNS in cooperation with RIKEN. We introduce RIKEN's early development of beam tuning technology and new PID of secondary-reaction products at 50 MeV/u. The multi-sampling ionization chamber (MUSIC) was used to measure ΔE, E, and range for the first time. The energy measurement at the lower energy was the suggestive data for PID in the heavy regions in terms of the Q fluctuation in the detector.
To purity the heavy RI beam with the uranium primary beam, fission fragments must be considered. We found that the separation figure for each Q was powerful to consider the separation of the fission fragments from the heavy RI beam. The experiment to produce the 208Rn beam will be presented. The Z resolution of 208Rn and the energy measurement at the 50-MeV/u PID helped us to find that a poor Z resolution due to the Q fluctuation could be improved by a small difference of the cross section of the Q change. The MUSIC detector with the Xe-based gas was found to be promising for the Z identification, of which data will be presented by Yoshimoto et al. in a different workshop. |
Monday, November 27, 2023
12:00PM - 12:30PM
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3WHB.00003: Observation of new isotopes at FRIB, and reaction mechanisms for exotic nuclei production
Invited Speaker:
Oleg B Tarasov
The Facility for Rare Isotope Beams (FRIB) at Michigan State University (MSU) is a new facility based on a superconducting linear accelerator with a wide array of primary beams around 200 MeV/u, which allows some flexibility in rare isotope production. The experimental program at FRIB began in May 2022, and in this report, I present the first observations of new isotopes using a 198Pt beam. Additionally, I will focus on investigating the reaction mechanisms involved in the production of unstable isotopes located far from stability, which helps determine with primary beam to use and what the extent of isotopes can be produced.
Statistical models, such as the abrasion-ablation (AA) or intra-nuclear cascade (INC) models, have shown good agreement with experimental data [1]. A multi-step reaction scheme has been found to be an effective approach for exploring the neutron-rich region [2], supported by experimental results [3,4]. In this context, I will discuss the key requirements for qualitatively predicting production cross sections for unknown isotopes using the AA model, taking into account the multi-step reaction scheme. The discussion will encompass advancements in theoretical and experimental studies, as well as computing.
1. O. B. Tarasov et al., Phys. Rev. C 87, 054612 (2013)
2. L.Neufcourt et al., Phys. Rev. C 101, 044307 (2020).
3. H. Suzuki et al., Phys. Rev. C 102, 064615 (2020).
4. O. B. Tarasov et al., Phys. Rev. Lett. 122, 022501 (2018).
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