Bulletin of the American Physical Society
5th Joint Meeting of the APS Division of Nuclear Physics and the Physical Society of Japan
Volume 63, Number 12
Tuesday–Saturday, October 23–27, 2018; Waikoloa, Hawaii
Session 2WJB: Surrogate Techniques for Neutron-induced Reactions on Radioactive Nuclei for Fundamental and Applied Nuclear Science II |
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Chair: Jolie Cizewski, Rutgers Univesity Room: Hilton Kona 5 |
Tuesday, October 23, 2018 4:00PM - 4:30PM |
2WJB.00001: 79Se(d,p)80Se reaction as a surrogate for (n,g) reaction of the long-lived fission product of 79Se Invited Speaker: Nobu Imai 79Se is one of the long-lived fission products (LLFPs) of the nuclear waste. The half-life is as long as 3.3x105 years. Though the LLFPs are considered to be stored in the deep geological repository, the site has not been determined in the most of countries in the world. Seeking for a way to transmute such nuclei is expected for our descendants. Considering that the mean free path and the cross sections, the neutron induced reactions, such as (n,g) reaction, are promising for the transmutation. 79Se is also important astrophysically because it is located on the path of s-process nucleosynthesis. This nucleus plays as a role of a cosmo chronometer. However the neutron capture reaction on the nucleus has not been experimentally evaluated partly because the selenium is toxic and the 79Se is radioactive. 77,79Se(d,p)78,80Se reactions were measured in inverse kinematics as surrogate reactions of 77,79Se(n,g)78,80Se, respectively. There is the experimental data of 77Se(n,g)78Se at 550 keV. The evaluated cross section of 77Se(n,g)78Se reaction from (d,p) reaction was used to verify the technique. The experiment was carried out at the new energy degrading beam line name OEDO in RIBF. The 77,79Se beams of about 20 MeV/nucleon were focused by OEDO on a secondary target of 4 mg/cm2 thick CD2 target. The excitation energy of the final state was determined by measuring the scattering angles and the energy of the recoiled proton by 6 telescopes of SSDs and CsI(Tl) placed in the backward angle. The residual nuclei were identified by the spectrometer which enabled us to determine the gamma emission channel without measuring the gamma rays. In this talk, the detailed experimental setup and the result of the evaluated cross section of 77,79Se(d,p)78,80Se reactions will be presented. |
Tuesday, October 23, 2018 4:30PM - 5:00PM |
2WJB.00002: Surrogate reactions for neutron-induced fission reaction and neutron capture reaction by heavy ion transfer reaction Invited Speaker: Hiroyuki Makii A project of the fission data measurement (cross sections, fragment mass distribution, total kinetic energy, and neutron multiplicities) as well as the measurement of the neutron capture cross sections, using a surrogate method based on multi-nucleon transfer reactions induced by heavy-ion projectile, is running at Japan Atomic Energy Agency (JAEA). We have constructed appatus consists of a fission setup including four position-sensitive multi-wire proportional counters (MWPCs) to detect fission fragments and a capture setup containing two anti-Compton LaBr3(Ce) spectrometers to measure the γ-rays from the populated compound nuclei. Both setups contain a Si ΔE-E detector system to detect outgoing projectile-like particles by which we can indentify the populated compound nuclei. We also placed 33 scintillators around the fission setup to detect fission neutrons in coincidence with the fission fragments. The measurements was carried out at the JAEA-Tokai tandem accelerator facility. Reactions of 18O projectile on actinide targets such as 232Th, 238U, and 248Cm were used to measure the fission data. For the measurement of the nuetron capture cross sections, we used multi-nucleon transfer channels of 155, 157Gd + 18O and 90, 92Zr + 18O reactions. In this contribution, we will present our results on neutron-induced fission and neutron capture cross sections by using the surrogate method. |
Tuesday, October 23, 2018 5:00PM - 5:30PM |
2WJB.00003: Theoretical assessment on the validity of the surrogate technique Invited Speaker: Satoshi Chiba Surrogate method is an important methodology to determine nuclear reaction properties for which direct measurements are practically impossible, such as neutron-induced cross sections of short-lived isotopes. In the surrogate method, the same compound nucleus as the desired reaction is populated by different combination of target and projectile, and decay branching ratios are measured. This information will be combined with population probability of the desired reaction to get information on what we need. Such a method is associated with uncertainties. The biggest one is the mismatch of angular momentum distribution between the desired and surrogate reactions. We propose a way to compensate for this difference in the surrogate "ratio" method, where the decay branching ratios are determined relative to those of known reactions. The idea is to use 2 reactions having very similar properties in terms of nuclear structure and reaction mechanisms. If the 2 reaction populate the compound nuclei with identical spin distributions, we can prove that the "ratio of branching ratios" does not depend on the spin distribution noticeably. This is a good way to assess validation of the surrogate "ratio" method without knowing the underlying reaction mechanisms in detail. Recently, a group in JAEA is actively pursuing the surrogate method using $^{18}$O projectile on heavy nuclei, $^{232}$Th, $^{238}$U, $^{242}$Cm and $^{254}$Es, to extract fission properties such as mass distribution of fission fragments over many populated compound nuclei, and Langevin theory is applied to analyze the data. In this analysis, however, we need detailed knowledge on the population mechanisms of each compound nucleus, which are populated by multinucleon transfer reactions. Especially, the spin distribution of each compound nucleus at specific excitation energy bin must be properly understood. We will present our resent analysis based on antisymmetrized molecular dynamics.
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