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佐々木 悠人; 岩本 信之; 前田 茂貴; 高木 直行*
no journal, ,
我が国では、既存の核分裂炉を用いた医療用放射性同位元素(RI)製造のための国内態勢の整備・実現に向けた研究が進められている。濃縮ウラン(HEU, LEU)を原料としない
Mo/
Tcの製造方法として、高速実験炉「常陽」の炉心周辺に設置される中性子減速場を利用した中性子放射化法による効率的なMoの製造を検討した。その結果、ベリリウム充填率60%の中性子減速集合体を用いて照射場で7日間照射することにより、231
33TBqのMoを製造できることがわかった。この量は、2週間に1回の供給を考慮しても、国内の1週間分の需要をまかなえる量である。しかし、常陽は年1回の検査で生産継続が難しいため、他の研究炉や加速器とのベストミックスによる供給体制を確立すれば、安定供給は可能であろう。
西尾 勝久
no journal, ,
We have promoted study of fission using multinucleon transfer (MNT) reactions. The reaction allows us to study fission of many nuclei, including neutron-rich nuclei, which cannot be populated by other reactions. Also, excitation energy (E*) of compound nucleus distributes widely, which can be used to investigate excitation-energy dependence of fission. The experiments were carried out at the JAEA tandem accelerator facility using 
O beam and various radioactive target nuclei. It was demonstrated that data fission-fragment mass distributions (FFMDs) for more than 20 nuclides were obtained in one reaction, and their excitation energy dependence up to E*=60 MeV was derived. The measured FFMDs were explained only by taking into account the multi-chance fission, i.e. fission after neutron emission. From the threshold of the excitation function of fission probably, fission barrier height was derived.
牧井 宏之; 西尾 勝久; Orlandi, R.; 廣瀬 健太郎; 浅井 雅人; 洲嵜 ふみ; Smallcombe, J.
no journal, ,
A new measurement system is under development to simultaneously determine (
), (
), (
), and (
) reaction cross sections via the surrogate reaction method. The system comprises LaBr
(Ce) scintillators for high-energy 
rays, Ge detectors for low-energy discrete rays, Si detectors for scattered particles, and solar cell detectors for fission fragment measurements. This setup will enable future investigations of pre-fission neutron emission, known as multichance fission. To evaluate the system's performance, we irradiated a 
Am target with a 
He beam at the JAEA-Tokai tandem accelerator facility, observing scattered particles, rays, and fission fragments from the compound nuclei produced in the He-induced reactions. In this presentation, we will discuss the details of the developed system and present the results of the test experiment.
小浦 寛之
no journal, ,
There are some decay modes of nuclei in the nuclear chart. This is mainly due to the competition between the beta-decay, and particle emissions as alpha-decay or proton emission, especially in the heavy and neutron deficient nuclear mass region. The fission decay process additionally plays an important roll to nuclear decays in the heavy and super heavy mass region. We discuss the global properties of each decay as alpha- decay, beta-decay, proton emission, and fission from the mass-model calculation, the KTUY mass model. The beta-accompanying process as beta-delayed neutron emission and beta-delayed fission will also be discussed, which is related to the r-process nucleosynthesis in stars. The coexistence of alpha-decay, proton emission. and fission is estimated in the A~230 of neutron-deficient region, for examples.
洲嵜 ふみ; 西尾 勝久; 牧井 宏之; 廣瀬 健太郎; Orlandi, R.; Smallcombe, J.
no journal, ,
Multinucleon transfer (MNT) reaction attracts interest in the field of nuclear physics and astronomical nucleosynthesis as it can produce neutron-rich heavy and superheavy nuclei. On the other hand, the reaction process is not well understood, making it difficult to find the optimal target-projectile combination and reaction energy. In order to create a reliable theoretical model, it is important to obtain detailed experimental data. We have started to measure cross sections of evaporation residues (ERs) produced in MNT reactions using the recoil mass separator, JAEA-RMS. Taking advantage of a feature that JAEA-RMS can easily rotate (0 - 40 degrees) around the target chamber, we can separate ERs at finite recoil angles. We established the on-line alpha-decay measurement at the focal plane Si detector to identify produced nuclides, and their cross sections were measured as a function of recoil angle. This result is the first to realize the on-line decay measurement ERs produced by the MNT reactions at a finite angle. The transported ERs changed largely with respect to electrostatic and magnetic rigidity given to RMS. In the studied reaction 
Si + 
Bi, it is found that isomeric state with higher spins is produced with larger cross sections than low-spin ground state for 
At and 
Fr.
荒木 祥平; 吉川 智輝; 新垣 優; 神川 豊; 長谷川 健太; 多田 裕太; 住谷 正人; 関 真和; 會澤 栄寿; 石井 淳一; et al.
no journal, ,
燃料デブリには原子炉構造材である鉄やコンクリートが含まれていると考えられるため、臨界管理における解析手法の妥当性確認のためには、これらの主要成分であるFeやSi、Caといった核種を炉心に直接装荷して取得した臨界実験データの新規取得が必要である。本研究では、中性子吸収効果の大きく臨界安全性に大きな影響があると考えられるFeに着目し、STACY更新炉における臨界実験を実施した。実験においては、炉心に燃料棒と同じサイズのステンレス棒を装荷し、燃料棒及びステンレス棒の位置と本数を変えて複数の臨界水位を測定した。これらの実験データはJEDNL-5をはじめとする核データライブラリを用いて解析し、核データライブラリの検証を行った。発表においては実験データ及び解析結果を示す。
岡田 和記; 西尾 勝久; 和田 隆宏*; Carjan, N.*
no journal, ,
The dynamical approach to fission using the multi-dimensional Langevin equation has been widely used for calculations of the fission process. This approach provides the fragment mass and total kinetic energy (TKE) distributions, which can be directly compared with experimental data across systems with various excitation energies. Recent measurements for the fission of 
Md conducted at JAEA indicate that the mass-TKE distributions consist of multiple distinct fission modes: short symmetric, asymmetric, and super-long symmetric fission. To understand these observations, dynamical calculations using the high-dimensional Langevin equation play an important role. In this study, we calculate the fission process of Md by solving the six-dimensional Langevin equation with Cassini shape parameterization. To describe various fission modes, we employ six Cassini shape parameters 
as the collective coordinates.