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O+
Np reactionVermeulen, M. J.; 西尾 勝久; 廣瀬 健太郎; Kean, K. R.; 牧井 宏之; Orlandi, R.; 塚田 和明; Tsekhanovich, I.*; Andreyev, A. N.; 石崎 翔馬*; et al.
Physical Review C, 102(5), p.054610_1 - 054610_11, 2020/11
被引用回数：5 パーセンタイル：52.72(Physics, Nuclear)Fission fragment mass distributions for 23 nuclei (
U, 
Np, 
Pu, 
Am, 
Cm, and 
Bk) were measured using the multi-nucleon transfer approach in the reaction of O+Np, and their excitation-energy dependence was obtained up to a maximum of 70 MeV. Among them, the low energy fission of 
Np, 
Pu, and 
Cm is reported for the first time. The experimental data for all the studied nuclei were compared to the Langevin calculations. The calculation which takes into account the effects of multi-chance fission well reproduced the peak-to-valley ratio and mass-asymmetric peak positions of the distributions. The angular momenta given to the fissioning nucleus is also discussed.
田中 翔也; 有友 嘉浩*; 宮本 裕也*; 廣瀬 健太郎; 西尾 勝久
Physical Review C, 100(6), p.064605_1 - 064605_6, 2019/12
被引用回数：13 パーセンタイル：79.29(Physics, Nuclear)散逸揺動定理を採用した動力学模型を使用し、
U, 
Np, 
Pu (
=15-55MeV)という広い範囲の核種および励起エネルギーにおいて核分裂片質量分布の評価を行った。本研究の特色は、原子核が分裂へ至るまでに中性子を放出するという、マルチチャンス核分裂の概念を理論計算へ導入していることである。その結果、実験データを系統的に再現する計算結果を得られた。特に、励起エネルギーが高い領域においても核分裂片質量分布がふた山構造を維持する傾向や、原子核の初期状態(特に中性子数)に依存するという実験データの傾向を再現することに成功した。またこの傾向が、核分裂前の中性子放出確率を支配している複合核の中性子結合エネルギーと相関を持つことを示した。
西尾 勝久; 千葉 敏*
日本原子力学会誌ATOMO
, 59(12), p.717 - 721, 2017/12
核分裂は原子力エネルギー利用の基礎となる現象であるが、その複雑さのため質および量ともに限られた実験データを現象論によって記述し、核データとして利用されるにとどまっていた。近年、新規の実験技術確立に加え高性能計算機を活かした理論計算に大きな進展があったので、最新成果を見ながら議論する。
西尾 勝久; 廣瀬 健太郎; Vermeulen, M. J.; 牧井 宏之; Orlandi, R.; 塚田 和明; 浅井 雅人; 豊嶋 厚史; 佐藤 哲也; 永目 諭一郎; et al.
EPJ Web of Conferences, 163, p.00041_1 - 00041_6, 2017/11
被引用回数：1 パーセンタイル：61.21(Nuclear Science & Technology)We are promoting a study of fission using multi-nucleon transfer (MNT) reactions, where excited states in neutron-rich actinide nuclei, which cannot be accessed by particle capture and/or fusion reactions, are populated. Also, the excited states in the fissioning nucleus are widely populated by the MNT reactions, from which effects of excitation energy on fission properties can be investigated. Experiments were carried out at the JAEA tandem facility in Tokai, Japan. We studied reactions using the O beam and several actinide target nuclei such as 
Th, U, Np, 
Cm. Ejectile nucleus was identified by a silicon 
E-E telescope to identify transfer channel and hence the compound nucleus. Fission fragments were detected by multi-wire proportional counters, and fission fragment mass distributions (FFMDs) were measured for each isotope. Measured FFMDs are reproduced by a calculation based on the fluctuation-dissipation model, and importance of multi-chance fission concept is investigated. Fission fragment angular distribution relative to the recoil direction suggested the increase of the spin of the fissioning nucleus with the number of transferred nucleons.
西尾 勝久; 廣瀬 健太郎; L
guillon, R.; 牧井 宏之; 西中 一朗; Orlandi, R.; Smallcombe, J.; 千葉 敏*; 荒木 祥平*; 渡辺 幸信*; et al.
no journal, ,
We report the recent development for the fission study using multi-nucleon transfer reaction at the JAEA tandem facility. Using multi-nucleon transfer reaction, neutron-rich nuclei can be produced, which cannot be accessed by fusion-reaction, and several nuclei populated by different transfer channels can be studied in one experiment. Another feature of transfer reaction is that the excitation energy of a compound nucleus is populated from the ground state up to several tens MeV, thus the excitation energy dependence of the fission properties can be obtained. We have carried out experiments in the reactions of O + U and O + Th. Transfer channel and the excitation energy of compound nucleus were determined by using silicon E-E detectors. Fission fragments were detected by position-sensitive multi-wire proportional counters. We obtained the fragment mass distributions from actinium to plutonium isotopes for 24 nuclei and their excitation energy dependence. Among them, fragment mass distributions for nine nuclei were obtained for the first time.
西尾 勝久; 廣瀬 健太郎; Lguillon, R.; 牧井 宏之; 西中 一朗; Orlandi, R.; Smallcombe, J.; 千葉 敏*; 荒木 祥平*; 渡辺 幸信*; et al.
no journal, ,
Recent development of the fission study using multi-nucleon transfer reaction at the JAEA tandem facility will be presented. Using multi-nucleon transfer reaction, wide variety of nuclei around the target nucleus is produced. By identifying transfer channel, fission properties of several compound nuclei can be studied in one experiment. Another feature of transfer reaction is that excitation energy of a compound nucleus can be populated continuously from the ground state up to several tens MeV, allowing us to study the excitation energy dependence of fission properties. Experiments were carried out in the reactions of O + U and O + Th. Transfer channel and the excitation energy of the compound nucleus were determined by using silicon E-E detectors. Fission fragments are detected by position-sensitive multi-wire proportional counters. Results for fission fragment mass distributions for more than 20 nuclei and their excitation energy dependence will be discussed.
西尾 勝久; 廣瀬 健太郎; Lguillon, R.; Orlandi, R.; 西中 一朗; Smallcombe, J.*; 千葉 敏; 荒木 祥平*; 渡辺 幸信*; 立澤 遼太郎*; et al.
no journal, ,
A recent development of fission study using multi-nucleon transfer reaction at the JAEA tandem facility will be presented. Using multi-nucleon transfer reactions, a wide variety of nuclei around a target nucleus is produced. By identifying transfer channels, fission data of several compound nuclei can be studied in one experiment. Another feature of transfer reaction is that excitation energy of a compound nucleus can be populated widely from the ground state up to several tens MeV, allowing us to study the excitation energy dependence of fission properties. The experiments were carried out in the reactions of O + U, Th, Cm. Results for fission fragment mass distributions and their excitation energy dependence are compared with a model calculation based on a fluctuation dissipation model. Also, experimental data of prompt neutron multiplicity in fission and angular distribution of fission fragments will be discussed.
西尾 勝久; 廣瀬 健太郎; 牧井 宏之; Orlandi, R.; 塚田 和明; Vermeulen, M. J.; Andreyev, A. N.; 千葉 敏; Tsekhanovich, I.*; 大槻 勤*
no journal, ,
We are promoting a campaign to study multi-nucleon transfer reactions to populate excited states in neutron-rich actinide nuclei which cannot be accessed by particle capture and/or fusion reactions. Main purpose of this program is to study fission in new region of chart of nuclei. As a first step we studied reactions using the O beam (
9 MeV/u) and actinide target nuclei such as U, Np, Cm. The experiment was carried out at the tandem facility of Japan Atomic Energy Agency. Ejectile nuclei generated in the reaction were identified by a newly developed silicon E-E detectors. Using this detector, clear separation of oxygen isotopes (
O) was obtained as well as lighter element isotopes (Be, B, C, N). The number of produced nuclei amounted to more than fifteen in one reaction. Two fragments emitted in multi-nucleon transfer fission were detected by multi-wire proportional counters, and the fragment mass distributions were obtained for each isotopes. The measured FFMDs agreed with a calculation based on the fluctuation-dissipation model up to about excitation energy 30 MeV. Measurement of fission fragment angular distribution relative to the recoil direction suggested the increase of the spin with the number of transferred nucleons.
西尾 勝久
no journal, ,
We are promoting a study of fission using multi-nucleon transfer reactions, where excited states in neutron-rich actinide nuclei, which cannot be accessed by particle capture and/or fusion reactions, are populated. This allows us to study fission mechanism in the new region of chart of nuclei. Also, the excited states in the fissioning nucleus are widely populated by the multi-nucleon transfer reactions, from which effects of excitation energy on fission properties can be investigated. Experiments were carried out at the JAEA tandem facility in Tokai, Japan. We studied reactions using the O beam ( 9 MeV/u) and several actinide target nuclei such as Th, U, Np, Cm. Ejectile nuclei were identified by a newly developed silicon E-E detectors (E = 75 
m, E = 300 m). Clear separation of oxygen isotopes (O) was obtained as well as lighter element isotopes (Be, B, C, N). Number of produced nuclei reached to more than fifteen in a single measurement. Both fission fragments were detected by multi-wire proportional counters, and fission fragment mass distributions (FFMDs) were measured for each isotopes. The data allows us to obtain the systematic trends of FFMDs in detail. Measured FFMDs are reproduced by a calculation based on the fluctuation-dissipation model, from which the shell damping energy was determined.
西尾 勝久
no journal, ,
This talk will discuss the use of multi-nucleon transfer (MNT) reactions to study fission properties of multitude exotic nuclei in the neutron-rich actinide region. Most of these nuclei cannot be accessed by the traditional method of complete-fusion reactions. The MNT transfer channels of the O+Th reaction were used to study fission of fourteen nuclei 
Th, 
Pa, and 
U. Fission fragment mass distributions (FFMDs) are measured for each transfer channel. In particular, the FFMDs of 
Th and 
Pa were measured for the first time. Predominantly asymmetric fission is observed at low excitation energies for all studied cases, with a gradual increase of the symmetric mode towards higher excitation energy. By using the same method, the measurements with U, Np, Cm, and 
Cf targets were recently performed. The obtained FFMDs are compared with a calculation based on the fluctuation-dissipation model, where effect of multi-chance fission (neutron evaporation prior to fission) was considered. It was found that multi-chance fission has significant role on the shape of FFMD, particularly at the high-excitation energies.
西尾 勝久
no journal, ,
We are promoting a program of fission studies using multi-nucleon transfer reactions. This approach allows us to investigate fission of neutron-rich nuclei, which cannot be populated by particle capture reactions. From the measurement of fission fragment mass distributions (FFMDs) for various nuclides and their evolution with initial excitation energy, role of multi-chance fission, i.e. neutron emission prior to fission, on FFMD was investigated. The obtained large data set of FFMDs was used to improve the Langevin model to describe low-energy fission, which was applied to the fissions of fermium isotopes. The results explain the origin of the onset of sharp symmetric fission appearing in neutron-rich fermium isotopes. In the presentation, we will also discuss other data obtained in our setup, such as fission barrier height and prompt neutrons in correlation with fission fragments.
西尾 勝久
no journal, ,
Using the JAEA tandem accelerator facility, we are promoting a program to take fission data using multi-nucleon transfer (MNT) reactions. The MNT reaction allows us to produce neutron-rich actinide nuclei, which cannot be populated by particle capture reactions. Fission fragment mass distributions (FFMDs) and fission barrier heights for various nuclei were obtained. The FFMDs and their evolution with initial excitation energies were explained only by invoking a concept of multi-chance fission, i.e. neutron-evaporation before fission.
O+Npの多核子移行反応を用いた核分裂片質量数分布の測定西尾 勝久; Vermeulen, M. J.*; 廣瀬 健太郎; Kean, K. R.*; 牧井 宏之; Orlandi, R.; 塚田 和明; Tsekhanovich, I.*; Andreyev, A. N.; 石崎 翔馬*; et al.
no journal, ,
原子力機構では、多核子移行反応を用いることで多くの複合核核種を生成し、これらの核分裂片質量数分布を測定する手法を開発してきた。本手法は、中性子数の多い核種など、既存の方法では取得が不可能な原子核の核分裂データを取得できる点で画期的である。本発表では、O+Np反応により23核種までのデータを取得した。なお、Np, Pu、およびCmのデータは低エネルギー核分裂データとして最初のデータとなった。
O+Npの多核子移行反応で生成される原子核の核分裂片質量数分布の測定西尾 勝久; Vermeulen, M. J.*; 廣瀬 健太郎; Kean, K. R.*; 牧井 宏之; Orlandi, R.; 塚田 和明; Tsekhanovich, I.*; Andreyev, A. N.; 石崎 翔馬*; et al.
no journal, ,
O+Nの多核子移行反応により23核種の核分裂片質量数分布を取得し、得られた結果を考察した。実験は、原子力機構タンデム加速器(東海)で得られるOビームをNp薄膜標的に照射して行った。多核子移行反応で生成される散乱粒子をシリコンE-E検出器で検出し、イベントごとに核種を同定し、複合核を識別した。この核分裂によって放出される2つの核分裂片を多芯線比例計数管によって検出し、運動学的に核分裂片の質量数を決定した。実験データをランジュバン模型による計算結果と比較した。計算では、(1)反応後の励起エネルギーがすべて複合核に付与されると近似した。また(2)マルチチャンス核分裂、すなわち中性子を放出した後で核分裂が起こる現象を取り入れた。計算結果は、核種と励起エネルギーに対する質量数分布の系統的な変化をよく再現した。一方、系の角運動量が20
を超える条件だと実験データを説明できなかった。移行する陽子の数と中性子の数を変えることで、異なる反応から同じ複合核を生成することができる。一方、系の角運動量が20を超える条件だと実験データを説明できなかった。移行する陽子の数と中性子の数を変えることで、異なる反応から同じ複合核を生成することができる。これまでに行った反応(O+Th, O+U, O+Np)の結果を比べたところ、核分裂片の質量数分布は、多核子移行チャンネルによらずほぼ等しくなることがわかった。
