検索対象:     
報告書番号:
※ 半角英数字
 年 ~ 
 年
検索結果: 14 件中 1件目~14件目を表示
  • 1

発表形式

Initialising ...

選択項目を絞り込む

掲載資料名

Initialising ...

発表会議名

Initialising ...

筆頭著者名

Initialising ...

キーワード

Initialising ...

使用言語

Initialising ...

発行年

Initialising ...

開催年

Initialising ...

選択した検索結果をダウンロード

論文

核データ研究の最前線; たゆまざる真値の追及、そして新たなニーズへ応える為に,3; 核分裂データの最前線; 実験と理論

西尾 勝久; 千葉 敏*

日本原子力学会誌, 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。

論文

Four-dimensional Langevin approach to low-energy nuclear fission of $$^{236}$$U

石塚 知香子*; Usang, M. D.*; Ivanyuk, F. A.*; Maruhn, J. A.*; 西尾 勝久; 千葉 敏

Physical Review C, 96(6), p.064616_1 - 064616_9, 2017/12

 被引用回数:11 パーセンタイル:8.11(Physics, Nuclear)

We developed a four-dimensional (4D) Langevin model, which can treat the deformation of each fragment independently and applied it to low-energy fission of $$^{236}$$U, the compound system of the reaction n + $$^{235}$$U. The potential energy is calculated with the deformed two-center Woods-Saxon (TCWS) and the Nilsson-type potential with the microscopic energy corrections following the Strutinsky method and BCS pairing. The transport coefficients are calculated by macroscopic prescriptions. It turned out that the deformation for the light and heavy fragments behaves differently, showing a sawtooth structure similar to that of the neutron multiplicities of the individual fragments $$nu$$(A). Furthermore, the measured total kinetic energy TKE(A) and its standard deviation are reproduced fairly well by the 4D Langevin model based on the TCWS potential in addition to the fission fragment mass distributions. The developed model allows a multi-parametric correlation analysis among, e.g., the three key fission observables, mass, TKE, and neutron multiplicity, which should be essential to elucidate several longstanding open problems in fission such as the sharing of the excitation energy between the fragments.

論文

Study of fission using multi-nucleon transfer reactions

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 (Internet), 163, p.00041_1 - 00041_6, 2017/11

 パーセンタイル:100

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 $$^{18}$$O beam and several actinide target nuclei such as $$^{232}$$Th, $$^{238}$$U, $$^{237}$$Np, $$^{248}$$Cm. Ejectile nucleus was identified by a silicon $$Delta$$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.

論文

Excitation energy dependence of fragment-mass distributions from fission of $$^{180,190}$$Hg formed in fusion reactions of $$^{36}$$Ar + $$^{144,154}$$Sm

西尾 勝久; Andreyev, A. N.*; Chapman, R.*; Derkx, X.*; D$"u$llmann, C. E.*; Ghys, L.*; He${ss}$berger, F. P.*; 廣瀬 健太郎; 池添 博*; Khuyagbaatar, J.*; et al.

Physics Letters B, 748, p.89 - 94, 2015/09

 被引用回数:9 パーセンタイル:26.51(Astronomy & Astrophysics)

Mass distributions of fission fragments from the compound nuclei $$^{180}$$Hg and $$^{190}$$Hg formed in fusion reactions $$^{36}$$Ar+$$^{144}$$Sm and $$^{36}$$Ar+$$^{154}$$Sm, respectively, were measured at initial excitation energies of $$E^*$$($$^{180}$$Hg)=,33$$-$$66 MeV and $$E^*$$($$^{190}$$Hg)=,48$$-$$71 MeV. In the fission of $$^{180}$$Hg, the mass spectra were well reproduced by assuming only an asymmetric-mass division, with most probable light and heavy fragment masses $$bar{A}_{rm L}$$/$$bar{A}_{rm H}=$$79$$/$$101. The mass asymmetry for $$^{180}$$Hg agrees well with that obtained in the low-energy $$beta^textrm{+}$$/EC-delayed fission of $$^{180}$$Tl, from our earlier ISOLDE(CERN) experiment. Fission of $$^{190}$$Hg is found to proceed in a similar way, delivering the mass asymmetry of $$bar{A}_{rm L}$$/$$bar{A}_{rm H}=$$83$$/$$107, throughout the measured excitation energy range. The persistence as a function of excitation energy of the mass-asymmetric fission for both proton-rich Hg isotopes gives strong evidence for the survival of microscopic effects up to effective excitation energies of compound nuclei as high as 40,MeV. This behavior is different from fission of actinide nuclei and heavier mercury isotope $$^{198}$$Hg.

論文

Fragment mass distribution of the $$^{239}$$Pu(${it d,pf}$) reaction via the superdeformed $$beta$$-vibrational resonance

西尾 勝久; 池添 博; 永目 諭一郎; 光岡 真一; 西中 一朗; Duan, L.*; 佐藤 健一郎; 後藤 真一*; 浅井 雅人; 羽場 宏光; et al.

Physical Review C, 67(1), p.014604_1 - 014604_5, 2003/01

 被引用回数:8 パーセンタイル:46.1(Physics, Nuclear)

核分裂の双山障壁の第二の谷には、$$beta$$-振動準位が存在する。本研究は、この振動準位を経由したときの核分裂片質量数分布を初めて測定したものである。かつて、障壁上にある$$gamma$$振動準位を経由したとされる核分裂実験が行われたことがあり、その結果は質量非対称成分が増加したと報告されている。$$beta$$振動準位を経由すれば、対称分裂が支配的になると考えた。$$beta$$振動レベルに励起状態が一致すると、共鳴トンネル核分裂によって核分裂断面積が増大するので、この共鳴ピークにゲートをかけて質量数分布を測定した。得られた結果は、($$^{240}$$Puの核分裂),Pu-239熱中性子核分裂や、$$^{240}$$Pu isomerと同じような質量非対称な分布であった。$$beta$$振動準位を経由しても、系は従来の質量非対称ポテンシャルの谷をころがり落ちること、つまり質量対称のポテンシャルの谷には現れないことがわかった。

口頭

$$^{7}$$Li+$$^{186}$$W反応で観測された質量非対称核分裂

田村 信行; 廣瀬 健太郎; 西尾 勝久; 西中 一朗; 牧井 宏之; Orlandi, R.; L$'e$guillon, R.; Smallcombe, J.; Andreyev, A.; 大槻 勤*; et al.

no journal, , 

原子力機構・先端基礎研究センターでは、陽子過剰核$$^{180}$$Hgにおいて質量非対称な核分裂を観測し、アクチノイド原子核以外にも質量非対称分布を示す新たな領域が独立して存在することを明らかにした。理論によれば、鉛より軽い元素の中性子過剰核側に新たな質量非対称核分裂を示す原子核が存在するとされた。これを確認することを目的とし、本実験研究では、$$^{7}$$Li+$$^{186}$$W反応で生成される原子核の質量数分布を測定した。比較実験のため、$$^{7}$$Li+$$^{182,184}$$W反応も調べた。実験は、原子力機構タンデム加速器施設で行った。この結果、$$^{7}$$Li+$$^{186}$$W反応において質量非対称分裂を観測した。解析の結果、$$^{7}$$Liのブレークアップによって生成された$$^{3}$$Hが$$^{186}$$Wに吸収されてできる$$^{189}$$Reが質量非対称分裂の原因であると考えられた。

口頭

Study for fission using multi-nucleon transfer reaction

西尾 勝久; 廣瀬 健太郎; L$'e$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 $$^{18}$$O + $$^{238}$$U and $$^{18}$$O + $$^{232}$$Th. Transfer channel and the excitation energy of compound nucleus were determined by using silicon $$Delta$$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.

口頭

Fission study of actinide nuclei using multi-nucleon transfer reaction

西尾 勝久; 廣瀬 健太郎; L$'e$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, , 

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 $$^{18}$$O + $$^{238}$$U and $$^{18}$$O + $$^{232}$$Th. Transfer channel and the excitation energy of the compound nucleus were determined by using silicon $$Delta$$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.

口頭

Fission study using multi-nucleon transfer reactions

西尾 勝久; 廣瀬 健太郎; L$'e$guillon, R.; 牧井 宏之; Orlandi, R.; 西中 一朗; Smallcombe, J.; 千葉 敏*; 荒木 祥平*; 渡辺 幸信*; et al.

no journal, , 

A recent development for fission study using multi-nucleon transfer reactions at the JAEA tandem facility will be presented. Using multi-nucleon transfer reactions, a wide variety of nuclei including neutron-rich nuclei around a target nucleus is produced. By identifying a 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 continuously 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 $$^{18}$$O + $$^{238}$$U,$$^{232}$$Th,$$^{248}$$Cm. Results for fission fragment mass distributions and their excitation energy dependence are compared with a 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.

口頭

Study for fission using multi-nucleon transfer reaction

西尾 勝久; 廣瀬 健太郎; L$'e$guillon, 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 $$^{18}$$O + $$^{238}$$U, $$^{232}$$Th, $$^{248}$$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.

口頭

Experimental study of fission using multinucleon transfer reactions

西尾 勝久; 廣瀬 健太郎; 牧井 宏之; Orlandi, R.; 塚田 和明; Vermeulen, M. J.; Andreyev, A.; 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 $$^{18}$$O beam ($$sim$$ 9 MeV/u) and actinide target nuclei such as $$^{238}$$U, $$^{237}$$Np, $$^{248}$$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 $$Delta$$E-E detectors. Using this detector, clear separation of oxygen isotopes ($$^{16,17,18,19}$$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.

口頭

Study of fission using multi-nucleon transfer reactions

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 $$^{18}$$O beam ($$sim$$ 9 MeV/u) and several actinide target nuclei such as $$^{232}$$Th, $$^{238}$$U, $$^{237}$$Np, $$^{248}$$Cm. Ejectile nuclei were identified by a newly developed silicon $$Delta$$E-E detectors ($$Delta$$E = 75 $$mu$$m, E = 300 $$mu$$m). Clear separation of oxygen isotopes ($$^{16,17,18,19}$$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.

口頭

Fission study using multi-nucleon transfer reaction at JAEA tandem

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 $$^{18}$$O+$$^{232}$$Th reaction were used to study fission of fourteen nuclei $$^{231,232,233,234}$$Th, $$^{232,233,234,235,236}$$Pa, and $$^{234,235,236,237,238}$$U. Fission fragment mass distributions (FFMDs) are measured for each transfer channel. In particular, the FFMDs of $$^{234}$$Th and $$^{234,235,236}$$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 $$^{238}$$U, $$^{237}$$Np, $$^{248}$$Cm, and $$^{249}$$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.

口頭

Fission studies using multi-nucleon transfer reactions

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.

14 件中 1件目~14件目を表示
  • 1