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論文

Search for $$alpha$$ decay of $$^{104}$$Te with a novel recoil-decay scintillation detector

Xiao, Y.*; Go, S.*; Grzywacz, R.*; Orlandi, R.; Andreyev, A. N.; 浅井 雅人; Bentley, M. A.*; de Angelis, G.*; Gross, C. J.*; Hausladen, P.*; et al.

Physical Review C, 100(3), p.034315_1 - 034315_8, 2019/09

https://doi.org/10.1103/PhysRevC.100.034315
 被引用回数：10 パーセンタイル：88.51(Physics, Nuclear)

A search for super-allowed $$alpha$$ decay of N=Z nuclei $$^{104}$$Te and $$^{108}$$Xe was carried out using a novel recoil-decay scintillator detector at the tandem accelerator facility at Japan Atomic Energy Agency. Inorganic crystal scintillation material of YAP:Ce (Yttrium Aluminium Perovskite) coupled to position-sensitive photo-multiplier tube (PSPMT) was implemented for the first time in a radioactive decay experiment. Residues from the fusion-evaporation reaction $$^{58}$$Ni+$$^{54}$$Fe$$rightarrow$$ $$^{112}$$Xe$$^*$$ were separated by the JAEA Recoil Mass Separator (RMS) and implanted into the YAP:Ce crystal. $$alpha$$ decays of neutron-deficient tellurium isotopes were identified and proton-emission of $$^{109}$$I was observed. No conclusive evidence was found for the decay chain $$^{108}$$Xe$$rightarrow$$$$^{104}$$Te$$rightarrow$$ $$^{100}$$Sn within 3 days experiment. The cross section limit of 130 pb was obtained for production of two events of $$^{108}$$Xe, about an order of magnitude below the expectation based on earlier cross section measurements and HIVAP calculations.

論文

Role of multichance fission in the description of fission-fragment mass distributions at high energies

廣瀬 健太郎; 西尾 勝久; 田中 翔也*; L$'e$guillon, R.*; 牧井 宏之; 西中 一朗*; Orlandi, R.; 塚田 和明; Smallcombe, J.*; Vermeulen, M. J.; et al.

Physical Review Letters, 119(22), p.222501_1 - 222501_6, 2017/12

https://doi.org/10.1103/PhysRevLett.119.222501
 被引用回数：32 パーセンタイル：90.41(Physics, Multidisciplinary)

JAEAタンデム加速器施設で行った$$^{18}$$O+$$^{238}$$U反応における多核子移行チャンネルを用いた実験により、$$^{237-240}$$U, $$^{239-242}$$Np、および$$^{241-244}$$Puの核分裂質量分布を励起エネルギー10$$sim$$60MeVにおいて測定した。これらのうち、$$^{240}$$U, $$^{240,241,242}$$Npのデータは本実験により初めて観測された。原子核の殻効果の減衰によって対称分裂すると予想されていた高励起エネルギーにおいても、質量分布が非対称を示すことがわかった。搖動散逸定理に基づく動力学モデル計算との比較から、この振る舞いはマルチチャンス核分裂によるものであることを明らかにした。

論文

Study of fission using multi-nucleon transfer reactions

西尾 勝久; 廣瀬 健太郎; L$'e$guillon, R.*; 牧井 宏之; Orlandi, R.; 塚田 和明; Smallcombe, J.*; 千葉 敏*; 有友 嘉浩*; 田中 翔也*; et al.

Proceedings of 6th International Conference on Fission and Properties of Neutron-rich Nuclei (ICFN-6), p.590 - 597, 2017/11

https://doi.org/10.1142/9789813229426_0101

We are promoting a fission study 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 in the new region of chart of nuclei. Also, the excited states in the fissioning nucleus are widely populated in the reactions, thus the effects of excitation energy on fission can be investigated. Experiments were carried out at the JAEA tandem facility in Tokai, Japan. We studied reactions using the $$^{18}$$O beam ($$sim$$9MeV/u) and several actinide target nuclei such as $$^{232}$$Th, $$^{238}$$U, $$^{237}$$Np, $$^{248}$$Cm. Ejectile nuclei and thus the transfer channels were identified by a newly developed silicon $$Delta$$E-E detectors. The produced nuclei in one experiment reached more than fifteen. Fission fragment mass distributions (FFMDs) were measured for each isotopes. Measured FFMDs are reproduced by a calculation based on the fluctuation-dissipation model (Langevin-type calculation), where effects of multi-chance fission were included. We also started to measure the prompt neutrons accompanied by fission.

論文

Experimental 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.; 塚田 和明; Smallcombe, J.*; 千葉 敏*; 有友 嘉浩*; 田中 翔也*; et al.

EPJ Web of Conferences, 146, p.04009_1 - 04009_6, 2017/09

https://doi.org/10.1051/epjconf/201714604009
 被引用回数：3 パーセンタイル：92.06

The objective of this work is to extend fission data for actinide nuclei not investigated so far in order to understand the fission mechanism, especially for neutron-rich nuclei. Multi-nucleon transfer reactions were used to populate the compound nuclei which cannot be accessed by particle capture or fusion reactions. The experiment was carried out at the tandem facility of Japan Atomic Energy Agency. In the multi-nucleon transfer reactions using $$^{18}$$O beam, a wide variety of nuclei around a target nucleus was produced. By identifying transfer channels, fission data of nuclei more than fifteen compound nuclei were generated in one experiment. Another feature of transfer reaction is that the excitation energies 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. From the excitation function of fission probabilities, fission-barrier heights of neutron-rich actinide nuclei were obtained. Experiments were carried out in the reactions of $$^{18}$$O + $$^{238}$$U, $$^{232}$$Th, $$^{248}$$Cm, $$^{237}$$Np. The obtained fission fragment mass distributions were reproduced by a model calculation based on a fluctuation dissipation model.

論文

Fission fragments mass distributions of nuclei populated by the multinucleon transfer channels of the $$^{18}$$O + $$^{232}$$Th reaction

L$'e$guillon, R.; 西尾 勝久; 廣瀬 健太郎; 牧井 宏之; 西中 一朗*; Orlandi, R.; 塚田 和明; Smallcombe, J.*; 千葉 敏*; 有友 嘉浩*; et al.

Physics Letters B, 761, p.125 - 130, 2016/10

https://doi.org/10.1016/j.physletb.2016.08.010
 被引用回数：31 パーセンタイル：92.7(Astronomy & Astrophysics)

It is shown that the multinucleon transfer reactions is a powerful tool to study fission of exotic neutron-rich actinide nuclei, which cannot be accessed by particle-capture or heavy-ion fusion reactions. In this work, multinucleon transfer channels of the $$^{18}$$O + $$^{232}$$Th reaction are 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. Identification of fissioning nuclei and of their excitation energy is performed on an event-by-event basis, through the measurement of outgoing ejectile particle in coincidence with fission fragments. Fission fragment mass distributions are measured for each transfer channel, in selected bins of excitation energy. In particular, the mass distributions of $$^{231,234}$$Th and $$^{234,235,236}$$Pa are 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. The experimental distributions are found to be in general agreement with predictions of the fluctuation-dissipation model.

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

Induced fission studies of Z $$<$$ 82 nuclei at the JAEA Tandem Facility

Smallcombe, J.; 西尾 勝久; 廣瀬 健太郎; 西中 一朗; 牧井 宏之; Orlandi, R.; 田村 信行*; 後藤 真一*; 大槻 勤*; Andreyev, A.*; et al.

no journal, , 

Recent $$beta$$-delayed fission studies of proton rich $$^{180}$$Hg showed the fission to be dominated by asymmetric fragment masses, in contrast to initial predictions. Models of the potential-energy surface for the path toward scission showed a lower fission barrier for an asymmetrically deformed $$^{180}$$Hg volume. As a probe of this theoretical interpretation, fission of $$^{180}$$Hg was induced through the symmetric reaction $$^{90}$$Z$$+^{90}$$Z. Mass and energy distributions of fragments for a series of bombarding energies were recorded using 2 MWPCs. As a continuation of Z $$<82$$ fission studies, fission induced in the $$^{7}$$Li$$+^{182,184,186}$$W reactions were measured. Near A$$sim$$190 a new region of asymmetric fission is predicted to emerge as one moves towards neutron rich nuclei. In preliminary investigations mass asymmetry was observed in fragments of the $$^{7}$$Li$$+^{186}$$W reaction. However, fragment kinematics were inconsistent with fission of $$^{193}$$Ir formed by fusion. A follow up experiment was conducted in an attempt to confirm the first observation of fission induced by the $$^{7}$$Li breakup-fusion reaction $$^{186}$$W$$(^{7}$$Li,$$^{4}$$He$$)^{189}$$Re. Experimental details and initial results will be presented.

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

$$^{235}$$U熱中性子核分裂における即発$$gamma$$線スペクトルの測定

牧井 宏之; 西尾 勝久; 西中 一朗; 廣瀬 健太郎; Orlandi, R.; Smallcombe, J.; L$'e$guillon, R.; 関本 俊*; 高宮 幸一*; 大槻 勤*

no journal, , 

福島第一原子力発電所では廃止措置に向け、溶解しデブリとなった核燃料の取り出しが計画されている。その際、体系が未臨界であることを保証しながら作業を進める必要があるが、そのためには核分裂事象の頻度を観測する必要がある。しかしながら、使用済核燃料から放出されるバックグラウンド$$gamma$$線等により、核分裂事象に伴い発生する即発中性子を観測することは容易ではない。一方、$$^{252}$$Cfの自発核分裂事象においては、核分裂生成物の$$beta$$崩壊等で生じる$$gamma$$線(最大数MeV)を超える高エネルギー$$gamma$$線が発生することが知られている。我々はこの高エネルギー$$gamma$$線に感度を有する未臨界監視$$gamma$$線検出器の開発を提案している。しかしながら、$$^{235}$$Uの熱核分裂事象においては最大7MeVまでの$$gamma$$線しか測定されていない。そこで我々は未臨界監視$$gamma$$線検出器の開発に資するため、$$^{235}$$Uの熱核分裂事象において発生する、最大20MeVまでの高エネルギー$$gamma$$線の収率を確認することを目的とした測定を開始した。本発表ではバックグラウンド$$gamma$$の発生量等を確認した試験測定の結果を報告する。

口頭

新たな未臨界監視検出器をめざした核分裂高エネルギー$$gamma$$線の測定

西尾 勝久; 牧井 宏之; 廣瀬 健太郎; 西中 一朗; Orlandi, R.; Smallcombe, J.; 大槻 勤*; 関本 俊*; 高宮 幸一*

no journal, , 

福島第一原子力発電所の廃止措置において燃料デブリを取り出す際、臨界監視を行って安全を確保する必要がある。これは、体系内での核分裂事象の頻度を検出することで決定するが、環境からの強いバックグランド$$gamma$$線下で事象を検出する必要がある。ここでは、核分裂に伴って放出される高エネルギーの即発$$gamma$$線(6MeV以上)を測定する方法を提案する。本研究は、このための基礎データとなる$$^{235}$$U(n$$_{th}$$,f)の$$gamma$$線スペクトルを高エネルギー領域まで測定することを目的とする。発表では、開発した$$gamma$$線検出器のテスト実験について報告する。

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

Fission study by multi-nucleon transfer reaction at JAEA

廣瀬 健太郎; 西尾 勝久; L$'e$guillon, R.; 牧井 宏之; 西中 一朗; Orlandi, R.; Smallcombe, J.; 石井 哲朗; 塚田 和明; 浅井 雅人; et al.

no journal, , 

We have developed a measurement system for the multi-nucleon transfer reaction and been studying fission of short-lived minor actinides and neutron-rich nuclides. The experiment was performed at the tandem accelerator facility of Japan Atomic Energy Agency where targets of $$^{238}$$U, $$^{232}$$Th, $$^{248}$$Cm were irradiated with $$^{18}$$O beams. In this experiment, more than ten nuclides were excited up to few tens of MeV at a time. Projectile-like scattered particles after the multi-nucleon transfer reaction were detected and identified using a $$Delta$$E-E silicon telescope. The mass distribution was deduced from the time difference between two fission fragments from the compound nucleus which were detected using two pairs of multi-wire proportional counters. Neutrons accompanied by fission were also measured using liquid scintillators placed around the reaction chamber. In the nucleon transfer reaction, the axis of the angular-momentum transfer can be determined from the direction of the scattered particle. This is one of the most different point from the neutron/ion-induced fusion-fission reaction where only the plane on which the axis lies can be determined. The fission angular distributions with respect to this axis as well as the mass yield, the prompt neutron multiplicity and so on will be presented.

口頭

$$^{18}$$O+$$^{248}$$Cm反応における核子移行核分裂の測定

廣瀬 健太郎; 西尾 勝久; L$'e$guillon, R.; Smallcombe, J.; 西中 一朗; 牧井 宏之; Orlandi, R.; 塚田 和明; 千葉 敏*; 大槻 勤*; et al.

no journal, , 

短寿命アクチノイド核種や中性子過剰アクチノイド核種の核分裂を研究するために、我々は多核子移行反応測定システムを構築し、$$^{18}$$O+$$^{238}$$U, $$^{18}$$O+$$^{232}$$Th反応における多核子移行核分裂の測定を行ってきた。今回は$$^{18}$$O+$$^{248}$$Cm反応の測定を行い、$$^{247-250}$$Cm, $$^{249-252}$$Bk, $$^{251-254}$$Cfの核分裂質量分布を得た。実験は原子力研究開発機構のタンデム加速器施設で行った。エネルギー162MeVに加速した$$^{18}$$Oビームを、ニッケル箔に電着した$$^{248}$$Cm標的に照射することでさまざまな複合核を合成した。核子を移行した後の散乱粒子を、シリコン検出器を使って同定することで、複合核の核種を知ることができる。2つの核分裂片を多芯線比例計数検出器を使って、散乱粒子と同時計測することで、合成した複合核の核分裂を観測した。$$^{249}$$Cm, $$^{249-251}$$Bk, $$^{251,253}$$Cfの核分裂質量分布は本測定により初めて得られた。

口頭

Study for fission using multi-nucleon transfer reaction

西尾 勝久; 廣瀬 健太郎; L$'e$guillon, R.; 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

Surrogate reactions for neutron-induced fission reaction and capture reaction by heavy ion transfer reactions

牧井 宏之; 西尾 勝久; 廣瀬 健太郎; Orlandi, R.; Yan, S. Q.*; L$'e$guillon, R.; Smallcombe, J.*; Vermeulen, M. J.; 西中 一朗*; 塚田 和明; et al.

no journal, , 

原子力機構タンデム加速器施設で進行中の、中性子反応核データを間接的に導出する代理反応の研究について紹介する。我々は重イオン核子移行反応で生成された複合核を同定するためのシリコン$$Delta$$E-E検出器、核分裂片を検出するための多芯線比例計数管(MWPC)、複合核からの$$gamma$$線を観測するためのコンプトン抑止型LaBr$$_{3}$$(Ce)シンチレータ、及び核分裂即発中性子を検出するための液体シンチレータから構成された測定装置の開発を行ってきた。得られた結果のうち、代理反応法で導出した核分裂断面積, 中性子捕獲断面積について議論する。

口頭

Fission yield measurement using multi-nucleon transfer reactions

廣瀬 健太郎; 西尾 勝久; 田中 翔也*; Leguillon, R.*; 牧井 宏之; 西中 一朗*; Orlandi, R.; 塚田 和明; Smallcombe, J.*; Vermeulen, M. J.*; et al.

no journal, , 

The multi-nucleon transfer reaction is very useful way to populate a multitude of nuclides in a wide excitation energy range. We have developed a measurement system at the JAEA tandem accelerator facility to obtain fission observables such as fission-fragment mass distributions (FFMD), prompt fission neutron multiplicities and so on. By identifying the ejectile, the initial compound nucleus is also identified. At high excitation energies, fission of nuclides produced via neutron emission from the initial compound nucleus also contribute to FFMD. In the present study, effects of the multi-chance fission on FFMDs were successfully separated by a combination of a systematic data set obtained from experiments using $$^{18}$$O beams and actinide targets and a dynamical fission calculation based on the fluctuation-dissipation model.

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