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論文

Observation of the competing fission modes in $$^{178}$$Pt

Tsekhanovich, I.*; Andreyev, A.; 西尾 勝久; Denis-Petit, D.*; 廣瀬 健太郎; 牧井 宏之; Matheson, Z.*; 森本 幸司*; 森田 浩介*; Nazarewicz, W.*; et al.

Physics Letters B, 790, p.583 - 588, 2019/03

http://dx.doi.org/10.1016/j.physletb.2019.02.006
 被引用回数：2 パーセンタイル：14.11(Astronomy & Astrophysics)

Fragment mass distributions from fission of the excited compound nucleus $$^{178}$$Pt have been deduced from the measured fragment velocities. The $$^{178}$$Pt nucleus was created at the JAEA tandem facility in a complete fusion reaction $$^{36}$$Ar+$$^{142}$$Nd, at beam energies of 155, 170 and 180 MeV. The data are indicative of a mixture of the mass-asymmetric and mass-symmetric fission modes associated with higher and lower total kinetic energies of the fragments, respectively. The measured fragment yields are dominated by asymmetric mass splits, with the symmetric mode contributing at the level of $$approx$$ 1/3. This constitutes the first observation of a multimodal fission in the sub-lead region. Most probable experimental fragment-mass split of the asymmetric mode, $$A_{rm L}$$/$$A_{rm H}$$ $$approx$$ 79/99, is well reproduced by nuclear density functional theory using the UNEDF1-HFB and D1S potentials. The symmetric mode is associated by theory with very elongated fission fragments, which is consistent with the observed total kinetic energy/fragment mass correlation.

論文

First ionization potentials of Fm, Md, No, and Lr; Verification of filling-up of 5f electrons and confirmation of the actinide series

佐藤 哲也; 浅井 雅人; Borschevsky, A.*; Beerwerth, R.*; 金谷 佑亮*; 牧井 宏之; 水飼 秋菜*; 永目 諭一郎; 長 明彦; 豊嶋 厚史; et al.

Journal of the American Chemical Society, 140(44), p.14609 - 14613, 2018/11

http://dx.doi.org/10.1021/jacs.8b09068
 被引用回数：4 パーセンタイル：21.13(Chemistry, Multidisciplinary)

第一イオン化エネルギー(IP$$_1$$)は、原子の価電子軌道に関する情報を与える。99番元素アインスタイニウムよりも重いアクチノイドのIP$$_1$$は、一度に一つの原子しか扱うことのできない実験の難しさから、これまでに実験的に測定された例はなかった。我々は表面電離法を応用した新しい測定手法により、103番元素ローレンシウム(Lr)のIP$$_1$$測定に成功し、Lrが弱く束縛された最外殻電子をもつことを強く示唆する結果を得た。一方、Lrとは対象的に、102番元素ノーベリウムは充填された5f軌道および7s軌道をもつために、アクチノイド中最高のIP$$_1$$をもつと考えられている。表面電離法によるIP$$_1$$決定法をNoおよび100番元素フェルミウム, 101番元素メンデレビウムに適用することにより求められた各IP$$_1$$から、5f軌道への電子の充填に伴ってIP$$_1$$が単調に増加し、Noで最も大きくなることを確かめることができた。このことから、f軌道に電子が充填され、アクチノイド系列がLrで終わることを実験的に確かめた。

論文

A New detector system for the measurement of high-energy prompt $$gamma$$-rays for low-energy neutron induced fission

牧井 宏之; 西尾 勝久; 廣瀬 健太郎; Orlandi, R.; L$'e$guillon, R.*; 小川 達彦; Soldner, T.*; Hambsch, F.-J.*; A$"i$che, M.*; Astier, A.*; et al.

Nuclear Instruments and Methods in Physics Research A, 906, p.88 - 96, 2018/10

http://dx.doi.org/10.1016/j.nima.2018.07.055
 パーセンタイル：100(Instruments & Instrumentation)

中性子誘起核分裂における即発高エネルギー$$gamma$$線を観測するための新しい測定システムの開発を行った。測定システムは核分裂片を観測するための多芯線比例計数管と$$gamma$$線測定用のLaBr$$_{3}$$(Ce)シンチレータから構成される。開発したシステムを仏国ラウエ・ランジュバン研究所にある高中性子束炉のPF1Bコースに設置して、$$^{235}$$U中性子誘起核分裂における即発$$gamma$$線を行った。測定ではエネルギー最大20MeVまでの$$gamma$$線スペクトルの観測に成功し、$$^{235}$$U中性子誘起核分裂において非常に高いエネルギーの$$gamma$$線が放出されていることを確認した。

論文

Production of iodine radionuclides using $$^{7}$$Li ion beams

西中 一朗*; 横山 明彦*; 鷲山 幸信*; 牧井 宏之; 橋本 和幸*

Journal of Radioanalytical and Nuclear Chemistry, 314(3), p.1947 - 1965, 2017/12

http://dx.doi.org/10.1007/s10967-017-5525-2
 被引用回数：1 パーセンタイル：64.68(Chemistry, Analytical)

$$^{7}$$Li + $$^{nat}$$Sn反応により生成されるI, Te, Sn同位体の生成断面積を入射エネルギー24-59MeVの領域で測定した。得られた生成断面積のエネルギー依存性を統計模型計算の結果と比較することにより、各同位体の生成機構と崩壊様式の観点から完全・不完全融合反応の生成断面積への寄与を議論した。また、医学的に有用な$$^{123,124}$$Iの生成という観点から、様々なSn同位体と$$^{7}$$Liビームの組み合わせにより、$$^{123,124,125,126}$$I同位体がどの程度生成されるかを計算し、$$^{7}$$Li以外をビームとして用いた場合との比較を行った。

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

http://dx.doi.org/10.1103/PhysRevLett.119.222501
 被引用回数：12 パーセンタイル：11.2(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; 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

http://dx.doi.org/10.1051/epjconf/201716300041
 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

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

The $$^{95}$$Zr($$n, gamma$$)$$^{96}$$Zr cross section from the surrogate ratio method and its effect on $$s$$-process nucleosynthesis

Yan, S. Q.*; Li, Z. H.*; Wang, Y. B.*; 西尾 勝久; Lugaro, M.*; Karakas, A. I.*; 牧井 宏之; Mohr, P.*; Su, J.*; Li, Y. J.*; et al.

Astrophysical Journal, 848(2), p.98_1 - 98_8, 2017/10

http://dx.doi.org/10.3847/1538-4357/aa8c74
 パーセンタイル：100(Astronomy & Astrophysics)

The $$^{95}$$Zr($$n, gamma$$)$$^{96}$$Zr reaction cross section is crucial in the modelling of $$s$$-process nucleosynthesis in asymptotic giant branch stars because it controls the operation of the branching point at the unstable $$^{95}$$Zr and the subsequent production of $$^{96}$$Zr. We have carried out the measurement of the $$^{90}$$Zr($$^{18}$$O,$$^{16}$$O) and $$^{94}$$Zr($$^{18}$$O,$$^{16}$$O) reactions and obtained the $$gamma$$-decay probability ratio of $$^{92}$$Zr$$^{*}$$ and $$^{96}$$Zr$$^{*}$$ to determine the $$^{95}$$Zr($$n, gamma$$)$$^{96}$$Zr reaction cross sections with the surrogate ratio method. We tested our deduced maxwellian-averaged cross section in stellar models with masses between 2 and 6 $$M_{odot}$$ and metallicities 0.014 and 0.03. The largest changes - up 80 % variations in $$^{96}$$Zr - are seen in the models of 3-4 $$M_{odot}$$, where the $$^{22}$$Ne neutron source is mildly activated. The new rate can still provide a match to data from meteoritic stardust silicon carbide grains, provided the maximum mass of the parent stars is below 4 $$M_{odot}$$, for a metallicity of 0.03.

論文

Measurement of high-energy prompt $$gamma$$-rays from neutron induced fission of U-235

牧井 宏之; 西尾 勝久; 廣瀬 健太郎; Orlandi, R.; L$'e$guillon, R.; 小川 達彦; Soldner, T.*; Hambsch, F.-J.*; Astier, A.*; Pollitt, A.*; et al.

EPJ Web of Conferences (Internet), 146, p.04036_1 - 04036_4, 2017/09

http://dx.doi.org/10.1051/epjconf/201714604036
 被引用回数：2 パーセンタイル：4.05

核分裂に伴い放出される即発$$gamma$$線スペクトルの測定は高励起状態にある中性子過剰な核分裂片の脱励起過程を理解する上で重要であると同時に、革新的原子炉の設計といった応用分野においても重要である。これまで$$^{252}$$Cfの自発核分裂においては、核分裂片の巨大共鳴振動が励起されていることを示唆する、8MeVから20MeVにおいて膨らみを持つ高エネルギー$$gamma$$線が観測されていることが知られている。巨大共鳴振動励起の起源を理解するためには$$^{252}$$Cfの自発核分裂以外で即発$$gamma$$線スペクトルを測定する必要があるが、中性子誘起核分裂においては最近の測定においても9MeV程度までしか観測されていない。我々は$$^{235}$$U(n,f)においても20MeVまでの即発$$gamma$$線スペクトルの観測を目的とした測定を仏国ラウエ・ランジュバン研究所にある高中性子束炉の大強度冷中性子ビームを用いて行った。発表では測定で得られた結果について報告する。

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 (Internet), 146, p.04009_1 - 04009_6, 2017/09

http://dx.doi.org/10.1051/epjconf/201714604009
 被引用回数：2 パーセンタイル：4.05

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

Simultaneous measurement of neutron-induced fission and capture cross sections for $$^{241}$$Am at neutron energies below fission threshold

廣瀬 健太郎; 西尾 勝久; 牧井 宏之; 西中 一朗*; 太田 周也*; 永山 達郎*; 田村 信行*; 後藤 真一*; Andreyev, A.; Vermeulen, M. J.; et al.

Nuclear Instruments and Methods in Physics Research A, 856, p.133 - 138, 2017/06

http://dx.doi.org/10.1016/j.nima.2016.12.021
 被引用回数：3 パーセンタイル：27.27(Instruments & Instrumentation)

Fission and capture reactions were simultaneously measured in the neutron-induced reactions of $$^{241}$$Am at J-PARC. Data were taken with the TOF method in $$E_n$$ = 0.1$$sim$$20 eV. The fission events were observed by detecting prompt fission neutrons using liquid organic scintillators. The capture reaction was measured by detecting $$gamma$$ rays from the compound nuclei using the same detectors, where the prompt fission neutrons and capture $$gamma$$ rays were separated by a pulse shape analysis. The cross sections were obtained by normalizing the relative yields at the first resonance to evaluations or other experimental data. The ratio of the fission to capture cross sections at each resonance is compared with those from an evaluated nuclear data library and other experimental data. Some differences were found between the present values and the library/literature values at several resonances.

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

http://dx.doi.org/10.1016/j.physletb.2016.08.010
 被引用回数：18 パーセンタイル：7.21(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.

論文

Examination of the surrogate ratio method for the determination of the $$^{93}$$Zr(n,$$gamma$$)$$^{94}$$Zr cross section with $$^{90,92}$$Zr($$^{18}$$O,$$^{16}$$O)$$^{92,94}$$Zr reactions

Yan, S. Q.*; Li, Z. H.*; Wang, Y. B.*; 西尾 勝久; 牧井 宏之; Su, J.*; Li, Y. J.*; 西中 一朗; 廣瀬 健太郎; Han, Y. L.*; et al.

Physical Review C, 94(1), p.015804_1 - 015804_5, 2016/07

http://dx.doi.org/10.1103/PhysRevC.94.015804
 被引用回数：3 パーセンタイル：52.92(Physics, Nuclear)

The relative $$gamma$$-decay probability ratios of the neutron resonance states in $$^{94}$$Zr and $$^{92}$$Zr populated via two neutron transfer reactions, $$^{92}$$Zr($$^{18}$$O,$$^{16}$$O)$$^{94}$$Zr and $$^{90}$$Zr($$^{18}$$O,$$^{16}$$O)$$^{92}$$Zr, have been measured to test the validity of the surrogate ratio method (SRM) in determining the (n,$$gamma$$) reaction cross section. The cross sections of the $$^{93}$$Zr(n,$$gamma$$)$$^{94}$$Zr reaction are derived from the experimentally obtained ratios and the cross sections of the $$^{91}$$Zr(n,$$gamma$$)$$^{92}$$Zr reaction in the equivalent neutron energy range of $$E_{rm n}$$ = 0 - 8 MeV. The deduced cross sections of $$^{93}$$Zr(n,$$gamma$$)$$^{94}$$Zr reaction agree with the directly measured ones in the low-energy region, and with the evaluated ENDF/B-VII.1 data at higher energies of $$E_{rm n} >$$ 3 MeV. The agreement supports the concept of the SRM method to indirectly determine the (n,$$gamma$$) reaction cross sections.

論文

Direct measurement of nanoscale lithium diffusion in solid battery materials using radioactive tracer of $$^{8}$$Li

石山 博恒*; Jeong, S.-C.*; 渡辺 裕*; 平山 賀一*; 今井 伸明*; Jung, H. S.*; 宮武 宇也*; 小柳津 充広*; 長 明彦; 乙川 義憲; et al.

Nuclear Instruments and Methods in Physics Research B, 376, p.379 - 381, 2016/06

http://dx.doi.org/10.1016/j.nimb.2015.12.036
 被引用回数：2 パーセンタイル：57.25(Instruments & Instrumentation)

We have developed an in situ and nanoscale Li diffusion measurement method in Li battery materials using an $$alpha$$-emitting radioactive $$^{8}$$Li tracer. In this method, while implanting a low-energy (8 keV) $$^{8}$$Li beam, the $$alpha$$ particles emitted at a small angle (10$$^{circ}$$) relative to the sample surface were detected as a function of time. Measurement for Li diffusion coefficients in a spinel phase LiMn$$_4$$O$$_4$$ (LMO) thin film has been started, which is used as an electrode in a Li ion secondary battery. An obvious Li diffusion effect in LMO was observed at the sample temperature of 623 K, and the further measurement is underway.

論文

A Comprehensive approach to determination of nuclear data of unstable nuclei

千葉 敏*; 西尾 勝久; 有友 嘉浩*; 小浦 寛之; 岩本 修; 牧井 宏之; 西中 一朗*; 廣瀬 健太郎

EPJ Web of Conferences (Internet), 106, p.04004_1 - 04004_9, 2016/02

http://dx.doi.org/10.1051/epjconf/201610604004
 パーセンタイル：100

A comprehensive approach to determine nuclear data of unstable nuclei will be described. It consists of a measurement of fission and capture cross sections, mass distribution of fission fragments (independent fission yields) and number of prompt fission neutrons by the method of surrogate reactions. A multi-dimensional Langevin model is being developed to estimate the independent fission yields theoretically. Furthermore, the $$beta$$ decay properties of the fission fragments, almost all are neutron-rich unstable nuclei, are investigated systematically by improving the gross theory of $$beta$$ decay, which will yield information on the decay heat and delayed-neutron data.

論文

Development of a measurement system for the determination of ($$n,gamma$$) cross-sections using multi-nucleon transfer reactions

牧井 宏之; 太田 周也*; 石井 哲朗; 若林 泰生*; 古高 和禎; 西尾 勝久; 西中 一朗; 千葉 敏; 井頭 政之*; Czeszumska, A.*

Nuclear Instruments and Methods in Physics Research A, 797, p.83 - 93, 2015/10

http://dx.doi.org/10.1016/j.nima.2015.05.005
 被引用回数：3 パーセンタイル：53.75(Instruments & Instrumentation)

中性子捕獲断面積を間接的に導出するための、$$gamma$$線測定用のコンプトン抑止型LaBr$$_{3}$$(Ce)検出器と荷電粒子測定用のシリコン$${Delta}E$$-$$E$$検出器から構成される、新しい測定装置の開発を行った。原子力機構タンデム加速器からのエネルギー153MeVの酸素18ビームを$$^{155}$$Gd及び、$$^{157}$$Gd標的に照射して発生する$$gamma$$線と荷電粒子の同時測定を行うことにより、開発した装置の特性試験を行った。大型(直径4インチ、長さ5インチ)のLaBr$$_{3}$$(Ce)検出器を用いることにより、$$^{155}$$Gd($$^{18}$$O, $$^{16}$$O)$$^{157}$$Gd反応及び、$$^{157}$$Gd($$^{18}$$O, $$^{16}$$O)$$^{159}$$Gd反応で生成される複合核からの$$gamma$$線の測定に成功した。得られた結果から新たに開発した測定装置が多核子移行反応を用いた中性子捕獲断面積の導出に極めて有効であることを見出した。

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

http://dx.doi.org/10.1016/j.physletb.2015.06.068
 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

Production and separation of astatine isotopes in the $$^7$$Li + $$^{nat}$$Pb reaction

西中 一朗; 横山 明彦*; 鷲山 幸信*; 前田 英太*; 渡辺 茂樹; 橋本 和幸; 石岡 典子; 牧井 宏之; 豊嶋 厚史; 山田 記大*; et al.

Journal of Radioanalytical and Nuclear Chemistry, 304(3), p.1077 - 1083, 2015/06

http://dx.doi.org/10.1007/s10967-015-3975-y
 被引用回数：3 パーセンタイル：53.75(Chemistry, Analytical)

29-57MeVの$$^7$$Liビームと$$^{nat}$$Pb標的核の反応においてアスタチン同位体$$^{207-211}$$Atの生成断面積を$$alpha$$線, $$gamma$$線スペクトルメトリーで測定した。生成断面積の励起関数を統計模型モデル計算と比較することで、$$^7$$Li + $$^{nat}$$Pbの反応機構を調べた。44MeVより大きい入射エネルギーでの$$^{210}$$Atと$$^{209}$$Atの生成断面積が理論値よりも小さいことから、分解反応が存在することを明らかにした。照射した鉛標的からのアスタチンの化学分離を乾式蒸留法に基づいて調べ、アスタチン製造の相補的な手法を開発した。

論文

Nanoscale diffusion tracing by radioactive $$^{8}$$Li tracer

石山 博恒*; Jeong, S.-C.*; 渡辺 裕*; 平山 賀一*; 今井 伸明*; 宮武 宇也*; 小柳津 充広*; 片山 一郎*; 長 明彦; 乙川 義憲; et al.

Japanese Journal of Applied Physics, 53(11), p.110303_1 - 110303_4, 2014/11

http://dx.doi.org/10.7567/JJAP.53.110303
 被引用回数：3 パーセンタイル：78.29(Physics, Applied)

We have developed a nanoscale diffusion measurement method using an $$alpha$$-emitting radioactive $$^{8}$$Li tracer. In this method, while implanting a pulsed 8 keV $$^{8}$$Li beam, the $$alpha$$ particles emitted at a small angle (10$$^{circ}$$) relative to the sample surface were detected as a function of time. The method has been successfully applied to measuring lithium diffusion coefficients for an amorphous Li$$_{4}$$SiO$$_{4}$$-Li$$_{3}$$VO$$_{4}$$ (LVSO) thin film with a thickness of several hundred nanometers, demonstrating that the present method is sensitive to diffusion coefficients down on the order of 10$$^{-12}$$cm$$^{2}$$/s, which is more sensitive by about two orders of magnitude than that previously achieved.

論文

Surrogate reactions research at JAEA/Tokyo Tech

千葉 敏; 西尾 勝久; 牧井 宏之; 有友 嘉浩*; 西中 一朗; 石井 哲朗; 塚田 和明; 浅井 雅人; 古高 和禎; 橋本 慎太郎; et al.

Nuclear Data Sheets, 119, p.229 - 232, 2014/05

http://dx.doi.org/10.1016/j.nds.2014.08.063
 パーセンタイル：100(Physics, Nuclear)

We will present a status of researches in surrogate reaction method using heavy-ions to determine neutron fission and capture cross sections of unstable nuclei. We take advantage of having (1) an electrostatic tandem accelerator which can deliver highly mono-energetic beams of heavy ions, (2) rich experience in in-beam $$gamma$$ spectroscopy, (3) rich experience in measuring fission fragments induced by heavy-ions, (4) nuclear theory and evaluation experiences. We have constructed apparatus to measure fission fragments and $$gamma$$-rays in coincidence with ejectiles by which we can identify the populated compound nuclei. Primarily, we used $$^{18}$$O-induced reactions as well as $$^3$$He-induced reactions. We also investigated conditions under which such measurements lead to correct neutron cross sections. Results of the theoretical researches were published in a series of papers. In this presentation, status of results of the above researches will be summarized.

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