Schmitt, C.*; Lemasson, A.*; Schmidt, K.-H.*; Jhingan, A.*; Biswas, S.*; Kim, Y. H.*; Ramos, D.*; Andreyev, A. N.; Curien, D.*; Ciemala, M.*; et al.
Physical Review Letters, 126(13), p.132502_1 - 132502_6, 2021/04
Isotopic distributions of fragments from fission of the neutron-deficient Hg nuclide are reported. This experimental observable is obtained for the first time in the region around lead using an innovative approach based on inverse kinematics and the coincidence between the large acceptance magnetic spectrometer VAMOS++ and a new detection arm close to the target. The average fragment ratio and prompt neutron multiplicity are derived and compared with current knowledge from actinide fission. A striking consistency emerges, revealing the unexpected dominant role of the proton subsystem with atomic number between the = 28 and 50 magic numbers. The origin of nuclear charge polarization in fission and fragment deformation at scission are discussed.
Vermeulen, 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
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.
Prez Snchez, R.*; Jurado, B.*; Mot, V.*; Roig, O.*; Dupuis, M.*; Bouland, O.*; Denis-Petit, D.*; Marini, P.*; Mathieu, L.*; Tsekhanovich, I.*; et al.
Physical Review Letters, 125(12), p.122502_1 - 122502_5, 2020/09
Reliable neutron-induced-reaction cross sections of unstable nuclei are essential for nuclear astrophysics and applications but their direct measurement is often impossible. The surrogate-reaction method is one of the most promising alternatives to access these cross sections. In this work, we successfully applied the surrogate-reaction method to infer for the first time both the neutron-induced fission and radiative capture cross sections of Pu in a consistent manner from a single measurement. This was achieved by combining simultaneously measured fission and -emission probabilities for the Pu(He, He') surrogate reaction with a calculation of the angular-momentum and parity distributions populated in this reaction. While other experiments measure the probabilities for some selected -ray transitions, we measure the -emission probability. This enlarges the applicability of the surrogate-reaction method.
牧井 宏之; 西尾 勝久; 廣瀬 健太郎; Orlandi, R.; Lguillon, R.; 小川 達彦; Soldner, T.*; Kster, U.*; Pollitt, A.*; Hambsch, F.-J.*; et al.
Physical Review C, 100(4), p.044610_1 - 044610_7, 2019/10
The prompt fission -ray energy spectrum for cold-neutron induced fission of U was measured in the energy range = 0.8 - 20,MeV, by gaining a factor of about 10 in statistics compared to the measurements performed so far. The spectrum exhibits local bump structures at 4,MeV and 6,MeV, and also a broad one at 15,MeV. In order to understand the origins of these bumps, the -ray spectra were calculated using a statistical Hauser-Feshbach model, taking into account the de-excitation of all the possible primary fission fragments. It is shown that the bump at 4,MeV is created by the transitions between the discrete levels in the fragments around Sn, and the bump at 6,MeV mostly comes from the complementary light fragments. It is also indicated that a limited number of nuclides, which have high-spin states at low excitation energies, can contribute to the bump structure around 15,MeV, induced by the transition feeding into the low-lying high-spin states.
Kean, K. R.; 西尾 勝久; 廣瀬 健太郎; Vermeulen, M. J.; 牧井 宏之; Orlandi, R.; 塚田 和明; Andreyev, A. N.; Tsekhanovich, I.*; 千葉 敏*
Physical Review C, 100(1), p.014611_1 - 014611_6, 2019/07
The validity of the multinucleon transfer (MNT) approach for deduction of fission barrier heights was investigated in an experiment carried out at the JAEA tandem accelerator facility. By using the O+Np reaction, fission barrier heights were inferred from fission probabilities of the nuclei Np and Pu produced in the and transfer channels, respectively. The deduced values of fission barriers agree well with the literature data, thus demonstrating the potential of the MNT reactions for obtaining fission-barrier data for nuclei not accessible for fission studies via neutron- or light charged particle-induced reactions.
Tsekhanovich, I.*; Andreyev, A. N.; 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
Fragment mass distributions from fission of the excited compound nucleus Pt have been deduced from the measured fragment velocities. The Pt nucleus was created at the JAEA tandem facility in a complete fusion reaction Ar+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 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, / 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.
牧井 宏之; 西尾 勝久; 廣瀬 健太郎; Orlandi, R.; Lguillon, R.*; 小川 達彦; Soldner, T.*; Hambsch, F.-J.*; Ache, M.*; Astier, A.*; et al.
Nuclear Instruments and Methods in Physics Research A, 906, p.88 - 96, 2018/10
Andel, B.*; Andreyev, A. N.; Antalic, S.*; Barzakh, A.*; Bree, N.*; Cocolios, T. E.*; Comas, V. F.*; Diriken, J.*; Elseviers, J.*; Fedorov, D. V.*; et al.
Physical Review C, 96(5), p.054327_1 - 054327_11, 2017/12
A detailed -decay spectroscopy study of Tl has been performed at ISOLDE (CERN). Z-selective ionization by the Resonance Ionization Laser Ion Source (RILIS) coupled to mass separation provided a high-purity beam of Tl. Fine-structure decays to excited levels in the daughter Au were identified and an -decay scheme of Tl was constructed based on an analysis of - and - - coincidences. Multipolarities of several -ray transitions deexciting levels in Au were determined. Based on the analysis of reduced -decay widths, it was found that all decays are hindered, which signifies a change of configuration between the parent and all daughter states.
廣瀬 健太郎; 西尾 勝久; 田中 翔也*; Lguillon, 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
JAEAタンデム加速器施設で行ったO+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、U, Np、およびPuの核分裂質量分布を励起エネルギー1060MeVにおいて測定した。これらのうち、U, 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。
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
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; Lguillon, 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
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 O beam (9MeV/u) and several actinide target nuclei such as Th, U, Np, Cm. Ejectile nuclei and thus the transfer channels were identified by a newly developed silicon 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.
牧井 宏之; 西尾 勝久; 廣瀬 健太郎; Orlandi, R.; Lguillon, R.; 小川 達彦; Soldner, T.*; Hambsch, F.-J.*; Astier, A.*; Pollitt, A.*; et al.
EPJ Web of Conferences, 146, p.04036_1 - 04036_4, 2017/09
西尾 勝久; 廣瀬 健太郎; Lguillon, 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
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 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 O + U, Th, Cm, Np. The obtained fission fragment mass distributions were reproduced by a model calculation based on a fluctuation dissipation model.
Lguillon, 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
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 O + Th reaction are used to study fission of fourteen nuclei Th, Pa, and 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 Th and 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.
西尾 勝久; Andreyev, A. N.*; Chapman, R.*; Derkx, X.*; Dllmann, C. E.*; Ghys, L.*; Heberger, F. P.*; 廣瀬 健太郎; 池添 博*; Khuyagbaatar, J.*; et al.
Physics Letters B, 748, p.89 - 94, 2015/09
Mass distributions of fission fragments from the compound nuclei Hg and Hg formed in fusion reactions Ar+Sm and Ar+Sm, respectively, were measured at initial excitation energies of (Hg)=,3366 MeV and (Hg)=,4871 MeV. In the fission of Hg, the mass spectra were well reproduced by assuming only an asymmetric-mass division, with most probable light and heavy fragment masses /79101. The mass asymmetry for Hg agrees well with that obtained in the low-energy /EC-delayed fission of Tl, from our earlier ISOLDE(CERN) experiment. Fission of Hg is found to proceed in a similar way, delivering the mass asymmetry of /83107, 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 Hg.
Elseviers, J.*; Andreyev, A. N.*; Huyse, M.*; Van Duppen, P.*; Antalic, S.*; Barzakh, A.*; Bree, N.*; Cocolios, T. E.*; Comas, V. F.*; Diriken, J.*; et al.
Physical Review C, 88(4), p.044321_1 - 044321_13, 2013/10
The detailed analysis of the -delayed fission data of Tl is presented. The experiment was performed by producing a pure beam of Tl by means of highly selective resonance laser ionization followed by mass separation with the ISOLDE isotope separator. A surprising asymmetric mass distribution of fission fragments from Hg, the daughter of Tl decays, was obtained. Here, the energy calibration of the silicon detectors, which is crucial for a proper determination of the fission fragments' energy and mass split, is presented and the total kinetic energy and its dependence on the mass split ratio is discussed. A more precise -delayed fission probability of 3.2(2)10 was deduced.
Andreyev, A. N.*; Liberati, V.*; Antalic, S.*; Ackermann, D.*; Barzakh, A.*; Bree, N.*; Cocolios, T. E.*; Diriken, J.*; Elseviers, J.*; Fedorov, D.*; et al.
Physical Review C, 87(5), p.054311_1 - 054311_8, 2013/05
-decay studies of Tl and its dahghter products Au and Ir were carried out in two complementary experiments at the mass separator ISOLDE (CERN) and velocity filter SHIP (GSI). The nucluesu Au has decay properties of half-life 207 ms and -decay energy 6433 keV. The ground state spins and parities for Au and Ir were determined to be 1/2.
Andreyev, A. N.*; Elseviers, J.*; Huyse, M.*; Van Duppen, P.*; Antalic, S.*; Barzakh, A.*; Bree, N.*; Cocolios, T. E.*; Comas, V. F.*; Diriken, J.*; et al.
Physical Review Letters, 105(25), p.252502_1 - 252502_5, 2010/12
A very exotic process of -delayed fission of Tl is studied in detail by using resonant laser ionization with subsequent mass separation at ISOLDE (CERN). In contrast to common expectations, the fission-fragment mass distribution of the post--decay daughter nucleus Hg (/ = 1.25) is asymmetric. This asymmetry is more surprising since a mass-symmetric split of this extremely neutron-deficient nucleus would lead to two Zr fragments, with magic = 50 and semi-magic = 40. This is a new type of asymmetric fission, not caused by large shell effects related to fragment magic proton and neutron numbers, as observed in the actinide region. The newly-measured branching ratio for -delayed fission of Tl is 3.6(7)10 %.
西尾 勝久; Andreyev, A. N.*; Elseviers, J.*; Huyse, M.*; Van Duppen, P.*; Antalic, S.*; Barzakh, A.*; Bree, N.*; Cocolios, T. E.*; Comas, V. F.*; et al.
no journal, ,
田村 信行; 廣瀬 健太郎; 西尾 勝久; 西中 一朗; 牧井 宏之; Orlandi, R.; Lguillon, R.; Smallcombe, J.; Andreyev, A. N.; 大槻 勤*; et al.
no journal, ,