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論文

Validation of the multinucleon transfer method for the determination of the fission barrier height

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

 被引用回数:0 パーセンタイル:100(Physics, Nuclear)

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 $$^{18}$$O+$$^{237}$$Np reaction, fission barrier heights were inferred from fission probabilities of the nuclei $$^{239}$$Np and $$^{239,240}$$Pu produced in the $$2n$$ and $$pn/p2n$$ 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.

論文

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

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

 被引用回数:8 パーセンタイル:4.7(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

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

 被引用回数:26 パーセンタイル:7.66(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, 163, p.00041_1 - 00041_6, 2017/11

 被引用回数:1 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

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

 被引用回数:3 パーセンタイル:48.33(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

Cluster-transfer reactions with radioactive beams; A Spectroscopic tool for neutron-rich nuclei

Bottoni, S.*; Leoni, S.*; Fornal, B.*; Raabe, R.*; Rusek, K.*; Benzoni, G.*; Bracco, A.*; Crespi, F. C. L.*; Morales, A. I.*; Bednarczyk, P.*; et al.

Physical Review C, 92(2), p.024322_1 - 024322_8, 2015/08

 被引用回数:14 パーセンタイル:20.76(Physics, Nuclear)

An exploratory experiment was performed at REX-ISOLDE CERN to test the potential of cluster-transfer reactions at the Coulomb barrier as a mechanism to explore the structure of exotic neutron-rich nuclei. The transfer of triton and alpha particles in a reaction of a beam of $$^{98}$$Rb onto a $$^7$$Li target were studied through particle-$$gamma$$ coincidence measurements. The results indicate that such cluster transfer reactions can be an efficient method to investigate the structure of neutron-rich nuclei at medium-high excitation energies and spins.

論文

Low-velocity transient-field technique with radioactive ion beams; $$g$$ factor of the first excited $$2^+$$ state in $$^{72}$$Zn

Illana, A.*; Jungclaus, A.*; Orlandi, R.; Perea, A.*; Bauer, C.*; Briz, J. A.*; Egido, J. L.*; Gernh$"a$user, R.*; Leske, J.*; M$"u$cher, D.*; et al.

Physical Review C, 89(5), p.054316_1 - 054316_11, 2014/05

 被引用回数:9 パーセンタイル:36.75(Physics, Nuclear)

The $$g$$ factor of the first excited state in $$^{72}$$Zn was measured using the transient-field technique in combination with Coulomb excitation. The experiment was ran at REX-ISOLDE, CERN, and the $$gamma$$-ray perturbed angular correlations were measured using 4 triple Germanium clusters of the Miniball array. The experimental result $$g$$(2$$_1^{+}$$) = +0.47(14) is significant to establish the structure of the Zn isotopes near N=40. Comparison with shell-model calculations reveal that to reproduce the measured energies and B(E2) of the Zn isotopes around N=40, both the the proton excitations from the $$f_{7/2}$$ orbit and neutron excitations into the $$g_{9/2}$$ and $$d_{5/2}$$ orbits are essential. Furthermore, beyond-mean-field calculations reveal the need to include the triaxial degree of freedom.

論文

Erosion of $$N$$=20 shell in $$^{33}$$Al investigated through the ground-state electric quadrupole moment

島田 健司*; 上野 秀樹*; Neyens, G.*; 旭 耕一郎*; Balabanski, D. L.*; Daugas, J. M.*; Depuydt, M.*; De Rydt, M.*; Gaudefroy, L.*; Gr$'e$vy, S.*; et al.

Physics Letters B, 714(2-5), p.246 - 250, 2012/08

 被引用回数:6 パーセンタイル:56.95(Astronomy & Astrophysics)

中性子過剰核における魔法数消滅の研究を目的として、フランスGANIL研究所にて、ベータNMR法を用いて中性子過剰核$$^{33}$$Alの電気的四重極モーメント($$Q$$モーメント)の測定を行った。得られた$$Q$$モーメントの値の絶対値は、133(18)$$e$$mbとなった。この実験値を殻模型及び粒子・振動結合模型の二つの理論模型の値と比較した。その結果、中性子数20の閉殻構造消失を考慮に入れていない従来の殻模型計算では、$$Q$$モーメントを過小評価する一方、魔法数消滅を考慮に入れた大規模殻模型計算では実験値を正しく再現した。同様の値が、中性子数20の閉殻構造消失を考慮に入れた粒子・振動結合模型でも得られた。その結果、中性子20の閉殻構造は$$^{33}$$Al核でも相当程度消失していることが判明した。

論文

Precision measurement of the electric quadrupole moment of $$^{31}$$Al and determination of the effective proton charge in the sd-shell

De Rydt, M.*; Neyens, G.*; 旭 耕一郎*; Balabanski, D. L.*; Daugas, J. M.*; Depuydt, M.*; Gaudefroy, L.*; Gr$'e$vy, S.*; 挾間 優佳*; 市川 雄一*; et al.

Physics Letters B, 678(4), p.344 - 349, 2009/07

 被引用回数:13 パーセンタイル:32.72(Astronomy & Astrophysics)

フランスGANIL研究所にて中性子過剰核$$^{31}$$Alを$$^{36}$$Sの核破砕反応により生成し、その基底状態の電気的四重極モーメントをベータNMR法にて初めて測定した。実験で得られたモーメントを機構にてなされたモンテカルロ殻模型計算で求められた値と比較した。実験値で得られた134.0(16)mbに対し、標準的な有効電荷を用いた計算値は155mbとおおむね良い値を与えているものの多少の相違があることがわかった。これまでの磁気モーメントの測定値から、この原子核では魔法数20の殻ギャップを超える励起の確率は小さく、理論計算は良い波動関数を与えていると考えられる。したがって、この相違は有効電荷に帰せられると考えられ、標準的な値よりもやや小さな有効電荷を用いることにより実験値をよく再現することがわかった。この小さな有効電荷は不安定核特有の中性子の緩い束縛と関係すると考えられる。

論文

$$g$$ factor of the exotic $$N=21$$ isotope $$^{34}$$Al; Probing the $$N=20$$ and $$N=28$$ shell gaps at the border of the "island of inversion"

Himpe, P.*; Neyens, G.*; Balabanski, D. L.*; B$'e$lier, G.*; Daugas, J. M.*; de Oliveira Santos, F.*; De Rydt, M.*; Flanagan, K. T.*; Matea, I.*; Morel, P.*; et al.

Physics Letters B, 658(5), p.203 - 208, 2008/01

 被引用回数:37 パーセンタイル:11.07(Astronomy & Astrophysics)

フランスGANILにて中性子過剰核$$^{34}$$Alを生成し、その$$g$$因子の絶対値($$|g|=0.539(2)$$)を初めて測定した。その$$g$$因子の大きさとこれまでのベータ崩壊のデータを照らし合わせて、$$^{34}$$Alの基底状態のスピンパリティは$$4^-$$が妥当であることが示された。この$$g$$因子を殻模型計算と比較した結果、中性子数20の殻ギャップから中性子が励起しないと仮定した計算では説明できず、この核はいわゆる「逆転の島」に入ることがわかった。さらにモンテカルロ殻模型によって励起を取り入れた計算をしたところ、この$$g$$因子は、中性子数20のギャップのみならず$$f$$軌道と$$p$$軌道間のギャップである中性子数28の殻ギャップの大きさにも敏感であることがわかった。

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

Fission fragment mass distributions of Np, Pu and Am isotopes utilizing multi-nucleon transfer reactions

Vermeulen, M. J.; 西尾 勝久; 牧井 宏之; 廣瀬 健太郎; Orlandi, R.; 塚田 和明; 千葉 敏*; Andreyev, A.*

no journal, , 

FFMD are interpreted in terms of symmetric and asymmetric modes. The current work looks at the excitation energy dependence of the FFMD of various actinide nuclei, with the aim to provide more information regarding the distribution of waste products following the transmutation of actinide waste in accelerator driven systems (ADS)The JAEA-Tokai Tandem accelerator facility was utilized for the current work, supplying an 18O beam with an energy of 162 MeV. This beam impinged on a target of $$^{237}$$Np, leading to many excited compound nuclei (CN; $$^{237,238,239}$$Np, $$^{238,239,240}$$Pu, $$^{241,242,243}$$Am), via MNT reactions, which then undergo fission. CN and their excitation energies were identified by detecting ejectiles with a silicon $$Delta$$E-E telescope. Fission fragments were detected in coincidence with two multi-wire proportional counters (MWPCs), and FFs masses were determined by a kinematic consideration. Preliminary results show the transition from asymmetric fission to asymmetric fission as CN excitation energy increases. All the measured nuclei investigated in this experiment showed similar behavior as will be shown at the meeting.

口頭

$$gamma$$-ray spectroscopy of the heaviest nuclei at the JAEA-Tokai Tandem laboratory, using $$^{249}$$Cf and $$^{254}$$Es targets

Orlandi, R.; 牧井 宏之; 西尾 勝久; 廣瀬 健太郎; 塚田 和明; 浅井 雅人; 永目 諭一郎; 佐藤 哲也; 豊嶋 厚史; Vermeulen, M. J.; et al.

no journal, , 

The spectroscopy of heavy nuclei near the $$N$$=152 and $$N$$=162 deformed shell gaps provides precious information to improve current predictions of super-heavy elements in the Island of Stability. Due to deformation, in fact, substates of spherical orbits in the Island of Stability can be found in the Fermi level in these lighter nuclei. At the JAEA-Tokai Tandem accelerator, the first in-beam $$gamma$$-ray spectroscopy of $$^{252}$$Fm ($$Z$$=100, $$N$$=162) was attempted. $$^{252}$$Fm was produced via the multi-nucleon transfer reaction $$^{249}$$Cf ($$^{12}$$C,$$^{9}$$Be) reaction. The particle-gamma detection setup comprised an array of Si detectors to identify the reaction ejectiles, and a mixed array of four Germanium and four LaBr$$_3$$(Ce) detectors, with an absolute photopeak efficiency of nearly 30%. The X-rays of fermium and candidate transitions for the ground state rotational band of $$^{252}$$Fm were observed. The implications of this test measurement and future projects involving a $$^{254}$$Es target are presented.

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

$$^{254}$$Es標的を用いて生成する中性子過剰Fm領域核の自発核分裂の測定

浅井 雅人; 塚田 和明; 廣瀬 健太郎; 豊嶋 厚史; 富塚 知博; Chiera, N. M.; 伊藤 由太; 牧井 宏之; 永目 諭一郎; 西尾 勝久; et al.

no journal, , 

$$^{256}$$Fm, $$^{258}$$Fm, $$^{259}$$Lrの自発核分裂の測定を、原子力機構タンデム加速器施設において$$^{254}$$Es標的を用いて行った。これら3核種は、非対称核分裂, 全運動エネルギー(TKE)の大きい対称核分裂、TKEの小さい対称核分裂という、それぞれ異なる核分裂特性を示し、そのメカニズムも大きく異なる。これらの違いがどのように生じるか、非常に興味深い。$$^{256,258}$$Fmは$$^{254}$$Es標的と$$^{18}$$Oビームを用いた多核子移行反応で合成し、$$^{259}$$Lrは$$^{248}$$Cm($$^{15}$$N,4n)融合蒸発反応で合成した。生成核をガスジェット結合型オンライン同位体分離装置で質量分離し、回転円盤型$$alpha$$・核分裂片測定装置に運んで測定した。実験で得られた核分裂片の質量数とTKEの分布から、$$^{256}$$Fm, $$^{258}$$Fm, $$^{259}$$Lrの自発核分裂のメカニズムの違いについて議論する。

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.

口頭

$$^{254}$$Es標的を用いた中性子過剰Fm同位体の自発核分裂測定

浅井 雅人; 塚田 和明; 廣瀬 健太郎; 豊嶋 厚史; 富塚 知博; Chiera, N. M.; 伊藤 由太; 牧井 宏之; 永目 諭一郎; 西尾 勝久; et al.

no journal, , 

原子力機構タンデム加速器施設において、中性子過剰重アクチノイド核$$^{256}$$Fm, $$^{258}$$Fm, $$^{259}$$Lrの自発核分裂を測定した。$$^{256}$$Fmと$$^{258}$$Fmは、$$^{18}$$Oビームと半減期276日の非常に稀少な$$^{254}$$Es標的を用いた多核子移行反応で合成した。核反応生成物はオンライン同位体分離装置(ISOL)で質量分離した。典型的な質量非対称な核分裂から非常にシャープな質量対称分裂への遷移が、$$^{256}$$Fmと$$^{258}$$Fmの間で明瞭に観測された。一方、$$^{259}$$Lrの自発核分裂では、3種類の異なる核分裂モードが混在していることが明らかになった。

口頭

Spontaneous fission measurements for neutron-rich Fm and Lr isotopes using $$^{254}$$Es target

浅井 雅人; 塚田 和明; 廣瀬 健太郎; 豊嶋 厚史*; 富塚 知博*; Chiera, N. M.*; 伊藤 由太; 牧井 宏之; 永目 諭一郎*; 西尾 勝久; et al.

no journal, , 

中性子過剰フェルミウム同位体$$^{256}$$Fm,$$^{258}$$Fm及びローレンシウム同位体$$^{259}$$Lrをそれぞれ$$^{254}$$Es標的を用いた重イオン多核子移行反応及び$$^{248}$$Cm標的と$$^{15}$$Nビームを用いた重イオン核融合反応で合成し、それらをオンライン同位体分離装置ISOLで同位体分離した後、自発核分裂を測定した。$$^{256}$$Fmの自発核分裂の質量分布が非対称分布なのに対して$$^{258}$$Fmでは非常に分布幅の狭い対称分布であることを確認し、過去の実験結果を再検証した。一方$$^{259}$$Lrでは対称分布と非対称分布が混在している様子が観測された。質量分布と全運動エネルギー分布の測定結果からこれらの分裂メカニズムについて考察した。

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