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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：50 パーセンタイル：91.08(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

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. N.; Vermeulen, M. J.; et al.

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

https://doi.org/10.1016/j.nima.2016.12.021
 被引用回数：5 パーセンタイル：44.54(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

https://doi.org/10.1016/j.physletb.2016.08.010
 被引用回数：40 パーセンタイル：92.94(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.

報告書

JT-60中性粒子入射加熱装置の解体

秋野 昇; 遠藤 安栄; 花田 磨砂也; 河合 視己人*; 椛澤 稔; 菊池 勝美*; 小島 有志; 小又 将夫; 藻垣 和彦; 根本 修司; et al.

JAEA-Technology 2014-042, 73 Pages, 2015/02

JAEA-Technology-2014-042.pdf:15.1MB

日欧の国際共同プロジェクトであるJT-60SA計画に従い、JT-60実験棟本体室・組立室及び周辺区域に設置されている中性粒子入射加熱装置(NBI加熱装置)の解体・撤去、及びその後の保管管理のための収納を、2009年11月に開始し計画通りに2012年1月に終了した。本報告は、NBI加熱装置の解体・収納について報告する。

論文

In-beam fissio study at JAEA for heavy element synthesis

西尾 勝久; 池添 博; Hofmann, S.*; Ackermann, D.*; 有友 嘉浩*; Comas, V. F.*; D$"u$llmann, Ch. E.*; Heinz, S.*; Heredia, J. A.*; He${ss}$berger, F. P.*; et al.

AIP Conference Proceedings 1524, p.68 - 72, 2013/04

https://doi.org/10.1063/1.4801679
 被引用回数：0 パーセンタイル：0.04(Physics, Nuclear)

Fission fragment mass and kinetic energies distributions were measured in the heavy-ion induced reactions using $$^{238}$$U target nucleus at the energies around the Coulomb barrier. We observed strong variation of the fragment mass distribution with incident energy, which was explained by an energy dependence of the probabilities for fusion and quasifission. A calculation based on a fluctuation-dissipation model was carried out to determine the fusion probability in the reactions of $$^{30}$$Si+$$^{238}$$U and $$^{34}$$S+$$^{238}$$U. The fusion probabilities were consistent with those determied from the evaporation residue cross sections for both reactions, showing that in-beam fission measurement and analysis can give a reasonable estimation for the cross sections to produce super-heavy nuclei. We also discss the results for in-beam fission measurement of $$^{48}$$Ca+$$^{238}$$U.

論文

Evidence for hindrance in fusion between sulfur and lead nuclei

Khuyagbaatar, J.*; 西尾 勝久; Hofmann, S.*; Ackermann, D.*; Block, M.*; Heinz, S.*; He${ss}$berger, F. P.*; 廣瀬 健太郎; 池添 博; Kindler, B.*; et al.

Physical Review C, 86(6), p.064602_1 - 064602_6, 2012/12

https://doi.org/10.1103/PhysRevC.86.064602
 被引用回数：25 パーセンタイル：77.08(Physics, Nuclear)

The influence of the structure of projectile and target nuclei on the capture cross-sections was investigated for the reactions $$^{34}$$S+$$^{204,206,208}$$Pb and $$^{36}$$S+$$^{204,206,208}$$Pb. Capture cross-sections were deduced by measuring the fission fragments using multi-wire proportional counters. An enhancement of the capture cross-sections relative to an one-dimensional barrier penetration model was observed for all reactions at energies below the interaction barriers. The enhancement is larger in the case of reactions with $$^{34}$$S than with $$^{36}$$S. This observation is explained by a stronger coupling to the vibrational states in the reactions with $$^{34}$$S. Comparing the capture cross-sections and the evaporation-residue cross-sections for the reactions $$^{36}$$S+$$^{206}$$Pb and $$^{34}$$S+$$^{208}$$Pb, both yielding the same compound nucleus $$^{242}$$Cf, it is shown that the latter reaction has a lower fusion probability.

論文

Fusion probabilities in the reactions $$^{40,48}$$Ca + $$^{238}$$U at energies around the Coulomb barrier

西尾 勝久; 光岡 真一; 西中 一朗; 牧井 宏之; 若林 泰生*; 池添 博; 廣瀬 健太郎*; 大槻 勤*; 有友 嘉浩*; Hofmann, S.*

Physical Review C, 86(3), p.034608_1 - 034608_6, 2012/09

https://doi.org/10.1103/PhysRevC.86.034608
 被引用回数：78 パーセンタイル：95.38(Physics, Nuclear)

Fission cross sections and fission fragment mass distributions were measured in the reactions of $$^{40}$$Ca + $$^{238}$$U and $$^{48}$$Ca + $$^{238}$$U at energies around the Coulomb barrier. Fusion probabilities were calculated based on the fluctuation dissipation model. The measured mass distributions for both reactions showed an asymmetric shape at low incident energies, whereas the distribution changed to a flat shape at higher energies. The variation of the mass distribution is explained by a change of the ratio between fusion and qasifission with nuclear orientation. The calculation reproduced the mass distributions and their energy dependence. The trajectories for fusion-fission were used to determine the fusion probability. Fusion probabilities for both reactions are identical as function of the center-of-mass energy, but they differ when plotted as function of the excitation energy. The calculated evaporation residue cross sections for the reaction $$^{48}$$Ca + $$^{238}$$U using a statistical model showed that sub-barrier fusion reaction can be applied to form the element 112.

論文

Investigation of fission properties and evaporation residue measurement in the reactions using $$^{238}$$U target nucleus

西尾 勝久; 池添 博; Hofmann, S.*; Ackermann, D.*; Antalic, S.*; 有友 嘉浩; Comas, V. F.*; D$"u$llmann, Ch. E.*; Gorshkov, A.*; Graeger, R.*; et al.

EPJ Web of Conferences, 17, p.09005_1 - 09005_4, 2011/10

https://doi.org/10.1051/epjconf/20111709005
 被引用回数：1 パーセンタイル：47.57(Physics, Nuclear)

Fission fragment mass distributions after full momentum transfer of the projectile were measured in the reactions using a $$^{238}$$U target nucleus bombarded by $$^{30}$$Si, $$^{31}$$P, $$^{34,36}$$S, $$^{40}$$Ar, $$^{40,48}$$Ca projectiles. We observed a strong variation of the distribution as function of bombarding energy. The results were interpreted by the effects of nuclear deformation of the target nucleus on the competition between fusion and quasifission. The symmetric fission includes fusion-fission, wheres as the asymmetric fission represents quasifission. The fusion probabilities were determined with the help of fluctuation-dissipation model. The estimated evaporation residue cross sections ($$^{263,264}$$Sg and $$^{267,268}$$Hs) produced in $$^{30}$$Si + $$^{238}$$U and $$^{34}$$S+$$^{238}$$U reproduced the experimental data.

論文

Nuclear orientation in the reaction $$^{34}$$S+$$^{238}$$U and synthesis of the new isotope $$^{268}$$Hs

西尾 勝久; Hofmann, S.*; He${ss}$berger, F. P.*; Ackermann, D.*; Antalic, S.*; 有友 嘉浩; Comas, V. F.*; D$"u$llmann, Ch. E.*; Gorshkov, A.*; Graeger, R.*; et al.

Physical Review C, 82(2), p.024611_1 - 024611_9, 2010/08

https://doi.org/10.1103/PhysRevC.82.024611
 被引用回数：79 パーセンタイル：96.03(Physics, Nuclear)

Synthesis of isotopes of the element hassium was studied using the reaction $$^{34}$$S+$$^{238}$$U$$rightarrow$$$$^{272}$$Hs*. At a kinetic energy of 163.0 MeV in the center of mass system we observed one $$alpha$$-decay chain starting at the isotope $$^{267}$$Hs. The cross-section was 1.8$$^{+4.2}_{-1.5}$$pb. At 152.0 MeV one decay of the new isotope $$^{268}$$Hs was observed. It decays with a half-life of 0.38$$^{+1.8}_{-0.17}$$s by 9479$$pm$$16 keV $$alpha$$-particle emission. Spontaneous fission of the daughter nucleus $$^{264}$$Sg was confirmed. The measured cross-section was 0.54$$^{+1.3}_{-0.45}$$pb. In-beam measurements of fission fragment mass distributions were performed to obtain information on the fusion probability at various orientation of the deformed target nucleus. The distributions changed from symmetry to asymmetry when the beam energy was changed from above-barrier to sub-barrier values, indicating orientation effects on fusion and/or quasifission. It was found that the distribution of symmetric mass fragments originates not only from fusion-fission, but has a strong component from quasifission. This result significantly influences the interpretation of data obtained from measurements of symmetric mass distributions with respect to extracting evaporation residue cross-sections.

論文

Effects of nuclear orientation on fusion and fission process for reactions using uranium target nuclei

西尾 勝久; 池添 博; 光岡 真一; 西中 一朗; 牧井 宏之; 渡辺 裕*; 永目 諭一郎; 大槻 勤*; 廣瀬 健太郎*; Hofmann, S.*

AIP Conference Proceedings 1224, p.301 - 310, 2010/04

https://doi.org/10.1063/1.3431429
 被引用回数：5 パーセンタイル：84.69(Physics, Nuclear)

Results on the measurements of (1) evaporation residue (ER) cross-sections for $$^{30}$$Si, $$^{34}$$S + $$^{238}$$U and of (2) fission fragment mass distributions for $$^{30}$$Si,$$^{34,36}$$S, $$^{40}$$Ar + $$^{238}$$U will be discussed. Measurement of ER cross-section was carried out at GSI by using the velocity filter SHIP. Measurement of fission fragment mass distributions was made by using the JAEA tandem accelerator. In the reaction $$^{30}$$Si + $$^{238}$$U, the ER cross-section for $$^{263}$$Sg(5n) suggested no fusion hindance at above-barrier energy, whereas the one for $$^{264}$$Sg(4n) suggested competition between fusion and quasi-fission at sub-barrier energy. This conclusion is consistent with the measured fragment mass distributions, where the asymmetric fission component associated with quasi-fission appears only at sub-barrier energies. In the reaction of $$^{34}$$S + $$^{238}$$U, the ER cross-sections for $$^{267}$$Hs(5n) and $$^{268}$$Hs(4n, new isotope) suggested fusion hindrance both for above- and sub-barrier energies. With the results of fission fragment mass distributions, it is found that quasi-fission has symmetric fission components when projectile mass is relatively large. We will also discuss the variation of the fragment mass distributions for $$^{30}$$Si,$$^{34,36}$$S, $$^{40}$$Ar + $$^{238}$$U.

論文

Effects of nuclear orientation on fusion and fission in the reaction using $$^{238}$$U target nucleus

西尾 勝久; 池添 博; 光岡 真一; 西中 一朗; 永目 諭一郎; 大槻 勤*; 廣瀬 健太郎*; Hofmann, S.*

EPJ Web of Conferences, 2, p.10001_1 - 10001_3, 2010/03

https://doi.org/10.1051/epjconf/20100210001
 被引用回数：0 パーセンタイル：0.07(Physics, Nuclear)

We have measured the (1) evaporation residue (ER) cross-sections for $$^{30}$$Si, $$^{34}$$S + $$^{238}$$U and (2) fission fragment mass distributions for $$^{30}$$Si,$$^{34,36}$$S, $$^{40}$$Ar. Measurement of ER cross-section was carried out at GSI by using the velocity filter SHIP. Measurement of fission fragment mass distribution was made by using the JAEA tandem accelerator. In the reaction $$^{30}$$Si + $$^{238}$$U, the ER cross-section for $$^{263}$$Sg(5n) suggested no fusion hindrance at above-barrier energy, whereas the one for $$^{264}$$Sg(4n) suggested competition between fusion and fission at sub-barrier energy. This conclusion is consistent with the measured fragment mass distributions, where the asymmetric fission component associated with quasi-fission appears only at sub-barrier energies. In the reaction of $$^{34}$$S + $$^{238}$$U, the ER cross-sections for $$^{267}$$Hs(5n) and $$^{268}$$Hs(4n, new isotope) suggested fusion hindrance both for above- and sub-barrier energies. With the results of fission fragment mass distributions, it is found that quasi-fission has symmetric fission components when projectile mass is relatively large. We will also discuss the variation of the fragment mass distributions for $$^{30}$$Si,$$^{34,36}$$S, $$^{40}$$Ar + $$^{238}$$U.

論文

Dependence of barrier distribution and fusion-fission process on entrance channel

池添 博; 光岡 真一; 西尾 勝久; 渡辺 裕*; Jeong, S. C.*; 大槻 勤*; 廣瀬 健太郎*

Nuclear Physics A, 834(1-4), p.172c - 175c, 2010/03

https://doi.org/10.1016/j.nuclphysa.2009.12.031
 被引用回数：1 パーセンタイル：13.85(Physics, Nuclear)

重い原子核間のクーロン障壁は衝突時に核の励起効果や核子の移行過程が結合して、幅を持って分布する。クーロン障壁分布を$$^{208}$$Pb標的に$$^{48}$$Ti, $$^{54}$$Cr, $$^{56}$$Fe, $$^{64}$$Ni, $$^{70}$$Zn, $$^{76}$$Ge, $$^{86}$$Krを衝突させる反応系で実験的に導出した。その結果、障壁の中心値は簡単なクーロンパラメータでよくスケールされること、分布の幅は$$^{208}$$Pbの8重極振動モードの結合と核子移行反応の結合で説明できること、さらに、導出した障壁は原子核同士の融合障壁とは異なること、がわかった。また、変形核に球形核が衝突する場合、変形核の長軸側での衝突は原子核同士の融合に向かわず、質量の非対象な準核分裂過程に向かうことを、ウラン標的に$$^{30}$$Si, $$^{36}$$S, $$^{40}$$Arを衝突させる反応実験で明らかにした。

論文

Evidence for quasifission in the sub-barrier reaction of $$^{30}$$Si+$$^{238}$$U

西尾 勝久; 池添 博; 西中 一朗; 光岡 真一; 廣瀬 健太郎*; 大槻 勤*; 渡辺 裕*; 有友 嘉浩*; Hofmann, S.*

Physical Review C, 82(4), p.044604_1 - 044604_5, 2010/00

https://doi.org/10.1103/PhysRevC.82.044604
 被引用回数：48 パーセンタイル：91.32(Physics, Nuclear)

Fragment mass distributions for fission after full momentum transfer were measured for the reaction $$^{30}$$Si,+,$$^{238}$$U at bombarding energies around the Coulomb barrier. At energies above the Bass barrier, the mass distributions were Gaussian with mass symmetry. An asymmetric fission channel with mass $$A_{rm L}/A_{rm H}$$,$$approx$$,90$$/$$178 emerged at the sub-barrier energies, where competition between fusion and quasifission was suggested from the measured evaporation residue (ER) cross-section produced in fusion $$^{30}$$Si,+,$$^{238}$$U. We thus conclude the asymmetric channel is attributed to quasifission. The observed mass asymmetry is significantly smaller than those observed in actinide targets bombarded with heavier projectile, which suggests that the system $$^{30}$$Si,+,$$^{238}$$U approaches the shape of compound nucleus before disintegrating as quasifission.

論文

Effects of nuclear orientation on fission fragment mass distributions in the reactions using actinide target nuclei

西尾 勝久; 池添 博; 光岡 真一; 西中 一朗; 牧井 宏之; 渡辺 裕*; 永目 諭一郎; 大槻 勤*; 廣瀬 健太郎*; Hofmann, S.*

AIP Conference Proceedings 1175, p.111 - 118, 2009/10

https://doi.org/10.1063/1.3258209

Fission fragment properties for the reactions involving actinide target nuclei have been investigated at the JAEA tandem facility. The results showed firstly the appearance of new fission channels. The experimental data are useful for the theoretical study to produce super heavy elements. Also the new fission channels suggested the possible production of the neutron rich nuclei by taking advantage of the new fission channels.

論文

Effects of nuclear orientation on fission fragment mass distributions in the reactions using actinide target nuclei

西尾 勝久; 池添 博; 光岡 真一; 西中 一朗; 牧井 宏之; 渡辺 裕*; 永目 諭一郎; 大槻 勤*; 廣瀬 健太郎*; Hofmann, S.*

AIP Conference Proceedings 1175, p.111 - 118, 2009/10

https://doi.org/10.1063/1.3258209

The influence of nuclear deformation of $$^{238}$$U target nucleus on fusion and fission process was investigated. The study was motivated by larger cross-sections to produce super-heavy nuclei in reactions using actinide target nuclei, compared to those using lead or bismuth target nuclei. We have measured fission fragment mass distributions in the reaction of $$^{30}$$Si,$$^{31}$$P,$$^{34,36}$$S,$$^{40}$$Ar + $$^{238}$$U at JAEA tandem facility. We observed strong variation of the distributions on bombarding energy of projectiles, which indicates that competition between fusion and fission is sensitive to the colliding angle of the projectile to the symmetric axis of $$^{238}$$U. We also measured the evaporation residue cross-sections for $$^{30}$$Si+$$^{238}$$U and $$^{34}$$S+$$^{238}$$U as a direct evidence for fusion. The experiment was carried out at GSI. The results showed that fusion is much hindered in the subbarrier energy, where projectile collides only on the pollar side of the $$^{238}$$U nucleus, whereas the equatorial collision has smaller fusion hindrance. These results indicate that the initial touching configuration influence the subsequent reaction process.

論文

Effects of nuclear orientation on fusion and fission process in heavy ion reactions

西尾 勝久; 池添 博; 光岡 真一; 西中 一朗; 渡辺 裕*; 永目 諭一郎; 大槻 勤*; 廣瀬 健太郎*; Hofmann, S.*

AIP Conference Proceedings 1120 (Internet), p.275 - 279, 2009/05

https://doi.org/10.1063/1.3141660

Effects of nuclear deformation of $$^{238}$$U on fusion and fission was investigated in the reactions of $$^{30}$$Si+$$^{238}$$U and $$^{36}$$S + $$^{238}$$U. From the measurement of evaporation residue cross-sections for $$^{30}$$Si+$$^{238}$$U, carried out at GSI, it is concluded that in the sub-barrier region competition between fusion and quasi-fission was suggested whereas at the above barrier region fusion is the main process after the system is captured inside the Coulomb barrier. The fission fragment mass distributions were measured in $$^{30}$$Si+$$^{238}$$U and $$^{36}$$S+$$^{238}$$U at the JAEA tandem facility. Symmetric fission was observed at the above-barrier region, showing the fusion-fission character. In decreasing the energy to the sub-barrier, the asymmetric fission starts to dominate, showing the signature of quasi-fission. The results suggest that the equatorial collision results in fusion whereas the polar collision results in quasi-fission.

論文

A New measurement of the astrophysical $$^8$$Li(d,t)$$^7$$Li reaction

橋本 尚志; 石山 博恒*; 渡辺 裕*; 平山 賀一*; 今井 伸明*; 宮武 宇也; Jeong, S.-C.*; 田中 雅彦*; 吉川 宣治*; 野村 亨*; et al.

Physics Letters B, 674(4-5), p.276 - 280, 2009/04

https://doi.org/10.1016/j.physletb.2009.03.031
 被引用回数：7 パーセンタイル：47.15(Astronomy & Astrophysics)

$$^8$$Li(d,t)$$^7$$Li反応の反応断面積を重心系で1.2から0.3MeVのエネルギーで7点直接測定した。これらのエネルギーは1$$sim$$3$$times$$10$$^9$$Kのガモフピーク領域をカバーする。重心系で0.8MeVのエネルギーで断面積の増大が観測され、これは複合核である$$^{10}$$Beの22.4MeVの励起状態の寄与によると考えられる。また、この寄与によって天体核反応率は1$$times$$10$$^9$$Kで従来用いられていた値よりも1桁大きいことが明らかとなった。

論文

Effects of nuclear orientation on fission fragment mass distributions in the reactions of $$^{34,36}$$S+$$^{238}$$U

西尾 勝久; 池添 博; 光岡 真一; 西中 一朗; 渡辺 裕*; 永目 諭一郎; 大槻 勤*; 廣瀬 健太郎*; Hofmann, S.*

AIP Conference Proceedings 1098, p.289 - 294, 2009/03

https://doi.org/10.1063/1.3108831

Fragment mass distributions for fission after full momentum transfer were measured for the reaction $$^{36,34}$$S,+,$$^{238}$$U at bombarding energies around the Coulomb barrier. The experiment was carried out by using the sulfur beams supplied by the JAEA tandem accelerator. The experimental data revealed a transition from symmetry to asymmetry mass distributions when the beam energies were decreased from above-barrier to sub-barrier values. The main components of the asymmetric mass distribution are at $$A$$=200 and $$A=$$74. The asymmetric fission is attributed to quasifission of the reacting system at polar collisions, whereas the symmetric fission originates from the compound nucleus produced in equatorial collisions. The results suggest a strong influence of orientation effects of the deformed target nuclei on fusion.

論文

Orientation effects of deformed $$^{238}$$U target nuclei on the fusion probability for the heavy element synthesis

西尾 勝久; Hofmann, S.*; 池添 博; He${ss}$berger, F. P.*; Ackermann, D.*; Antalic, S.*; Comas, V. F.*; Gan, Z.*; Heinz, S.*; Heredia, J. A.*; et al.

Nuclear Physics A, 805(1-4), p.516 - 518, 2008/06

The effects of the orientation of the deformed $$^{238}$$U target nuclei were investigated in the reaction of $$^{30}$$Si+$$^{238}$$U. The cross-sections of the system to overcome the Coulomb barrier were determined by measuring the fission cross-sections at JAEA-tandem accelerator, from which the Coulomb barrier height for the collision of $$^{30}$$Si to the polar side and the equatorial side of $$^{238}$$U were determined. The evaporation residue (ER) cross-sections were determined at the velocity filter SHIP of GSI. Significant enhancement of the cross-sections of $$^{264}$$Sg(4n) in the sub-barrier energy indicates the lowering of the Coulomb barrier at the Polar collisions. However, competition between fusion and quasifission was implied. The cross-sections for $$^{263}$$Sg(5n) measured at the above barrier energy indicated that there is no significant fusion hindrance at the equatorial collisions. In this contribution, the systematic behavior of the orientation effects of $$^{238}$$U is discussed by using additionally the data of $$^{16}$$O+$$^{238}$$U and $$^{48}$$Ca+$$^{238}$$U.

論文

Effects of nuclear orientation on the mass distribution of fission fragments in the reaction of $$^{36}$$S + $$^{238}$$U

西尾 勝久; 池添 博; 光岡 真一; 西中 一朗; 永目 諭一郎; 渡辺 裕*; 大槻 勤*; 廣瀬 健太郎*; Hofmann, S.*

Physical Review C, 77(6), p.064607_1 - 064607_5, 2008/06

https://doi.org/10.1103/PhysRevC.77.064607
 被引用回数：121 パーセンタイル：98.15(Physics, Nuclear)

Fragment mass distributions for fission after full momentum transfer were measured for the reaction $$^{36}$$S + $$^{238}$$U at bombarding energies around the Coulomb barrier. The data revealed a transition from symmetry to asymmetry mass distributions when the beam energies were decreased from above-barrier to sub-barrier values. The main components of the asymmetric mass distribution are at $$A_{rm H} approx $$ 200 and $$A_{rm L} approx $$ 74. The asymmetric fission is attributed to quasifission of the reacting system at polar collisions, whereas the symmetric fission originates from the compound nucleus produced in equatorial collisions. The results suggest a strong influence of orientation effects of the deformed target nuclei on fusion.

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