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論文

Charge radii and electromagnetic moments of $$^{195-211}$$At

Cubiss, J.*; Andreyev, A.; 光岡 真一*; 永目 諭一郎; 西尾 勝久; 太田 周也*; 若林 泰生*; 他60名*

Physical Review C, 97(5), p.054327_1 - 054327_19, 2018/05

 被引用回数:5 パーセンタイル:8.84(Physics, Nuclear)

Hyperfine-structure parameters and isotope shifts of $$^{195-211}$$At have been measured for the first time at CERN-ISOLDE, using the in-source resonance-ionization spectroscopy method. The hyperfine structures of isotopes were recorded using a triad of experimental techniques for monitoring the photo-ion current. The Multi-Reflection Time-of-Flight Mass Spectrometer, in connection with a high-resolution electron multiplier, was used as an ion-counting setup for isotopes that either were affected by strong isobaric contamination or possessed a long half-life; the ISOLDE Faraday cups were used for cases with high-intensity beams; and the Windmill decay station was used for short-lived, predominantly $$alpha$$-decaying nuclei. The electromagnetic moments and changes in the mean-square charge radii of the astatine nuclei have been extracted from the measured hyperfine-structure constants and isotope shifts. This was only made possible by dedicated state-of-the-art large-scale atomic computations of the electronic factors and the specific mass shift of atomic transitions in astatine that are needed for these extractions. By comparison with systematics, it was possible to assess the reliability of the results of these calculations and their ascribed uncertainties. A strong deviation in the ground-state mean-square charge radii of the lightest astatine isotopes, from the trend of the (spherical) lead isotopes, is interpreted as the result of an onset of deformation. This behavior bears a resemblance to the deviation observed in the isotonic polonium isotopes. Cases for shape coexistence have been identified in $$^{197,199}$$At, for which a significant difference in the charge radii for ground (9/2$$^{-}$$) and isomeric (1/2$$^{+}$$) states has been observed.

論文

$$beta$$-delayed fission and $$alpha$$ decay of $$^{196}$$At

Truesdale, V. L.*; Andreyev, A.; Ghys, L.*; Huyse, M.*; Van Duppen, P.*; Sels, S.*; Andel, B.*; Antalic, S.*; Barzakh, A.*; Capponi, L.*; et al.

Physical Review C, 94(3), p.034308_1 - 034308_11, 2016/09

 被引用回数:5 パーセンタイル:36.63(Physics, Nuclear)

A nuclear-decay spectroscopy study of the neutron-deficient isotope $$^{196}$$At is reported where an isotopically pure beam was produced using the selective Resonance Ionization Laser Ion Source and On-Line Isotope Mass Separator (CERN). The fine-structure $$alpha$$ decay of $$^{196}$$At allowed the low-energy excited states in the daughter nucleus $$^{192}$$Bi to be investigated. A $$beta$$-delayed fission study of $$^{196}$$At was also performed. A mixture of symmetric and asymmetric fission-fragment mass distributions of the daughter isotope $$^{196}$$Po (populated by $$beta$$ decay of $$^{196}$$At) was deduced based on the measured fission-fragment energies. A $$beta$$DF probability $$P_{rm beta DF}$$($$^{196}$$At) = 9(1)$$times$$10$$^{-5}$$ was determined.

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

 パーセンタイル:100

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

 被引用回数:11 パーセンタイル:35.22(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

New result in the production and decay of an isotope, $$^{278}$$113 of the 113th element

森田 浩介*; 森本 幸司*; 加治 大哉*; 羽場 宏光*; 大関 和貴*; 工藤 祐生*; 住田 貴之*; 若林 泰生*; 米田 晃*; 田中 謙伍*; et al.

Journal of the Physical Society of Japan, 81(10), p.103201_1 - 103201_4, 2012/10

 被引用回数:111 パーセンタイル:2.38(Physics, Multidisciplinary)

113番元素である$$^{278}$$113を$$^{209}$$Bi標的に$$^{70}$$Znビームを照射する実験により合成した。観測したのは6連鎖の$$alpha$$崩壊で、そのうち連鎖の5番目と6番目は既知である$$^{262}$$Db及び$$^{258}$$Lrの崩壊エネルギーと崩壊時間と非常によく一致した。この意味するところは、その連鎖を構成する核種が$$^{278}$$113, $$^{274}$$Rg (Z=111), $$^{270}$$Mt (Z=109), $$^{266}$$Bh (Z=107), $$^{262}$$Db (Z=105)及び$$^{258}$$Lr (Z=103)であることを示している。本結果と2004年, 2007年に報告した結果と併せて、113番元素である$$^{278}$$113を曖昧さなく生成・同定したことを強く結論付ける結果となった。

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

 被引用回数:43 パーセンタイル:6.26(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

Tilted-foil technique for producing a spin-polarized radioactive isotope beam

平山 賀一*; 三原 基嗣*; 渡辺 裕*; Jeong, S. C.*; 宮武 宇也*; 百田 佐多夫*; 橋本 尚志*; 今井 伸明*; 松多 健策*; 石山 博恒*; et al.

European Physical Journal A, 48(5), p.54_1 - 54_10, 2012/05

 被引用回数:2 パーセンタイル:77.83(Physics, Nuclear)

The tilted-foil method for producing spin-polarized radioactive isotope beams has been studied for the application to nuclear physics and materials science, using the radioactive nucleus $$^8$$Li produced at the Tokai Radioactive Ion Accelerator Complex (TRIAC). We successfully produced polarization in a $$^8$$Li beam using 15 thin polystyrene foils fabricated especially for this purpose. A systematic study of the nuclear polarization as a function of the number of foils, beam energy, tilt angles and foil material has been performed, confirming the features of the tilted-foil technique experimentally. The contributions made to the nuclear polarization of $$^8$$Li nuclei by the atomic states was investigated.

論文

GEM-MSTPC; An Active-target type detector in low-pressure He/CO$$_{2}$$ mixed gas

石山 博恒*; 山口 香菜子*; 溝井 浩*; 渡辺 裕*; Das, S. K.*; 橋本 尚志*; 宮武 宇也*; 平山 賀一*; 今井 伸明*; 小柳津 充広*; et al.

Journal of Instrumentation (Internet), 7(3), p.C03036_1 - C03036_14, 2012/03

 被引用回数:6 パーセンタイル:57.36(Instruments & Instrumentation)

不安定核ビームを用いた低エネルギー反応の研究に向けて、低圧力のHe/CO$$_{2}$$混合ガスで動作するガス検出器の開発を行った。高入射率に対応するため、400-$$mu$$m厚のgas electron multiplier(THGEM)を比例計数管として使用することし、最大毎秒10$$^{5}$$個の$$^{12}$$Cビームを用いてテストを行った。テスト結果からTHGEMを用いたガス検出器が高入射率に対応できることを確認した。

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 (Internet), 17, p.09005_1 - 09005_4, 2011/10

 被引用回数:1 パーセンタイル:46.63

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

福島第一原発事故時の環境放射線モニタリングの経験から

光岡 真一

核データニュース(インターネット), (100), p.27 - 30, 2011/10

原子力機構では、震災発生直後から理事長を本部長とする機構対策本部を設置し、福島原発事故対策統合本部の特別プロジェクトや原子力安全委員会等への専門家の派遣による技術的助言及び科学的知見の提供を行うとともに、環境放射線のモニタリングや試料分析、住民への相談対応やスクリーニングなどの支援活動を原子力緊急時支援・研修センターを中心に各拠点やOBとも連携を取りながら総力を挙げて行ってきた。そして5月はじめには福島支援本部を新設し、原発事故の最終的な収束に向けた中・長期的な課題解決に貢献するための本格的な体制を構築した。このなかで、20km圏外での環境モニタリング及び土壌サンプリング、20km圏内への一時帰宅者支援及びスクリーニング活動、健康電話相談に従事しており、これらの活動の様子を紹介する。

論文

Proton resonance elastic scattering in inverse kinematics on the medium heavy nucleus $$^{68}$$Zn

今井 伸明*; 平山 賀一*; 石山 博恒*; Jeong, S.-C.*; 宮武 宇也*; 渡辺 裕*; 牧井 宏之; 光岡 真一; 長江 大輔*; 西中 一朗; et al.

European Physical Journal A, 46(2), p.157 - 160, 2010/11

 被引用回数:2 パーセンタイル:74.1(Physics, Nuclear)

An isobaric analog resonance of $$^{69}$$Zn was studied by the resonance elastic scattering of $$p(^{68}Zn,p)$$ with a 5.5-MeV/nucleon $$^{68}$$Zn beam and a thick polyethylene target. The excitation function of the differential cross section of proton elastic scattering was measured around 0 degrees in the laboratory frame by the thick target inverse kinematics method. The angular momentum, and proton and total widths of the resonance assigned using an $$R$$-matrix calculation are in good agreement with earlier measurements performed using normal kinematics, demonstrating that the thick target inverse kinematics method is a useful tool for studying the single particle structures of neutron-rich nuclei.

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

 被引用回数:54 パーセンタイル:4.71(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

Barrier distribution of quasi-elastic backward scattering in very heavy reaction systems

光岡 真一; 池添 博; 西尾 勝久; 渡辺 裕*; Jeong, S. C.*; 石山 博恒*; 平山 賀一*; 今井 伸明*; 宮武 宇也

International Journal of Modern Physics E, 19(5&6), p.989 - 996, 2010/07

 パーセンタイル:100(Physics, Nuclear)

原子力科学研究所タンデムブースター加速器からの重イオンビーム$$^{48}$$Ti, $$^{54}$$Cr, $$^{56}$$Fe, $$^{64}$$Ni, $$^{70}$$Znを薄膜標的$$^{208}$$Pbに照射し、172$$^{circ}$$, 168$$^{circ}$$, 162$$^{circ}$$に後方散乱される準弾性散乱断面積を測定した。入射エネルギーを1.5MeVごとに変えながら測定した励起関数を1階微分することにより、超重元素104-112番元素を合成する冷たい融合反応における融合障壁分布を実験的に導出した。これにより測定された融合障壁は、従来用いられてきた理論値より5-10MeV程度低いことがわかった。また障壁分布の形状は、接近時の励起効果を考慮したチャンネル結合計算結果と良い一致を示すことがわかった。最近、さらに重い反応系$$^{76}$$Ge, $$^{86}$$Kr+$$^{208}$$Pbについても実験を行い、同様の結果が得られた。

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

 被引用回数:3 パーセンタイル:21.76

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 (Internet), 2, p.10001_1 - 10001_3, 2010/03

 被引用回数:1 パーセンタイル:45.47

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

 被引用回数:1 パーセンタイル:83.74(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

 被引用回数:35 パーセンタイル:8.74(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

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

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

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.

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