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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
被引用回数:3 パーセンタイル:26.98(Physics, Nuclear)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.
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
被引用回数:38 パーセンタイル:88.71(Physics, Nuclear)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.
西尾 勝久; 池添 博; Hofmann, S.*; Ackermann, D.*; 有友 嘉浩*; Comas, V. F.*; Dllmann, Ch. E.*; Heinz, S.*; Heredia, J. A.*; Heberger, F. P.*; et al.
AIP Conference Proceedings 1524, p.68 - 72, 2013/04
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 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 Si+U and S+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 Ca+U.
Hofmann, S.*; Heinz, S.*; Mann, R.*; Maurer, J.*; Khuyagbaatar, J.*; Ackermann, D.*; Antalic, S.*; Barth, B.*; Block, M.*; Burkhard, H. G.*; et al.
European Physical Journal A, 48(5), p.62_1 - 62_23, 2012/05
被引用回数:167 パーセンタイル:98.85(Physics, Nuclear)The synthesis of element 116 in the reactions of Ca+Cm was studied at the GSI-SHIP. Four decay chains from the isotope 116 and one decay 116 were detected at the reaction leading to the excitation energy of 40.9 MeV. The cross sections were 3.4 and 0.9 pb, respectively. The decay character reproduced the reported data at FLNR, Russia. In the decay chain, we observed the higher -particle energy in the decay of 114, which suggested the population and the decay of a quasiparitcle state.
西尾 勝久; 池添 博; Hofmann, S.*; Ackermann, D.*; Antalic, S.*; 有友 嘉浩; Comas, V. F.*; Dllmann, Ch. E.*; Gorshkov, A.*; Graeger, R.*; et al.
EPJ Web of Conferences, 17, p.09005_1 - 09005_4, 2011/10
被引用回数:1 パーセンタイル:47.43(Physics, Nuclear)Fission fragment mass distributions after full momentum transfer of the projectile were measured in the reactions using a U target nucleus bombarded by Si, P, S, Ar, 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 (Sg and Hs) produced in Si + U and S+U reproduced the experimental data.
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
被引用回数:189 パーセンタイル:97.20(Physics, Multidisciplinary)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 %.
Khuyagbaatar, J.*; Heberger, F. P.*; Hofmann, S.*; Ackermann, D.*; Comas, V. F.*; Heinz, S.*; Heredia, J. A.*; Kindler, B.*; Kojouharov, I.*; Lommel, B.*; et al.
European Physical Journal A, 46(1), p.59 - 67, 2010/10
被引用回数:27 パーセンタイル:81.08(Physics, Nuclear)The isotope Cf were produced in irradiation of Pb targets with S ions at bombarding energies close to the Coulomb barrier. For the isotope Cf a spontaneous fission branching of 0.015 was determined. The new isotope Cm was produced by decay of Cf. It decays with 6954-keV particle emission, and half-life was determined to be 410 s. The -decay of Cf was observed for the first time, and the particle energy was 8081 keV. For the isotope Cm a half-life 23 s was measured for the first time.
西尾 勝久; Hofmann, S.*; Heberger, F. P.*; Ackermann, D.*; Antalic, S.*; 有友 嘉浩; Comas, V. F.*; Dllmann, 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:79 パーセンタイル:95.97(Physics, Nuclear)Synthesis of isotopes of the element hassium was studied using the reaction S+UHs*. At a kinetic energy of 163.0 MeV in the center of mass system we observed one -decay chain starting at the isotope Hs. The cross-section was 1.8pb. At 152.0 MeV one decay of the new isotope Hs was observed. It decays with a half-life of 0.38s by 947916 keV -particle emission. Spontaneous fission of the daughter nucleus Sg was confirmed. The measured cross-section was 0.54pb. 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.
西尾 勝久; Hofmann, S.*; 池添 博; Heberger, 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 U target nuclei were investigated in the reaction of Si+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 Si to the polar side and the equatorial side of 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 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 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 U is discussed by using additionally the data of O+U and Ca+U.
西尾 勝久; Hofmann, S.*; 池添 博; Heberger, F. P.*; Ackermann, D.*; Antalic, S.*; Comas, V. F.*; Gan, Z.*; Heinz, S.*; Heredia, J. A.*; et al.
Journal of Nuclear and Radiochemical Sciences, 8(2), p.73 - 78, 2007/10
Effects of the prolate deformation of U on fusion were studied in the reaction Si + U at bombarding energies close to the Coulomb barrier. The fission cross section was measured at JAEA tandem accelerator to see the enhancement of the cross section in the subbarrier energy due to the lowering of the Coulomb barrier at the collision of the projectile to polar side of U. Evaporation residue cross sections were measured at UNILAC of GSI by using the velocity filter SHIP to determine the fusion probability. In the subbarrier region, we could produce isotope Sg by 4n channel, but fusion hindrance was implied in the analysis. At above barrier energies, we produced Sg by 5n channel. The analysis suggests that there is no fusion hindrance at the equatorial collisions.
Hofmann, S.*; Ackermann, D.*; Antalic, S.*; Burkhard, H. G.*; Comas, V. F.*; Dressler, R.*; Gan, Z.*; Heinz, S.*; Heredia, J. A.*; Heberger, F. P.*; et al.
European Physical Journal A, 32(3), p.251 - 260, 2007/06
被引用回数:262 パーセンタイル:99.70(Physics, Nuclear)The fusion reaction of Ca projectiles withU target nuclei was studied at the velocity filter SHIP of GSI. Two decay chains were measured, which fully confirm data that were previously assigned to the isotope 112 in experiments at the Flerov Laboratory in Dubna. Two other events are consistent with a 50% spontaneous fission (SF) branch of this isotope. The mean value obtained for the half-life of 112 is (6.9) s, the energy is (9.5200.015) MeV, and the total kinetic energy (TKE) of SF is (23814) MeV. The half-life of the decay daughter nucleus Ds is (0.18) s, and the TKE of SF is (210) MeV. The cross-section deduced from all four events is (0.72) pb, measured at an excitation energy of 34.6 MeV of the compound nucleus 112.
西尾 勝久; Hofmann, S.*; Heberger, F. P.*; Ackermann, D.*; Antalic, S.*; Comas, V. F.*; Gan, Z.*; Heinz, S.*; Heredia, J. A.*; 池添 博; et al.
AIP Conference Proceedings 891, p.71 - 79, 2007/03
重イオン融合反応Si+UによりSg同位体を合成し、この生成断面積を調べた。実験は、ドイツ重イオン研究所(GSI)で行った。反応エネルギーE=144MeVにおいて、Sgから始まる3つの崩壊連鎖を観測し、断面積67pbを得た。サブバリヤエネルギーE=133MeVで、新同位体Sgを3つ合成し、断面積10pbを得た。これは自発核分裂で崩壊し、半減期は120msであった。これら断面積を統計モデル計算と比較した。融合過程においては、Uの変形を取り入れたチャンネル結合法で捕獲断面積を決定した。この値は、原子力機構のタンデム加速器を用いて行ったSi+Uの核分裂断面積とよく一致した。E=133MeVでの断面積の値は、一次元モデルに比べて10倍大きな値であり、ウランの変形によって断面積が増加することがわかった。しかし、計算との不一致から、準核分裂が何割か存在することが示唆された。クーロン障壁より高いエネルギーE=144MeVではSiはUの赤道面と接触できる。Sgの生成断面積67pbは、統計モデル計算値によく一致し、融合に阻害がなかった。これは、赤道面衝突が融合に有利であることを示唆している。
西尾 勝久; Hofmann, S.*; Heberger, F. P.*; Ackermann, D.*; Antalic, S.*; Comas, V. F.*; Gan, Z.*; Heinz, S.*; Heredia, J. A.*; 池添 博; et al.
European Physical Journal A, 29(3), p.281 - 287, 2006/09
被引用回数:64 パーセンタイル:93.91(Physics, Nuclear)重イオン融合反応Si+UによりSg同位体を合成し、この生成断面積を調べた。実験は、ドイツ重イオン研究所(GSI)で行った。反応エネルギーE=144MeVにおいて、Sgから始まる3つの崩壊連鎖を観測した。断面積は、67pbであった。サブバリヤエネルギーE=133MeVで、新同位体Sgを3つ合成し断面積10pbを得た。これは自発核分裂で崩壊し、半減期は120msであった。これら断面積を統計モデル計算と比較した。融合過程においては、Uの変形を取り入れたチャンネル結合法で捕獲断面積を決定した。この値は、原子力機構のタンデム加速器を用いて行ったSi+Uの核分裂断面積とよく一致した。E=133MeVでの断面積の値は、一次元モデルに比べて10倍大きな値であり、ウランの変形によるサブバリヤでの断面積の増加で説明できた。しかし、計算との不一致から、準核分裂が何割か存在することが示唆された。クーロン障壁より高いエネルギーE=144MeVではSiはUの赤道面と接触できる。Sgの生成断面積65pbは、統計モデル計算値によく一致し、融合に阻害がなかった。これは、赤道面衝突が融合に有利であることを示唆している。
廣瀬 健太郎; 西尾 勝久; 西中 一朗; 牧井 宏之; 池添 博*; Orlandi, R.; Lguillon, R.; 塚田 和明; 浅井 雅人; 永目 諭一郎; et al.
no journal, ,
原子核に重イオンを衝突させたとき、入射核が標的核から多数の核子を受け取り、複合核を形成せずに核分裂(準核分裂)する場合や、複合核を形成して核分裂(融合核分裂)する場合がある。これらを弁別する手法を確立するために、原子力機構タンデム加速器施設を使用し、準核分裂および融合核分裂のメカニズムを調べてきた。Uに種々の原子核を衝突させ、合成した複合核の核分裂質量分布を測定した。取得した質量分布を、動的計算と比較した結果、よい一致を得た。この理論では原子核のポテンシャル上を系がどのように時間発展していくかを追跡できるため、融合核分裂が全核分裂にしめる割合(融合確率)を計算できる。得られた融合確率により、重元素合成断面積の実験結果をよく再現できた。すなわち重イオン入射反応において系が複合核を形成するか否かを知るための手法を確立した。さらに我々は、多核子移行反応を用いた核分裂の研究を行っている。これまでに、Th, U, Np, Cm標的にOビームを照射し、広い核種・励起エネルギー領域で複合核を合成し、その核分裂における質量分布などを測定した。一度の測定で約20核種を合成できることが多核子移行反応の利点であり、その半数程度の核種の核分裂質量分布は本研究により初めて得られた。これまでに一部の核種では質量分布の測定結果を先の理論計算により再現できることを確認した。今後さらなる比較を行い、理論計算の改良・適用領域の拡大が期待できる。
西尾 勝久; Hofmann, S.*; Heberger, F. P.*; Ackermann, D.*; Antalic, S.*; Comas, V. F.*; Dllmann, Ch. E.*; Gorshkov, A.*; Graeger, R.*; Heinz, S.*; et al.
no journal, ,
S+Uのサブバリヤエネルギー融合反応により、超重元素(Z=108)の新同位体Hsを合成した。実験に先立ち、原子力機構タンデム加速器においてこの反応の核分裂断面積の励起関数を測定するとともに、核分裂片の質量数分布を測定した。モデル計算により、サブバリヤ領域でも融合反応確率が存在することを予測した。Hsの合成実験は、ドイツGSIの線形加速器UNILACに設置された反跳生成核分離装置SHIPを用いて行った。合成に成功し、断面積として0.54pbを得た。Hsは崩壊核種で、半減期0.38 sであることがわかった。
西尾 勝久; 光岡 真一; 池添 博; Hofmann, S.*; Heberger, F. P.*; Ackermann, D.*; Antalic, S.*; Comas, V. F.*; Gan, Z.*; Heinz, S.*; et al.
no journal, ,
重イオン融合反応Si+UによりSg同位体を合成し、この生成断面積を調べた。実験は、ドイツ重イオン研究所(GSI)で行った。反応エネルギーE=144MeVにおいて、Sgから始まる3つの崩壊連鎖を観測した。断面積は、67pbであった。サブバリヤエネルギーE=133MeVで新同位体Sgを3つ合成し、断面積10pbを得た。これは自発核分裂で崩壊し、半減期は120msであった。これら断面積を統計モデル計算と比較した。融合過程においては、Uの変形を取り入れたチャンネル結合法で捕獲断面積を決定した。この値は、原子力機構のタンデム加速器を用いて行ったSi+Uの核分裂断面積とよく一致した。E=133MeVでの断面積の値は、一次元モデルに比べて10倍大きな値であり、ウランの変形によってサブバリヤで断面積が増加していることを明らかにした。しかし、計算との不一致から、準核分裂が何割か存在することが示唆された。クーロン障壁より高いエネルギーE=144MeVではSiはUの赤道面と接触できる。Sgの生成断面積67pbは、統計モデル計算値によく一致し、融合に阻害がなかった。これは、赤道面衝突が融合に有利であることを示唆している。
西尾 勝久; Hofmann, S.*; 池添 博; Ackermann, D.*; Antalic, S.*; Comas, V. F.*; Gan, Z.*; Heinz, S.*; Heredia, J. A.*; Heberger, F. P.*; et al.
no journal, ,
Effects of the prolate deformation of U on the fusion probability was investigated in the reactions of O+U and Si+U. The experiment was carried out at the JAEA tandem accelerator and GSI of Darmstadt. For O+U, the evaporation residue cross-sections for fermium isotopes were measured down to deep sub-barrier. The results indicate that the projectile O fuses from every colliding angle to the symmetric axis of the U target nucleus. In the reacion of Si+U, fusion hindrance was implied in the deep sub-barrier energies, but no fusion hindrance was suggested at the above barrier energy where the collision on the equatorial side of U starts to contribute. The results suggest that the equatorial collisions has advantage to produce heavy elements in the reaction using heavier projectiles.
西尾 勝久; 池添 博; Hofmann, S.*; Ackermann, D.*; Antalic, S.*; 有友 嘉浩; Comas, V. F.*; Dllmann, Ch. E.*; Gorshkov, A.*; Graeger, R.*; et al.
no journal, ,
In-beam measurement of fission-fragment mass distributions in S + U were performed to obtain information on the fusion probability at various orientations of the deformed target nucleus. The experiment was carried out at the JAEA tandem facility. The distributions changed from symmetry to asymmetry when the beam energy was changed from above-barrier to sub-barrier values, indicating the orientation effects on fusion and/or quasifission. We also produced evaporation residues (ERs) as a direct evidence for fusion. The experiment was carried out at GSI by using the velocity filter SHIP. At above-barrier energy, the isotope Hs (5n) was produced and the cross section of 1.8 pb was obtained. It was concluded that the distribution of symmetric mass fragments originate not only from fusion fission, but has a strong component from quasifission. At sub-barrier energy, we produced a new isotope Hs (4n) with the cross section 0.54 pb. We obtained the fusion probability enough to produce SHN. These results were supported by a calculation based on a dynamical description using Langevin equation, where fusion and quasifission were separately determined. The effects of projectile mass (charge) on fusion from the measured fission properties of Si, P, S, Ar, Ca + U are obtained.
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, ,
陽子過剰な原子核Hgの低励起エネルギー核分裂を測定した。CERN-ISOLDEにおいてTlをアイソトープ分離し、このベータ崩壊によって娘核Hgを励起さることで、この核分裂を観測した(ベータ崩壊遅延核分裂)。核分裂特性を調べたところ、中性子数50の閉殻を有するZr原子核は生成されず、質量数80と100に収率の最大を有する非対称な核分裂を示した。また、原子力機構タンデム加速器において、陽子過剰原子核のインビーム核分裂実験を行った。この結果、ウランなど従来の核分裂と異なり、励起エネルギーが増加しても質量非対称度が変化しないことがわかった。