Devaraja, H. M.*; Heinz, S.*; Beliuskina, O.*; Hofmann, S.*; Hornung, C.*; Mnzenberg, G.*; Ackermann, D.*; Gupta, M.*; Gambhir, Y. K.*; Henderson, R. A.*; et al.
European Physical Journal A, 55(2), p.25_1 - 25_9, 2019/02
The results for nuclei above curium, produced in multi-nucleon transfer reactions of Ca+Cm at the velocity filter SHIP of GSI Darmstadt, are presented. Spontaneous fission and activities have been used to study the population of nuclei with lifetimes ranging from few milliseconds to several days. We observed several, relatively neutron-rich isotopes with atomic numbers Z 98; among them a weak 224 millisecond activity which we tentatively attributed to No. The measured cross-sections of the observed nuclei give hope that multi-nucleon transfer reactions are a way to reach new neutron-rich heavy and superheavy nuclei, which are not accessible in other reactions. We compare our results with data from earlier experiments and discuss limitations and future perspectives of the method.
加治 大哉*; 森田 浩介*; 森本 幸司*; 羽場 宏光*; 浅井 雅人; 藤田 訓裕*; Gan, Z.*; Geissel, H.*; 長谷部 裕雄*; Hofmann, S.*; et al.
Journal of the Physical Society of Japan, 86(3), p.034201_1 - 034201_7, 2017/03
理化学研究所のガス充填型反跳核分離装置GARISを用いてCa + Cm Lv融合反応を調べた。116番元素Lv, Lvと思われる核反応生成物に起因するアルファ線と自発核分裂の崩壊連鎖が7事象観測された。崩壊連鎖中に観測された原子核の性質は過去の報告値とよく一致したが、1つの崩壊連鎖で一部矛盾が観測された。これはCnの新しい自発核分裂分岐比の存在、あるいは新同位体Lv生成の可能性を示唆するものと思われる。
Hofmann, S.*; Heinz, S.*; Mann, R.*; Maurer, J.*; Mnzenberg, G.*; Antalic, S.*; Barth, W.*; Burkhard, K. G.*; Dahl, L.*; Eberhardt, K.*; et al.
European Physical Journal A, 52(6), p.180_1 - 180_34, 2016/06
The reaction Cr+Cm was investigated at the velocity filter SHIP at GSI with the intention to study production and decay properties of isotopes of element 120. Three correlated signals were measured, which occurred within a period of 279 ms. The heights of the signals correspond with the expectations for a decay sequence starting with an isotope of element 120. However, a complete decay chain cannot be established, since a signal from the implantation of the evaporation residue cannot be identified unambiguously. Measured properties of the event chain are discussed in detail. The result is compared with theoretical predictions. Previously measured decay properties of even element super-heavy nuclei were compiled in order to find arguments for an assignment from the systematics of experimental data. In the course of this review, a few tentatively assigned data could be corrected. New interpretations are given for results which could not be assigned definitely in previous studies. The discussion revealed that the cross-section for production of element 120 could be high enough so that a successful experiment seems possible with presently available techniques. However, a continuation of the experiment at SHIP for a necessary confirmation of the results obtained in a relatively short irradiation of five weeks is not possible at GSI presently. In the summary and outlook section we also present concepts for the continuation of research in the field of super-heavy nuclei.
Andel, B.*; Andreyev, A.; Antalic, S.*; Heberger, F. P.*; Ackermann, D.*; Hofmann, S.*; Huyse, M.*; Kalaninov, Z.*; Kindler, B.*; Kojouharov, I.*; et al.
Physical Review C, 93(6), p.064316_1 - 064316_12, 2016/06
Isomeric states in Po and Po were studied at the velocity filter SHIP. The isotopes were produced in the fusion-evaporation reactions Pr(Fe, )Po and Sm(V, )Po. Several new -ray transitions were attributed to the isomers and - coincidences for both isomers were studied for the first time. The 459-keV transition earlier, tentatively proposed as de-exciting the isomeric level in Po, was replaced by a new 248-keV transition, and the spin of this isomer was reassigned from (11) to (10). The de-excitation of the (11) isomeric level in Po by the 154-keV transition was confirmed and a parallel de-excitation by a 733-keV (E3) transition to (8) level of the ground-state band was suggested. Moreover, side feeding to the (4) level of the ground-state band was proposed. The paper also discusses strengths of transitions de-exciting 11 isomers in neighboring Po and Pb isotopes.
Hofmann, S.*; Heinz, S.*; Mann, R.*; Maurer, J.*; Mnzenberg, G.*; Antalic, S.*; Barth, W.*; Dahl, L.*; Eberhardt, K.*; Grzywacz, R.*; et al.
European Physical Journal A, 52(4), p.116_1 - 116_12, 2016/04
Shell-correction energies of super-heavy nuclei are approximated by using Q values of measured decay chains. Five decay chains were analyzed, which start at the isotopes Fl, 118, Lv, Lv and Lv. The data are compared with predictions of macroscopic-microscopic models. Fission barriers are estimated that can be used to eliminate uncertainties in partial fission half-lives and in calculations of evaporation-residue cross-sections. In that calculations, fission probability of the compound nucleus is a major factor contributing to the total cross-section. The data also provide constraints on the cross-sections of capture and quasi-fission in the entrance channel of the fusion reaction. Arguments are presented that fusion reactions for synthesis of isotopes of elements 118 and 120 may have higher cross-sections than assumed so far.
Devaraja, H. M.*; Heinz, S.*; Beliuskina, O.*; Comas, V. F.*; Hofmann, S.*; Hornung, C.*; Mnzenberg, G.*; 西尾 勝久; Ackermann, D.*; Gambhir, Y. K.*; et al.
Physics Letters B, 748, p.199 - 203, 2015/09
In deep inelastic multinucleon transfer reactions of Ca +Cm we observed about 100 residual nuclei with proton numbers between Z =82 and Z =100. Among them, there are five new neutron-deficient isotopes: U, Np, Am, Am and Bk. As separator for the transfer products we used the velocity filter SHIP of GSI while the isotope identification was performed via the -decay chains of the nuclei. These first results reveal that multinucleon transfer reactions together with here applied fast and sensitive separation and detection techniques are promising for the synthesis of new isotopes in the region of heaviest nuclei.
Andreyev, A. N.*; Huyse, M.*; Van Duppen, P.*; Qi, C.*; Liotta, R. J.*; Antalic, S.*; Ackermann, D.*; Franchoo, S.*; Heberger, F. P.*; Hofmann, S.*; et al.
Physical Review Letters, 110(24), p.242502_1 - 242502_5, 2013/06
-decay data for more than 20 nuclei of the most neutron-deificient isotopes in the region from lead to thorium was obtained. The combined analysis allowed us for the first time to clearly show that crossing the Z=82 shell to higher proton numbers strongly accelerates the decay. The analysis support the conjecture that both the N=126 and Z=82 shell closures stongly influence the -formation probability.
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.
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
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.
Andreyev, A. N.*; Antalic, S.*; Ackermann, D.*; Bianco, L.*; Franchoo, S.*; Heinz, S.*; Heberger, F. P.*; Hofmann, S.*; Huyse, M.*; Kalaninov, Z.*; et al.
Physical Review C, 87(1), p.014317_1 - 014317_8, 2013/01
By using the recoil-fission correlation technique, the exotic process of beta-delayed fission (DF) was unambiguously identified in the very neutron-deficient nuclei At in experiments at the velocity filter SHIP at Gesellschaft fr Schwerionenforschung (GSI). The upper limits for the total kinetic energy release in fission of Po, being the daughter of At after decay, were estimated. The possibility of an unusually high DF probability At is discussed.
Lane, J. F. W.*; Andreyev, A. N.*; Antalic, S.*; Ackermann, D.*; Gerl, J.*; Heberger, F. P.*; Hofmann, S.*; Huyse, M.*; Kettunen, H.*; Kleinbhl, A.*; et al.
Physical Review C, 87(1), p.014318_1 - 014318_7, 2013/01
By using the technique of correlating implanted evaporation residues and their subsequent fission decay, -delayed fission (DF) of Bi has been identified for the first time and DF of Bi has been unambiguously confirmed. The experiments were performed at the velocity filter SHIP (GSI, Darmstadt). The DF probabilities for both nuclides were qualitatively estimated, and, in particular indications for a large value in the case of Bi are regarded.
Khuyagbaatar, J.*; 西尾 勝久; Hofmann, S.*; Ackermann, D.*; Block, M.*; Heinz, S.*; Heberger, 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
The influence of the structure of projectile and target nuclei on the capture cross-sections was investigated for the reactions S+Pb and S+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 S than with S. This observation is explained by a stronger coupling to the vibrational states in the reactions with S. Comparing the capture cross-sections and the evaporation-residue cross-sections for the reactions S+Pb and S+Pb, both yielding the same compound nucleus Cf, it is shown that the latter reaction has a lower fusion probability.
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
Fission cross sections and fission fragment mass distributions were measured in the reactions of Ca + U and Ca + 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 Ca + U using a statistical model showed that sub-barrier fusion reaction can be applied to form the element 112.
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
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.
Heberger, F. P.*; Antalic, S.*; Ackermann, D.*; Kalaninov, Z.*; Heinz, S.*; Hofmann, S.*; Streicher, B.*; Kindler, B.*; Kojouharov, I.*; Kuusiniemi, P.*; et al.
European Physical Journal A, 48(5), p.75_1 - 75_9, 2012/05
Nuclear structure and decay of the isotope No and its decay products Fm and Md were investigated by means of - spectroscopy. Besides the established strong transitions from the 9/2 Nilsson level in Fm, populated predominantly by the decay of No, into the ground-state(gs) rotational band, a couple of weaker lines were observed and placed into the Fm level scheme. The transition from the 7/2 level in Es, populated by the decay of Md, into the 9/2 member of the gs rotational band, so far established for other odd-mass Es isotopes, was observed clearly. The GEANT4 simulations were performed to investigate the influence of energy summing between particles and conversion electrons (CE) on the shape of the spectra at different implantation energies, leading to evidence for a weak decay branch of No into the gs of Fm or the ground-state rotational band, respectively.
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 (Internet), 17, p.09005_1 - 09005_4, 2011/10
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.
Antalic, S.*; Heberger, F. P.*; Ackermann, D.*; Heinz, S.*; Hofmann, S.*; Kalaninov, Z.*; Kindler, B.*; Khuyagbaatar, J.*; Kojouharov, I.*; Kuusiniemi, P.*; et al.
European Physical Journal A, 47(5), p.62_1 - 62_12, 2011/05
Nuclear structure and decay of isomer in No were investigated. The isotope was produced by the reaction Ca+Pb. The excitation energy of the known single-particle isomeric state (5/2) was measured by delayed coincidence between -rays and implanted evaporation residues and was placed into the level scheme. In addition, decay of a high-lying multi-quasiparticle isomer in No was studied using e- coincidence measurements. A rotational band populated by its de-excitation was identified in No. A new isomeric state in Fm was observed and a partial-level scheme for this isotope is suggested. In addition transitions from excited levels are reproduced for Md.
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
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
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; 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
Results on the measurements of (1) evaporation residue (ER) cross-sections for Si, S + U and of (2) fission fragment mass distributions for Si,S, Ar + 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 Si + U, the ER cross-section for Sg(5n) suggested no fusion hindance at above-barrier energy, whereas the one for 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 S + U, the ER cross-sections for Hs(5n) and 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 Si,S, Ar + U.