Yan, S. Q.*; Li, X. Y.*; 西尾 勝久; Lugaro, M.*; Li, Z. H.*; 牧井 宏之; Pignatari, M.*; Wang, Y. B.*; Orlandi, R.; 廣瀬 健太郎; et al.
Astrophysical Journal, 919(2), p.84_1 - 84_7, 2021/10
The long-lived Fe (with a half-life of 2.62 Myr) is a crucial diagnostic of active nucleosynthesis in the Milky Way galaxy and in supernovae near the solar system. The neutron-capture reaction Fe(n,)Fe on Fe (half-life=44.5 days) is the key reaction for the production of Fe in massive stars. This reaction cross section has been previously constrained by the Coulomb dissociation experiment, which offered partial constraint on the E1 -ray strength function but a negligible constraint on the M1 and E2 components. In this work, for the first time, we use the surrogate ratio method to experimentally determine the Fe(n,)Fe cross sections in which all the components are included. We derived a Maxwellian-averaged cross section of 27.53.5 mb at = 30 keV and 13.41.7 mb at = 90 keV, roughly 10%-20% higher than previous estimates. We analyzed the impact of our new reaction rates in nucleosynthesis models of massive stars and found that uncertainties in the production of Fe from the Fe(n,)Fe rate are at most 25. We conclude that stellar physics uncertainties now play a major role in the accurate evaluation of the stellar production of Fe.
Moon, B.*; Jungclaus, A.*; Nadja, H.*; Gargano, A.*; Lozeva, R.*; Moon, C.-B.*; Orlandi, R.; 他66名*
Physical Review C, 103(3), p.034320_1 - 034320_15, 2021/03
At RIKEN RIBF facility, the beta decay of Sb and Sb were studied and several new excited states were assigned to the level schemes of Te and Te. The structure of these Te isotopes deduced from the level scheme is compared with state-of-the-art shell-model calculations using different effective interactions. The comparison with calculations permits to determine the spectroscopic factors and deformation of these isotopes close to doubly magic Sn.
岩佐 直仁*; 石川 竣喜*; 久保野 茂*; 榊原 昂浩*; 小湊 和也*; 西尾 勝久; 松田 誠; 廣瀬 健太郎; 牧井 宏之; Orlandi, R.; et al.
Physical Review C, 103(1), p.015801_1 - 015801_5, 2021/01
The Be(He,)Be()Li reaction was studied at (He)=30 MeV to deduce the branching ratios of of resonant state at 18.91 - 20.1 MeV in Be, which are necessary to extract the Be(, )Li reaction rate relevant to the Be destruction in the big bang nucleosynthesis, from the Li(,)Be reaction cross section. The decay protons from Be to the ground and first excited states in Li were well-separately measured. The ratio of the 19.235-MeV state was deduced to be 3.41.9%. The 19.86- and 20.1-MeV states were found to decay dominantly into the first excited and ground states of Li, respectively.
Vermeulen, M. J.; 西尾 勝久; 廣瀬 健太郎; Kean, K. R.; 牧井 宏之; Orlandi, R.; 塚田 和明; Tsekhanovich, I.*; Andreyev, A. N.; 石崎 翔馬*; et al.
Physical Review C, 102(5), p.054610_1 - 054610_11, 2020/11
Fission fragment mass distributions for 23 nuclei (U, Np, Pu, Am, Cm, and Bk) were measured using the multi-nucleon transfer approach in the reaction of O+Np, and their excitation-energy dependence was obtained up to a maximum of 70 MeV. Among them, the low energy fission of Np, Pu, and Cm is reported for the first time. The experimental data for all the studied nuclei were compared to the Langevin calculations. The calculation which takes into account the effects of multi-chance fission well reproduced the peak-to-valley ratio and mass-asymmetric peak positions of the distributions. The angular momenta given to the fissioning nucleus is also discussed.
Jungclaus, A.*; Keatings, J. M.*; Simpson, G. S.*; Orlandi, R.; 他47名*
Physical Review C, 102(3), p.034324_1 - 034324_11, 2020/09
The decay of Sn was investigated at RIBF, RIKEN. For Sb the first information on excited states was obtained. In the case of Sb and Sb, new gamma-rays were observed. The new experimental results, in combination with state-of-the-art shell-model calculations, provide the first information on the evolution of the 0gand 1d proton single-particle states with increasing neutron number beyond =84.
Bello Garrote, F. L.*; Sahin, E.*; 角田 佑介*; 大塚 孝治*; Grgen, A.*; Orlandi, R.; 他61名*
Physical Review C, 102(3), p.034314_1 - 034314_13, 2020/09
Detailed spectroscopy of neutron-rich odd- Cu isotopes is of great importance for studying the shell evolution in the region of Ni. Excited states in Cu were populated in the decay of Ni isotopes, which were produced by the in-flight fission at RIBF, RIKEN. The Ni isotopes were separated, identified, and implanted in a highly segmented Si detector array for the detection of the -decay electrons, while the delayed rays were detected by an array of HPGe cluster detectors. A level scheme of Cu was built up to 4 MeV, from which the location of the two previously known low-lying isomeric states was clarified. The level structure below 2 MeV was interpreted based on the results of the shell-model calculations and the systematics of odd- Cu isotopes, revealing the evolution of single-particle states in this region.
Gottardo, A.*; de Angelis, G.*; Doornenbal, P.*; Coraggio, L.*; Gargano, A.*; Itaco, N.*; Orlandi, R.; 他52名*
Physical Review C, 102(1), p.014323_1 - 014323_8, 2020/07
Reduced transition probabilities have been measured for the neutron-rich Ni nuclei with relativistic Coulomb excitation performed at the RIKEN Nishina Center. Excitation energies compare well with the result of large-scale shell-model calculations, while values are larger than predicted. This could indicate an increasing contribution of proton excitations across the shell closure when approaching Ni.
Frotscher, A.*; Gmez-Ramos, M.*; Obertelli, A.*; Doornenbal, P.*; Authelet, G.*; 馬場 秀忠*; Orlandi, R.; 他86名*
Physical Review Letters, 125(1), p.012501_1 - 012501_7, 2020/07
Twenty-one two-proton () knock-out cross sections of neutron-rich radioactive isotopes were measured in inverse kinematics using the MINOS time-projection chamber at RIBF, RIKEN. The proton angular distributions, measured for the first time, reveal that the reaction kinematics of the () reaction is consistent with sequential proton collisions within the projectile nucleus.
Orlandi, R.; 廣瀬 健太郎; 矢板 毅; 山上 浩志; 家田 淳一; 神戸 振作; 石川 法人
日本原子力学会誌ATOMO, 62(5), p.280 - 284, 2020/05
Dupont, E.*; Astier, A.*; Petrache, C. M.*; Lv, B. F.*; Deloncle, I.*; Kiener, J.*; Orlandi, R.; 牧井 宏之; 西尾 勝久; 廣瀬 健太郎; et al.
Physical Review C, 101(1), p.014309_1 - 014309_6, 2020/01
Five new 2 levels and one new 3 level were established in Po. The states were populated via the Pb(C, Be) two-proton reaction experiment, performed at the JAEA Tandem in Tokai. A setup combining Ge, LaBr, and Si telescopes was used to detect in-beam -rays and ejectile residues. Two-proton configurations were assigned to all new states. All assignments are strongly supported by shell-model calculations.
牧井 宏之; 西尾 勝久; 廣瀬 健太郎; Orlandi, R.; Lguillon, R.; 小川 達彦; Soldner, T.*; Kster, U.*; Pollitt, A.*; Hambsch, F.-J.*; et al.
Physical Review C, 100(4), p.044610_1 - 044610_7, 2019/10
The prompt fission -ray energy spectrum for cold-neutron induced fission of U was measured in the energy range = 0.8 - 20,MeV, by gaining a factor of about 10 in statistics compared to the measurements performed so far. The spectrum exhibits local bump structures at 4,MeV and 6,MeV, and also a broad one at 15,MeV. In order to understand the origins of these bumps, the -ray spectra were calculated using a statistical Hauser-Feshbach model, taking into account the de-excitation of all the possible primary fission fragments. It is shown that the bump at 4,MeV is created by the transitions between the discrete levels in the fragments around Sn, and the bump at 6,MeV mostly comes from the complementary light fragments. It is also indicated that a limited number of nuclides, which have high-spin states at low excitation energies, can contribute to the bump structure around 15,MeV, induced by the transition feeding into the low-lying high-spin states.
Torres, D. A.*; Chapman, R.*; Kumar, V.*; Hadinia, B.*; Hodsdon, A.*; Labiche, M.*; Liang, X.*; O'Donnell, D.*; Ollier, J.*; Orlandi, R.; et al.
European Physical Journal A, 55(9), p.158_1 - 158_21, 2019/09
Excited states of the rubidium isotopes Rb were studied at the INFN Legnaro National Laboratory. Measurements of the -ray of nuclei produced in binary reactions from the interaction of a beam of 530 MeV Zr ions with a Sn target were complemented by studies of the -rays from nuclei produced in the interaction of a beam of 230 MeV S ions with a thick Yb target. The structure of the yrast states of Rb is discussed within the context of spherical shell-model and cranked Nilsson-Strutinsky calculations.
Xiao, Y.*; Go, S.*; Grzywacz, R.*; Orlandi, R.; Andreyev, A. N.; 浅井 雅人; Bentley, M. A.*; de Angelis, G.*; Gross, C. J.*; Hausladen, P.*; et al.
Physical Review C, 100(3), p.034315_1 - 034315_8, 2019/09
A search for super-allowed decay of N=Z nuclei Te and Xe was carried out using a novel recoil-decay scintillator detector at the tandem accelerator facility at Japan Atomic Energy Agency. Inorganic crystal scintillation material of YAP:Ce (Yttrium Aluminium Perovskite) coupled to position-sensitive photo-multiplier tube (PSPMT) was implemented for the first time in a radioactive decay experiment. Residues from the fusion-evaporation reaction Ni+Fe Xe were separated by the JAEA Recoil Mass Separator (RMS) and implanted into the YAP:Ce crystal. decays of neutron-deficient tellurium isotopes were identified and proton-emission of I was observed. No conclusive evidence was found for the decay chain XeTe Sn within 3 days experiment. The cross section limit of 130 pb was obtained for production of two events of Xe, about an order of magnitude below the expectation based on earlier cross section measurements and HIVAP calculations.
Wrzosek-Lipska, K.*; Rezynkina, K.*; Bree, N.*; Zieliska, M.*; Gaffney, L. P.*; Petts, A.*; Andreyev, A. N.; Bastin, B.*; Bender, M.*; Blazhev, A.*; et al.
European Physical Journal A, 55(8), p.130_1 - 130_23, 2019/08
The neutron-deficient mercury isotopes serve as a classical example of shape coexistence, whereby at low energy near-degenerate nuclear states characterized by different shapes appear. The electromagnetic structure of even-mass Hg isotopes was studied using safe-energy Coulomb excitation of neutron-deficient mercury beams delivered by the REX-ISOLDE facility at CERN. The population of 0, 2, and 4 states was observed in all nuclei under study. Reduced matrix elements coupling populated yrast and non-yrast states were extracted, including their relative signs. These are a sensitive probe of shape coexistence and may be used to validate nuclear models. The experimental results are discussed in terms of mixing of two different configurations and are compared with three different model calculations: the Beyond Mean Field model, the Interacting Boson Model with configuration mixing and the General Bohr Hamiltonian. Partial agreement with experiment was observed, hinting to missing ingredients in the theoretical descriptions.
Vaquero, V.*; Jungclaus, A.*; Rodrguez-Snchez, J. L.*; Tostevin, J. A.*; Doornenbal, P.*; Wimmer, K.*; Chen, S.*; Orlandi, R.; 他26名*
Physics Letters B, 795, p.356 - 361, 2019/08
Inclusive one- and multi-nucleon removal cross sections were measured for several Sn, Sb and Te isotopes beyond the = 82 neutron shell closure at RIBF, RIKEN. The experimental cross sections are compared to predictions from the most recent Liege intranuclear cascade model. Severe discrepancies are observed and are discussed. Also, the measured inclusive one-proton knockout cross section for the semi-magic Sn projectile is compared to eikonal direct reaction theory calculations to assess if the suppression factors to these calculated cross sections are applicable to heavy nuclei.
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
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 O+Np reaction, fission barrier heights were inferred from fission probabilities of the nuclei Np and Pu produced in the and 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.
Chen, Z. Q.*; Li, Z. H.*; Hua, H.*; 渡邉 寛*; Yuan, C. X.*; Zhang, S. Q.*; Lorusso, G.*; Orlandi, R.; 他60名*
Physical Review Letters, 122(21), p.212502_1 - 212502_6, 2019/05
-delayed -ray spectroscopy of the neutron-rich isotopes Ag was carried out at RIBF, RIKEN. The long predicted 1/2 emitting isomers were identified in both nuclei for the first time. The new experimental results extend the systematic trend of energy spacing between the lowest 9/2 and 1/2 levels in Ag isotopes up to N=78, providing a clear signal for the reduction of the Z=40 subshell gap in Ag towards N=82. The tensor force is found to play a key role in the reduction of the Z=40 sub-shell gap.
渡邉 寛*; Wang, H. K.*; Lorusso, G.*; 西村 俊二*; Xu, Z. Y.*; 炭竃 聡之*; Orlandi, R.; 他47名*
Physics Letters B, 792, p.263 - 268, 2019/05
The isotopes Pd and Pd, respectively with 79 and 81 neutrons, are key isotopes to understand the evolution of the N=82 shell closure below Pd. These nuclei were studied at RIBF (RIKEN). New isomeric states with half-lives of 144(4) ns and 39(6) s were assigned spins and parities of (23/2) and (19/2) in Pd and Pd, respectively. The assignment was carried out based on the results of the -ray intensity balance analysis and the measured transition strengths with the aid of a shell-model calculation. The isomoer in Pd was ascribed predominantly to three neutron-hole excitations in the N=50-82 shell. The 19/2 state in Pd is expected to involve the coupling of proton and neutron configurations. The new data will provide important benchmarks for a better understanding of -process nucleosynthesis.
Paul, N.*; Obertelli, A.*; Bertulani, C. A.*; Corsi, A.*; Doornenbal, P.*; Rodriguez-Sanchez, J. L.*; Authelet, G.*; Orlandi, R.; 他84名*
Physical Review Letters, 122(16), p.162503_1 - 162503_7, 2019/04
Fifty-five single nucleon removal cross sections from neutron-rich nuclei impinging on a hydrogen target at about 250 MeV/nucleon were measured at the RIKEN RIBF. Systematically higher cross sections are found for proton removal from nuclei with an even number of protons compared to odd-proton number projectiles for the same separation energy, while no even-odd staggering was observed in case of neutron-removal. These observations are linked to paring correlations in the daughter nuclei and the density of bound levels. The effect is particularly strong in loosely bound nuclei.
Vaquero, V.*; Jungclaus, A.*; Doornenbal, P.*; Wimmer, K.*; Moro, A. M.*; Orlandi, R.; 他28名*
Physical Review C, 99(3), p.034306_1 - 034306_14, 2019/03
The reduced transition probability B(E2; 0) to the first excited 2 state of the neutron-rich nucleus Te, with two protons and two neutrons outside the doubly magic Sn core, was measured via Coulomb excitation at relativistic energies at the RIKEN Radioactive Isotope Beam Factory. In the experiment, Te isotopes impinged on a 950 mg/cm Au target. The measured B(E2) value, 0.191(26) eb, is in good agreement with the result of a recent experiment employing low-energy Coulomb excitation. Because of the high statistics gathered in this work the error of the deduced B(E2) value is dominated by the systematic uncertainties involved in the analysis of Coulomb excitation experiments at beam energies around 150 MeV/u. These uncertainties were assessed for the first time and will be of use for future experiments at RIBF.