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論文

Transition strengths in the neutron-rich $$^{73,74,75}$$Ni isotopes

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 $$^{73,74,75}$$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 $$B(E2)$$ values are larger than predicted. This could indicate an increasing contribution of proton excitations across the $$Z=28$$ shell closure when approaching $$^{78}$$Ni.

論文

Sequential nature of ($$p,3p$$) two-proton knockout from neutron-rich nuclei

Frotscher, A.*; G$'o$mez-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 ($$p,3p$$) 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 ($$p,3p$$) reaction is consistent with sequential proton collisions within the projectile nucleus.

論文

New excited 2$$^+$$ and 3$$^-$$ two-proton states in $$_{84}^{210}$$Po$$_{126}$$ populated by two-proton transfer

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

 被引用回数:0 パーセンタイル:100(Physics, Nuclear)

Five new 2$$^+$$ levels and one new 3$$^-$$ level were established in $$^{210}$$Po. The states were populated via the $$^{208}$$Pb($$^{12}$$C, $$^{10}$$Be) two-proton reaction experiment, performed at the JAEA Tandem in Tokai. A setup combining Ge, LaBr$$_3$$, and Si telescopes was used to detect in-beam $$gamma$$-rays and ejectile residues. Two-proton configurations were assigned to all new states. All assignments are strongly supported by shell-model calculations.

論文

Effects of the nuclear structure of fission fragments on the high-energy prompt fission $$gamma$$-ray spectrum in $$^{235}$$U($$n_{rm th},f$$)

牧井 宏之; 西尾 勝久; 廣瀬 健太郎; Orlandi, R.; L$'e$guillon, R.; 小川 達彦; Soldner, T.*; K$"o$ster, U.*; Pollitt, A.*; Hambsch, F.-J.*; et al.

Physical Review C, 100(4), p.044610_1 - 044610_7, 2019/10

 被引用回数:1 パーセンタイル:57.92(Physics, Nuclear)

The prompt fission $$gamma$$-ray energy spectrum for cold-neutron induced fission of $$^{235}$$U was measured in the energy range $$E_{rm gamma}$$ = 0.8 - 20,MeV, by gaining a factor of about 10$$^{5}$$ in statistics compared to the measurements performed so far. The spectrum exhibits local bump structures at $$E_{rm gamma}approx$$4,MeV and $$approx$$6,MeV, and also a broad one at $$approx$$15,MeV. In order to understand the origins of these bumps, the $$gamma$$-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 $$approx$$4,MeV is created by the transitions between the discrete levels in the fragments around $$^{132}$$Sn, and the bump at $$approx$$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 $$E_{rm gamma}approx$$15,MeV, induced by the transition feeding into the low-lying high-spin states.

論文

Study of medium-spin states of neutron-rich $$^{87,89,91}$$Rb isotopes

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

 被引用回数:0 パーセンタイル:100(Physics, Nuclear)

Excited states of the rubidium isotopes $$^{87,89,91}$$Rb were studied at the INFN Legnaro National Laboratory. Measurements of the $$gamma$$-ray of nuclei produced in binary reactions from the interaction of a beam of 530 MeV $$^{96}$$Zr ions with a $$^{124}$$Sn target were complemented by studies of the $$gamma$$-rays from nuclei produced in the interaction of a beam of 230 MeV $$^{36}$$S ions with a thick $$^{176}$$Yb target. The structure of the yrast states of $$^{87, 89, 91}$$Rb is discussed within the context of spherical shell-model and cranked Nilsson-Strutinsky calculations.

論文

Search for $$alpha$$ decay of $$^{104}$$Te with a novel recoil-decay scintillation detector

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

 被引用回数:4 パーセンタイル:14.53(Physics, Nuclear)

A search for super-allowed $$alpha$$ decay of N=Z nuclei $$^{104}$$Te and $$^{108}$$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 $$^{58}$$Ni+$$^{54}$$Fe$$rightarrow$$ $$^{112}$$Xe$$^*$$ were separated by the JAEA Recoil Mass Separator (RMS) and implanted into the YAP:Ce crystal. $$alpha$$ decays of neutron-deficient tellurium isotopes were identified and proton-emission of $$^{109}$$I was observed. No conclusive evidence was found for the decay chain $$^{108}$$Xe$$rightarrow$$$$^{104}$$Te$$rightarrow$$ $$^{100}$$Sn within 3 days experiment. The cross section limit of 130 pb was obtained for production of two events of $$^{108}$$Xe, about an order of magnitude below the expectation based on earlier cross section measurements and HIVAP calculations.

論文

Electromagnetic properties of low-lying states in neutron-deficient Hg isotopes; Coulomb excitation of $$^{182}$$Hg, $$^{184}$$Hg, $$^{186}$$Hg and $$^{188}$$Hg

Wrzosek-Lipska, K.*; Rezynkina, K.*; Bree, N.*; Zieli$'n$ska, 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

 被引用回数:5 パーセンタイル:14.53(Physics, Nuclear)

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 $$^{182-188}$$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$$^{+}_{1,2}$$, 2$$^{+}_{1,2}$$, and 4$$^{+}_{1}$$ states was observed in all nuclei under study. Reduced $$E2$$ 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.

論文

Inclusive cross sections for one- and multi-nucleon removal from Sn, Sb, and Te projectiles beyond the $$N$$ = 82 shell closure

Vaquero, V.*; Jungclaus, A.*; Rodr$'i$guez-S$'a$nchez, 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

 被引用回数:1 パーセンタイル:57.92(Astronomy & Astrophysics)

Inclusive one- and multi-nucleon removal cross sections were measured for several Sn, Sb and Te isotopes beyond the $$N$$ = 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 $$^{134}$$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.

論文

Validation of the multinucleon transfer method for the determination of the fission barrier height

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

 被引用回数:0 パーセンタイル:100(Physics, Nuclear)

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 $$^{18}$$O+$$^{237}$$Np reaction, fission barrier heights were inferred from fission probabilities of the nuclei $$^{239}$$Np and $$^{239,240}$$Pu produced in the $$2n$$ and $$pn/p2n$$ 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.

論文

Proton shell evolution below $$^{132}$$Sn; First measurement of low-lying $$beta$$-emitting isomers in $$^{123,125}$$Ag

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

 被引用回数:1 パーセンタイル:60.52(Physics, Multidisciplinary)

$$beta$$-delayed $$gamma$$-ray spectroscopy of the neutron-rich isotopes $$^{123,125}$$Ag was carried out at RIBF, RIKEN. The long predicted 1/2$$^{-}$$ $$beta$$ 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.

論文

New isomers in $$^{125}$$Pd$$_{79}$$ and $$^{127}$$Pd$$_{81}$$; Competing proton and neutron excitations in neutron-rich palladium nuclides towards the $$N=82$$ shell closure

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

 被引用回数:0 パーセンタイル:100(Astronomy & Astrophysics)

The isotopes $$^{125}$$Pd and $$^{127}$$Pd, respectively with 79 and 81 neutrons, are key isotopes to understand the evolution of the N=82 shell closure below $$^{208}$$Pd. These nuclei were studied at RIBF (RIKEN). New isomeric states with half-lives of 144(4) ns and 39(6) $$mu$$s were assigned spins and parities of (23/2$$^+$$) and (19/2$$^+$$) in $$^{125}$$Pd and $$^{127}$$Pd, respectively. The assignment was carried out based on the results of the $$gamma$$-ray intensity balance analysis and the measured transition strengths with the aid of a shell-model calculation. The isomoer in $$^{125}$$Pd was ascribed predominantly to three neutron-hole excitations in the N=50-82 shell. The 19/2$$^+$$ state in $$^{127}$$Pd is expected to involve the coupling of proton and neutron configurations. The new data will provide important benchmarks for a better understanding of $$r$$-process nucleosynthesis.

論文

Prominence of pairing in inclusive ($$p,2p$$) and ($$p,pn$$) cross sections from neutron-rich nuclei

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

 被引用回数:2 パーセンタイル:40.09(Physics, Multidisciplinary)

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.

論文

In-beam $$gamma$$-ray spectroscopy of $$^{136}$$Te at relativistic energies

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

 被引用回数:3 パーセンタイル:22.15(Physics, Nuclear)

The reduced transition probability B(E2; 0$$^+_1rightarrow 2^+_1$$) to the first excited 2$$^+$$ state of the neutron-rich nucleus $$^{136}$$Te, with two protons and two neutrons outside the doubly magic $$^{132}$$Sn core, was measured via Coulomb excitation at relativistic energies at the RIKEN Radioactive Isotope Beam Factory. In the experiment, $$^{136}$$Te isotopes impinged on a 950 mg/cm$$^2$$ Au target. The measured B(E2) value, 0.191(26) e$$^2$$b$$^2$$, 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.

論文

Observation of the competing fission modes in $$^{178}$$Pt

Tsekhanovich, I.*; Andreyev, A. N.; 西尾 勝久; Denis-Petit, D.*; 廣瀬 健太郎; 牧井 宏之; Matheson, Z.*; 森本 幸司*; 森田 浩介*; Nazarewicz, W.*; et al.

Physics Letters B, 790, p.583 - 588, 2019/03

 被引用回数:8 パーセンタイル:4.7(Astronomy & Astrophysics)

Fragment mass distributions from fission of the excited compound nucleus $$^{178}$$Pt have been deduced from the measured fragment velocities. The $$^{178}$$Pt nucleus was created at the JAEA tandem facility in a complete fusion reaction $$^{36}$$Ar+$$^{142}$$Nd, at beam energies of 155, 170 and 180 MeV. The data are indicative of a mixture of the mass-asymmetric and mass-symmetric fission modes associated with higher and lower total kinetic energies of the fragments, respectively. The measured fragment yields are dominated by asymmetric mass splits, with the symmetric mode contributing at the level of $$approx$$ 1/3. This constitutes the first observation of a multimodal fission in the sub-lead region. Most probable experimental fragment-mass split of the asymmetric mode, $$A_{rm L}$$/$$A_{rm H}$$ $$approx$$ 79/99, is well reproduced by nuclear density functional theory using the UNEDF1-HFB and D1S potentials. The symmetric mode is associated by theory with very elongated fission fragments, which is consistent with the observed total kinetic energy/fragment mass correlation.

論文

A New detector system for the measurement of high-energy prompt $$gamma$$-rays for low-energy neutron induced fission

牧井 宏之; 西尾 勝久; 廣瀬 健太郎; Orlandi, R.; L$'e$guillon, R.*; 小川 達彦; Soldner, T.*; Hambsch, F.-J.*; A$"i$che, M.*; Astier, A.*; et al.

Nuclear Instruments and Methods in Physics Research A, 906, p.88 - 96, 2018/10

 被引用回数:3 パーセンタイル:36.93(Instruments & Instrumentation)

中性子誘起核分裂における即発高エネルギー$$gamma$$線を観測するための新しい測定システムの開発を行った。測定システムは核分裂片を観測するための多芯線比例計数管と$$gamma$$線測定用のLaBr$$_{3}$$(Ce)シンチレータから構成される。開発したシステムを仏国ラウエ・ランジュバン研究所にある高中性子束炉のPF1Bコースに設置して、$$^{235}$$U中性子誘起核分裂における即発$$gamma$$線を行った。測定ではエネルギー最大20MeVまでの$$gamma$$線スペクトルの観測に成功し、$$^{235}$$U中性子誘起核分裂において非常に高いエネルギーの$$gamma$$線が放出されていることを確認した。

論文

Neutron-hole states in $$^{131}$$Sn and spin-orbit splitting in neutron-rich nuclei

Orlandi, R.; Pain, S. D.*; Ahn, S.*; Jungclaus, A.*; Schmitt, K. T.*; Bardayan, D. W.*; Catford, W. N.*; Chapman, R.*; Chipps, K. A.*; Cizewski, J. A.*; et al.

Physics Letters B, 785, p.615 - 620, 2018/10

 被引用回数:4 パーセンタイル:35.83(Astronomy & Astrophysics)

Low-lying neutron-hole states in $$^{131}$$Sn were populated via the $$^{132}$$Sn(d,t) reaction at Oak Ridge National Laboratory. The triton angular distributions were compared to DWBA calculations and revealed spectroscopic factors compatible with a single-hole nature of the states populated. The data permit to determine the spin-orbit splitting of the strongly bound $$d_{3/2}$$ and $$d_{5/2}$$ neutron orbits below the shell gap, which was compared to the splitting of the weakly bound 3$$p$$ and 2$$f$$ orbits above the gap. The comparison revealed a smaller energy splitting of the 3$$p$$ orbits. All splittings were reproduced using Woods-Saxon calculations, and the lower splitting of the 3$$p$$ orbits was explained to arise from the large radial extent of the wavefunction and small value of the amplitude at the surface. This result is important to understand at a fundamental level the spin-orbit interaction, and its effects on neutron-rich nuclei.

論文

Is seniority a partial dynamic symmetry in the first $$nu$$$$g_{9/2}$$ shell?

Morales, A. I.*; Orlandi, R.; 他61名*

Physics Letters B, 781, p.706 - 712, 2018/06

 被引用回数:9 パーセンタイル:13.16(Astronomy & Astrophysics)

By studying the $$beta$$ decay of the radioactive nuclei $$^{72}$$Co and $$^{74}$$Co produced at RIBF, RIKEN, the low-lying excited states in $$^{72,74}$$Ni were studied for the first time up to spin 8$$^+$$. These states originate from the valence neutrons occupying the $$g_{9/2}$$ orbit, and permit to investigate the seniority quantum number. The data reveal that the seniority isomerism of the 8$$^+$$ state disappears, and this phenomenon is explained by comparison with shell model calculations and the influence of spherical doubly-magic $$^{78}$$Ni.

論文

Quasiparticle phonon model description of low-energy states in $$^{152}$$Pr

Alexa, P.*; Ramdhane, M.*; Thiamova, G.*; Simpson, G. S.*; Faust, H. R.*; Genevey, J.*; K$"o$ster, U.*; Materna, T.*; Orlandi, R.; Pinston, J. A.*; et al.

Physical Review C, 97(3), p.034327_1 - 034327_6, 2018/03

 被引用回数:1 パーセンタイル:77.08(Physics, Nuclear)

Delayed $$gamma$$-ray and conversion-electron spectroscopy was performed on A = 152 fission fragments, at the Lohengrin spectrometer of the Institut Laue-Langevin, Grenoble, France. In this study, a new decay scheme was observed for the odd-odd nuclide $$^{158}$$Pr. The low-energy structure of this isotope was analysed by comparison with the quasiparticle phonon model and the particle-rotor model. The main configurations for the ($$3^+$$) ground state and for the 4.7(3)-$$mu$$s ($$1^+$$) isomer at 115 keV were assigned to, respectively, $$pi$$3/2[541]$$otimes$$$$nu$$3/2[521] and $$pi$$3/2[422]$$otimes$$$$nu$$5/2[642].

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

 被引用回数:26 パーセンタイル:7.66(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

Study of fission using multi-nucleon transfer reactions

西尾 勝久; 廣瀬 健太郎; Vermeulen, M. J.; 牧井 宏之; Orlandi, R.; 塚田 和明; 浅井 雅人; 豊嶋 厚史; 佐藤 哲也; 永目 諭一郎; et al.

EPJ Web of Conferences, 163, p.00041_1 - 00041_6, 2017/11

 被引用回数:1 パーセンタイル:100

We are promoting a study of fission using multi-nucleon transfer (MNT) reactions, where excited states in neutron-rich actinide nuclei, which cannot be accessed by particle capture and/or fusion reactions, are populated. Also, the excited states in the fissioning nucleus are widely populated by the MNT reactions, from which effects of excitation energy on fission properties can be investigated. Experiments were carried out at the JAEA tandem facility in Tokai, Japan. We studied reactions using the $$^{18}$$O beam and several actinide target nuclei such as $$^{232}$$Th, $$^{238}$$U, $$^{237}$$Np, $$^{248}$$Cm. Ejectile nucleus was identified by a silicon $$Delta$$E-E telescope to identify transfer channel and hence the compound nucleus. Fission fragments were detected by multi-wire proportional counters, and fission fragment mass distributions (FFMDs) were measured for each isotope. Measured FFMDs are reproduced by a calculation based on the fluctuation-dissipation model, and importance of multi-chance fission concept is investigated. Fission fragment angular distribution relative to the recoil direction suggested the increase of the spin of the fissioning nucleus with the number of transferred nucleons.

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