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論文

Competition between allowed and first-forbidden $$beta$$ decays of $$^{208}$$At and expansion of the $$^{208}$$Po level scheme

Brunet, M.*; Podoly$'a$k, Zs.*; Berry, T. A.*; Brown, B. A.*; Carroll, R. J.*; Lica, R.*; Sotty, Ch.*; Andreyev, A. N.; Borge, M. J. G.*; Cubiss, J. G.*; et al.

Physical Review C, 103(5), p.054327_1 - 054327_13, 2021/05

https://doi.org/10.1103/PhysRevC.103.054327
 被引用回数：4 パーセンタイル：57.13(Physics, Nuclear)

The structure of $$^{208}$$Po populated through the EC/$$beta^{+}$$ decay of $$^{208}$$At is investigated using $$gamma$$-ray spectroscopy at the ISOLDE Decay Station. The presented level scheme contains 27 new excited states and 43 new transitions, as well as a further 50 previously observed $$gamma$$ rays which have been (re)assigned a position. Through the analysis using the shell model calculations approximately half of the $$beta$$-decay strength of $$^{208}$$At is found to proceed via allowed decay and half via first-forbidden decay. The first-forbidden transitions predominantly populate core excited states at high excitation energies, which is qualitatively understood using shell model considerations.

論文

Shell structure of the neutron-rich isotopes $$^{69,71,73}$$Co

Lokotko, T.*; Leblond, S.*; Lee, J.*; Doornenbal, P.*; Obertelli, A.*; Poves, A.*; Nowacki, F.*; 緒方 一介*; 吉田 数貴; Authelet, G.*; et al.

Physical Review C, 101(3), p.034314_1 - 034314_7, 2020/03

https://doi.org/10.1103/PhysRevC.101.034314
 被引用回数：10 パーセンタイル：69.78(Physics, Nuclear)

中性子過剰核である$$^{69,71,73}$$Coに対する($$p,2p$$)ノックアウト反応が理化学研究所RIBFで測定された。$$gamma-gamma$$ coincidenceの方法で準位構造が決定され、測定された包括的断面積および排他的断面積から暫定的ではあるがスピン・パリティが決定された。殻模型計算との比較により、$$^{69,71,73}$$Coの低励起状態には球形核と変形核が共存することが示唆された。

論文

Investigation of the $$Delta$$$$n$$ = 0 selection rule in Gamow-Teller transitions; The $$beta$$-decay of $$^{207}$$Hg

Berry, T. A.*; Podoly$'a$k, Zs.*; Carroll, R. J.*; Lic$u{a}$, R.*; Grawe, H.*; Timofeyuk, N. K.*; Alexander, T.*; Andreyev, A. N.; Ansari, S.*; Borge, M. J. G.*; et al.

Physics Letters B, 793, p.271 - 275, 2019/06

https://doi.org/10.1016/j.physletb.2019.04.039
 被引用回数：5 パーセンタイル：47.88(Astronomy & Astrophysics)

Gamow-Teller $$beta$$ decay is forbidden if the number of nodes in the radial wave functions of the initial and final states is different. This $$Delta$$$$n$$ = 0 requirement plays a major role in the $$beta$$ decay of heavy neutron-rich nuclei, affecting the nucleosynthesis through the increased half-lives of nuclei on the astrophysical $$r$$-process pathway below both $$Z$$ = 50 (for $$N >$$ 82) and $$Z$$ = 82 (for $$N >$$ 126). The level of forbiddenness of the $$Delta$$$$n$$ = 1 $$nu$$1$$g_{9/2} rightarrow pi$$0$$g_{7/2}$$ transition has been investigated from the $$beta^{-}$$ decay of the ground state of $$^{207}$$Hg into the single-proton-hole nucleus $$^{207}$$Tl in an experiment at the ISOLDE Decay Station. From statistical observational limits on possible $$gamma$$-ray transitions depopulating the $$pi$$0$$g^{-1}_{7/2}$$ state in $$^{207}$$Tl, an upper limit of 3.9$$times$$10$$^{-3}$$ % was obtained for the probability of this decay, corresponding to log$$ft >$$ 8.8 within a 95% confidence limit. This is the most stringent test of the $$Delta$$$$n$$ = 0 selection rule to date.

論文

Nuclear structure of $$^{76}$$Ni from the ($$p$$,$$2p$$) reaction

Elekes, Z.*; Kripk$'o$, $'A$*; Sohler, D.*; Sieja, K.*; 緒方 一介*; 吉田 数貴; Doornenbal, P.*; Obertelli, A.*; Authelet, G.*; 馬場 秀忠*; et al.

Physical Review C, 99(1), p.014312_1 - 014312_7, 2019/01

https://doi.org/10.1103/PhysRevC.99.014312
 被引用回数：10 パーセンタイル：64.15(Physics, Nuclear)

($$p$$,$$2p$$)反応による$$^{76}$$Niの核構造の探索実験を行った。Lenzi, Nowacki, Poves, Sieja相互作用を用いた殻模型計算では実験結果を説明しうる陽子空孔状態が得られており、理論的な断面積計算は実験値とよい一致を与えた。実験で得られたすべての状態を理論的に一意に決定することはできなかったが、過去の実験結果と同様にNi同位体でのZ = 28の大きなshell gapを示す結果が得られた。

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

https://doi.org/10.1016/j.physletb.2018.08.005
 被引用回数：7 パーセンタイル：53.6(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

Shell evolution beyond $$Z$$=28 and $$N$$=50; Spectroscopy of $$^{81,82,83,84}$$Zn

Shand, C. M.*; Podoly$'a$k, Zs.*; G$'o$rska, M.*; Doornenbal, P.*; Obertelli, A.*; Nowacki, F.*; Otsuka, T.*; Sieja, K.*; Tostevin, J. A.*; Tsunoda, T.*; et al.

Physics Letters B, 773, p.492 - 497, 2017/10

https://doi.org/10.1016/j.physletb.2017.09.001
 被引用回数：25 パーセンタイル：87.36(Astronomy & Astrophysics)

Low-lying states in neutron-rich $$^{81,82.83.84}$$Zn nuclei were measured for the first time via in-beam $$gamma$$-ray spectroscopy at RIKEN. These include the 4$$_1^+$$ to 2$$_1^+$$ in $$^{82}$$Zn and the 2$$_1^+$$ to 0$$_1^+$$ and 4$$_1^+$$ to 2$$_1^+$$ in $$^{84}$$Zn. The reduced E($$2^+$$) energies and increased E(4$$^+$$)/E(2$$^+$$) ratios at $$N$$=52,54 compared to $$^{80}$$Zn attest that the magicity is confined just on the neutron number $$N$$=50 only. The levels observed in $$^{84}$$Zn suggest the onset of deformation towards heavier Zn isotopes. The data were compared to state-of-the-art shell model calculations.

論文

Shape evolution in neutron-rich krypton isotopes beyond N=60; First spectroscopy of $$^{98,100}$$Kr

Flavigny, F.*; Doornenbal, P.*; Obertelli, A.*; Delaroche, J.-P.*; Girod, M.*; Libert, J.*; Rodriguez, T. R.*; Authelet, G.*; 馬場 秀忠*; Calvet, D.*; et al.

Physical Review Letters, 118(24), p.242501_1 - 242501_6, 2017/06

https://doi.org/10.1103/PhysRevLett.118.242501
 被引用回数：38 パーセンタイル：86.73(Physics, Multidisciplinary)

The first $$gamma$$-ray spectroscopy of very neutron rich $$^{98,100}$$Kr isotopes was carried out at the RIBF at RIKEN Nishina center. Excited states in these isotopes were populated via (p,2p) reactions using radioactive $$^{99,101}$$Rb beams accelerated to 220 MeV/nucleon. The new data show a significant increase in deformation beyond N=60, as well as competing configurations (shape-coexistence) at low energy. The data were compared with beyond-mean-field calculations which predict level energies in good agreement with observation, and suggest oblate-prolate shape coexistence.

論文

Low-lying structure and shape evolution in neutron-rich Se isotopes

Chen, S.*; Doornenbal, P.*; Obertelli, A.*; Rodriguez, T. R.*; Authelet, G.*; 馬場 秀忠*; Calvet, D.*; Ch$^a$teau, F.*; Corsi, A.*; Delbart, A.*; et al.

Physical Review C, 95(4), p.041302_1 - 041302_6, 2017/04

https://doi.org/10.1103/PhysRevC.95.041302
 被引用回数：26 パーセンタイル：88.02(Physics, Nuclear)

Neutron-rich isotopes of selenium, $$^{88,90,92,94}$$Se, where studied via in beam $$gamma$$-ray spectroscopy after nucleon removal reactions at RIBF in RIKEN. The low-energy excitations of these nuclei were investigated using $$gamma$$-$$gamma$$ coincidences, and the first and second excited 2$$^+$$ states were found at remarkably low energies. The analysis and comparison with self-consistent beyond-mean field calculations suggest that both shape coexistence and triaxiality are needed to describe these isotopes.

論文

Are there signatures of harmonic oscillator shells far from stability?; First spectroscopy of $$^{110}$$Zr

Paul, N.*; Corsi, A.*; Obertelli, A.*; Doornenbal, P.*; Authelet, G.*; 馬場 秀忠*; Bally, B.*; Bender, M.*; Calvet, D.*; Ch$^a$teau, F.*; et al.

Physical Review Letters, 118(3), p.032501_1 - 032501_7, 2017/01

https://doi.org/10.1103/PhysRevLett.118.032501
 被引用回数：43 パーセンタイル：88.64(Physics, Multidisciplinary)

The first measurement of $$gamma$$ rays emitted by the very neutron rich nuclei $$^{112}$$Mo (Z=42) and $$^{110}$$Zr (Z=40) was carried out at the RIBF facility at RIKEN. These data shine light on the postulated N=70 harmonic oscillator shell. If the spin-orbit splitting which gives rise to the N=82 shell gap is reduced in very neutron-rich nuclei, the harmonic oscillator gap at N=70 should open instead. However, both the measured energy of the first excited state $$^{112}$$Mo and $$^{110}$$Zr, respectively 235(7) keV and 185(11) keV, and their E(4$$^+$$)/E(2$$^+$$) ratio, indicate that these nuclei are good rotors, and exclude the shell stabilization scenario at Z=40 and N=70. These results were compared to state-of-the-art density functional theoretical calculations using Gogny and Skyrme effective interactions.

口頭

Neutron hole states in $$^{131}$$Sn studied via the $$^{132}$$Sn(d,t)$$^{131}$$Sn reaction

Orlandi, R.; Pain, S. D.*; Bardayan, D. W.*; Gross, C. J.*; Smith, M. S.*; Jungclaus, A.*; Ahn, S.*; Jones, K. L.*; Pittman, S. T.*; Schmitt, K. T.*; et al.

no journal, , 

Knowledge of single-particle energies in the vicinity of exotic doubly-magic nuclei is of critical importance to understand evolution of nuclear structure. In the present work, the $$^{132}$$Sn(d,t)$$^{131}$$Sn reaction (Q=-1.055 MeV) was studied in inverse kinematics at HRIBF of Oak Ridge National Laboratory. The $$^{132}$$Sn ISOL beam was post-accelerated to an energy of 4.39 MeV/u using the ORNL HRIBF accelerator. The beam (average intensity of $$sim$$1.2e4 pps) impinged on a $$sim$$250 $$mu$$g/cm$$^{2}$$ deuterated polyethylene target, for approximately 4 days. Ejected tritons were detected using the Super ORRUBA array of segmented Si telescopes. Low-lying states in $$^{131}$$Sn were populated in the experiment. Preliminary results will be shown.

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