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論文

Coexisting normal and intruder configurations in $$^{32}$$Mg

北村 徳隆*; Wimmer, K.*; Poves, A.*; 清水 則孝*; Tostevin, J. A.*; Bader, V. M.*; Bancroft, C.*; Barofsky, D.*; Baugher, T.*; Bazin, D.*; et al.

Physics Letters B, 822, p.136682_1 - 136682_7, 2021/11

 被引用回数:0

ミシガン州立大学の国立超伝導サイクロトロン研究所にて、中性子過剰核$$^{32}$$Mgの励起状態を$$^{33}$$Mgからの1中性子ノックアウト反応および$$^{34}$$Siからの2陽子ノックアウト反応によって生成し、そこからの脱励起ガンマ線をGRETINA検出器を用いて観測した。$$^{32}$$Mgは中性子魔法数20が消失していることが古くから知られている原子核であるが、10年ほど前に理論予想よりもはるかに低い励起エネルギーに$$0^+_2$$状態が出現することがわかり、その核構造は完全には解明されていない。この実験で得られた生成断面積を理論計算と比較したところ、$$0^+_2$$状態の位置を再現する最近の理論計算で予言される、励起エネルギー2MeV以下の大きな断面積は実験では得られず、$$0^+_2$$状態の位置を再現しない古い理論計算に近い断面積分布となることがわかった。この結果から、$$^{32}$$Mgの低い$$0^+_2$$状態の謎は未だに残されたままとなった。

論文

Structure of $$^{30}$$Mg explored via in-beam $$gamma$$-ray spectroscopy

北村 徳隆*; Wimmer, K.*; 清水 則孝*; Bader, V. M.*; Bancroft, C.*; Barofsky, D.*; Baugher, T.*; Bazin, D.*; Berryman, J. S.*; Bildstein, V.*; et al.

Physical Review C, 102(5), p.054318_1 - 054318_13, 2020/11

 被引用回数:1 パーセンタイル:0.02(Physics, Nuclear)

$$^{30}$$Mgは中性子数20の魔法数が消滅する原子核としてよく知られている$$^{32}$$Mgの2中性子少ない系であり、魔法数消滅のメカニズムを解明する重要な情報を与える原子核である。この研究では、ミシガン州立大学のサイクロトロンを用いて$$^{31}$$Mgからの中性子ノックアウト反応によって$$^{30}$$Mgを生成し、そのガンマ線分光から構造を探求した。変形の小さなバンドと変形の大きなバンドの他に負パリティ状態と見られるエネルギー準位が得られ、それらの分光学的因子が導かれた。その結果を大規模殻模型計算と比較したところ、エネルギー準位はよく再現するものの、分光学的因子の一部に不一致があり、より正確な記述という観点からは理論に課題があることがわかった。

論文

Spectroscopy of $$^{46}$$Ar by the ($$t,p$$) two-neutron transfer reaction

Nowak, K.*; Wimmer, K.*; Hellgartner, S.*; M$"u$cher, D.*; Bildstein, V.*; Diriken, J.*; Elseviers, J.*; Gaffney, L. P.*; Gernh$"a$user, R.*; Iwanicki, J.*; et al.

Physical Review C, 93(4), p.044335_1 - 044335_10, 2016/04

 被引用回数:11 パーセンタイル:71(Physics, Nuclear)

The $$^{44}$$Ar($$t,p$$)$$^{46}$$Ar two-neutron transfer reaction at 2.16 MeV/u was studied at CERN using a $$^{44}$$Ar radioactive beam and a tritium loaded radioactive target. Angular distributions for three final states were measured and based on the shape of the differential cross section an excited state at 3695 keV was identified as the first excited 0$$+$$ state. The differential cross-sections for the 0$$^+$$-ground state, and first excited 2$$^+$$ and 0$$^+$$ states are compared to DWBA calculations including two-step reactions through the intermediate nucleus $$^{45}$$Ar. By comparison large scale shell model calculations using state-of-the-art effective interactions, with and without the tensor components of the interactions, it was observed that the cross-shell proton-neutron tensor interaction has measurable effects on the observables at low excitation energy in $$^{46}$$Ar.

論文

Experimental study of the $$^{66}$$Ni($$d$$,$$p$$)$$^{67}$$Ni one-neutron transfer reaction

Diriken, J.*; Patronis, N.*; Andreyev, A.; Antalic, S.*; Bildstein, V.*; Blazhev, A.*; Darby, I. G.*; De Witte, H.*; Eberth, J.*; Elseviers, J.*; et al.

Physical Review C, 91(5), p.054321_1 - 054321_15, 2015/05

 被引用回数:8 パーセンタイル:57.47(Physics, Nuclear)

Excited states up to an excitation energy of 5.8 MeV were populated in the neutron-rich isotope $$^{67}$$Ni via the $$^{66}$$Ni(d,p) transfer reaction at REX-Isolde, CERN. In particular, single-neutron states above the N=40 sub-shell gap were populated, and the relative spectroscopic factors were extracted using distorted-wave Born approximation analysis. The positive parity g$$_{9/2}$$, d$$_{5/2}$$ and s$$_{1/2}$$ neutron orbits above the shell closure are assumed to induce strong quadrupole collectivity in neutron-rich Fe and Cr isotopes. The extracted relative spectroscopic factors show that the strength of the d$$_{5/2}$$ orbit is mostly split over two states, hinting to substantial mixing of the neutron d$$_{5/2}$$ configuration with collective modes of the core. The size of the N=50 shell gap was also estimated, and found to be 2.6 MeV near $$^{68}$$Ni, as also determined in lighter Ni isotopes.

論文

Single-neutron orbits near $$^{78}$$Ni; Spectroscopy of the N=49 isotope $$^{79}$$Zn

Orlandi, R.; M$"u$cher, D.*; Raabe, R.*; Jungclaus, A.*; Pain, S. D.*; Bildstein, V.*; Chapman, R.*; De Angelis, G.*; Johansen, J. G.*; Van Duppen, P.*; et al.

Physics Letters B, 740, p.298 - 302, 2015/01

 被引用回数:20 パーセンタイル:82.78(Astronomy & Astrophysics)

Single-neutron states in $$^{79}$$Zn have been populated using the reaction $$^{78}$$Zn(d,p) at REX-Isolde, CERN. The analysis reveals that the lowest excited states in $$^{79}$$Zn lie at approximately 1 MeV, and involve neutron orbits above the N=50 shell gap. A 5/2$$^{+}$$ configuration was assigned to the 983-keV state. Comparison with large-scale shell model calculations supports a robust neutron N=50 shell closure for $$^{78}$$Ni. These data constitute an important step towards the understanding the magicity of $$^{78}$$Ni and the structure of nuclei in the region.

論文

Study of the deformation-driving $$nu$$d$$_{5/2}$$ orbital in $$_{28}^{67}$$Ni$$_{39}$$ using one-neutron transfer reactions

Diriken, J.*; Patronis, N.*; Andreyev, A. N.*; Antalic, S.*; Bildstein, V.*; Blazhev, A.*; Darby, I. G.*; De Witte, H.*; Eberth, J.*; Elseviers, J.*; et al.

Physics Letters B, 736, p.533 - 538, 2014/09

 被引用回数:17 パーセンタイル:75.99(Astronomy & Astrophysics)

The neutron orbits $$g_{9/2}$$, d$$_{5/2}$$ and s$$_{1/2}$$ are assumed to be responsible for the swift onset of collectivity observed in the region below $$^{68}$$Ni. In order to gather information on the single-particle energies and spectroscopic factors of these orbitals, single-particle states in the nucleus $$^{67}$$Ni were populated using the reaction $$^{66}$$Ni(d,p), in inverse kinematics, at REX-ISOLDE, CERN. The new isotope was studied using combined particle-$$gamma$$ spectroscopy. Comparison with DWBA calculations, permitted the identification of positive parity states with a substantial amount of $$nu$$d$$_{9/2}$$ (1007 keV) and $$nu$$d$$_{5/2}$$ (2207 and 3277 keV) single-particle strength. Comparisons with extended Shell-Model calculations was also performed to confirm the single-particle nature of these states, and to deduce general properties around $$^{68}$$Ni.

口頭

Low-energy states in $$^{79}$$Zn and the structure of $$^{78}$$Ni

Orlandi, R.; M$"u$cher, D.*; Raabe, R.*; Jungclaus, A.*; Pain, S. D.*; Bildstein, V.*; Chapman, R.*; De Angelis, G.*; Johansen, J. G.*; Van Duppen, P.*; et al.

no journal, , 

Single-neutron states in the $$N$$ = 49 isotope $$^{79}$$Zn were populated in the $$^{78}$$Zn(d,p)$$^{79}$$Zn transfer reaction at REX-ISOLDE, CERN. The combined detection of protons ejected in the reaction and of $$gamma$$ rays emitted by $$^{79}$$Zn permitted the identification of the lowest-lying 5/2$$^+$$ and 1/2$$^+$$ excited states. The analysis of proton angular distributions links these states to a significant amount of single-particle strength around 1 MeV, and specifically to the $$nu$$d$$_{5/2}$$ and $$nu$$s$$_{1/2}$$ neutron orbits, which lie above the $$N$$ = 50 neutron shell gap. Comparison with large-scale-shell-model calculations supports a robust $$N$$ = 50 shell-closure for $$^{78}$$Ni. These data constitute a considerable step towards the understanding of the magicity of $$^{78}$$Ni and of the structure of isotopes in the region.

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