Is seniority a partial dynamic symmetry in the first vg(9/2) shell?


MORALES A. I. , BENZONI G., WATANABE H., DE ANGELIS G., NISHIMURA S., CORAGGIO L., ...More

PHYSICS LETTERS B, vol.781, pp.706-712, 2018 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 781
  • Publication Date: 2018
  • Doi Number: 10.1016/j.physletb.2018.04.049
  • Title of Journal : PHYSICS LETTERS B
  • Page Numbers: pp.706-712

Abstract

The low-lying structures of the midshell vg(9/2) Ni isotopes Ni-72 and Ni-74 have been investigated at the RIBF facility in RIKEN within the EURICA collaboration. Previously unobserved low-lying states were accessed for the first time following beta decay of the mother nuclei Co-72 and Co-74. As a result, we provide a complete picture in terms of the seniority scheme up to the first (8(+)) levels for both nuclei. The experimental results are compared to shell-model calculations in order to define to what extent the seniority quantum number is preserved in the first neutron g(9/2) shell. We find that the disappearance of the seniority isomerism in the (8(1)(+)) states can be explained by a lowering of the seniority-four (6(+)) levels as predicted years ago. For Ni-74, the internal de-excitation pattern of the newly observed (6(2)(+)) state supports a restoration of the normal seniority ordering up to spin J = 4. This property, unexplained by the shell-model calculations, is in agreement with a dominance of the single-particle spherical regime near Ni-78. (C) 2018 The Authors. Published by Elsevier B.V.