[paper] Interplay between nuclear shell evolution and shape deformation revealed by the magnetic moment of 75Cu

Interplay between nuclear shell evolution and shape deformation revealed by the magnetic moment of 75Cu

Y. Ishikawa et al.
Nature Physics (2019)
DOI: 10.1038/s41567-018-0410-7

Exotic nuclei are characterized by having a number of neutrons (or protons) in excess relative to stable nuclei. Their shell structure, which represents single-particle motion in a nucleus, may vary due to nuclear force and excess neutrons, in a phenomenon called shell evolution. This effect could be counterbalanced by collective modes causing deformations of the nuclear surface. Here, we study the interplay between shell evolution and shape deformation by focusing on the magnetic moment of an isomeric state of the neutron-rich nucleus 75Cu. We measure the magnetic moment using highly spin-controlled rare-isotope beams and achieve large spin alignment via a two-step reaction scheme that incorporates an angular-momentum-selecting nucleon removal. By combining our experiments with numerical simulations of many-fermion correlations, we find that the low-lying states in 75Cu are, to a large extent, of single-particle nature on top of a correlated 74Ni core. We elucidate the crucial role of shell evolution even in the presence of the collective mode, and within the same framework we consider whether and how the double magicity of the 78Ni nucleus is restored, which is also of keen interest from the perspective of nucleosynthesis in explosive stellar processes.

[paper] Nuclear processes in astrophysics: Recent progress

Nuclear processes in astrophysics: Recent progress

by V. Licciardo et al.
doi: 10.1140/epja/i2018-12648-5

The question about the origin of the elements is a fascinating one, that scientists have been trying to answer for the last seven decades. The formation of light elements in the primordial universe and heavier elements in astrophysical sources occurs through nuclear reactions. We can say that nuclear processes are responsible for the production of energy and synthesis of elements in the various astrophysical sites. Thus, nuclear reactions have a determining role in the existence and evolution of several astrophysical environments, from the Sun to the spectacular explosions of supernovae. Nuclear astrophysics attempts to address the most basic and important questions of our existence and future. There are still many issues that are unresolved, such as how stars and our Galaxy have formed and how they evolve, how and where the heaviest elements are made, what is the abundance of nuclei in the universe and what is the nucleosynthesis output of the various production processes and why the amount of lithium-7 observed is less than predicted. In this paper, we review our current understanding of the different astrophysical nuclear processes leading to the formation of chemical elements and pay particular attention to the formation of heavy elements occurring during high-energy astrophysical events. Thanks to the recent multi-messenger observation of a binary neutron star merger, which also confirmed production of heavy elements, explosive scenarios such as short gamma-ray bursts and the following kilonovae are now strongly supported as nucleosynthesis sites.

 

[paper] Isoscalar Spin Matrix Elements in s–d Shell Nuclei

Isoscalar Spin Matrix Elements in s–d Shell Nuclei

by Akito Arima and Wolfgang Bentz

doi: 10.7566/JPSCP.23.012011

The quenching of isovector spin matrix elements in s–d shell nuclei is well established experimentally as well as theoretically [1,2,3]. The isoscalar spin gyromagnetic ratios gsIS of nuclei with one nucleon or hole outside of LS closed shells are also quenched by the same mechanism. On the other hand, their isoscalar orbital gyromagnetic ratios gLIS are slightly enhanced by meson exchange currents [1,2]. Then we are interested very much in the following question: Are the isoscalar spin matrix elements generally quenched in s–d shell nuclei? We will try to answer this question in this paper.