Nuclear structure far off stability --Implications for nuclear astrophysics

Abstract

Abstract. The single-particle structure and shell gap of 100 Sn as inferred from previous in-beam γ-ray spectroscopy has been confirmed in recent studies of seniority and spin-gap isomers by γγ, βγ, βpγ, pγ and 2pγ spectroscopy. The results for 94,95 Ag, 98 Cd and its N = 50 isotones 96 Pd and 94 Ru stress the importance of large-scale shell model calculations employing realistic interactions for the isomerism, np-nh excitations, seniority mixing and E2 polarisation of the 100 Sn core. The strong monopole interaction of the ∆l = 0, 1 spin/isospin-flip partners πg 9/2 -νg 7/2 along the N = 50 isotones and the πf 5/2 -νg 9/2 pair of nucleons along the Z = 28 Ni isotopes are decisive for the evolution of the shell structure towards 100 Sn and 78 Ni. It can be traced back to the tensor force in the effective nucleon-nucleon interaction and provides a straightforward explanation for new shells in neutron-rich light nuclei, implying qualitative predictions for new N = 32, 34 subshells in Ca isotopes, persistence of the 78 Ni proton and neutron shell gaps and non-equivalence of the g 9/2 valence mirror Ni isotopes and N = 50 isotones. This is corroborated by recent experimental data on 56,58 Cr and 70-76 Ni. The implication of monopole driven shell evolution for apparent spin-orbit splitting towards N Z and structure along the astrophysical r-path between N = 50 and N = 82 is discussed.

New sub-μs isomers in125,127,129Snand isomer systematics ofLozeva1, Simpson2, Grawe3 et al. 2008Phys. Rev. CSelf Cite

“…IV A, the weak B(E2) values in the h 11/2 mid-shell are specifically sensitive to the neglect of proton-core excitations. This was demonstrated in the N = 50 isotones one major 064313-12 shell below for g 9/2 protons [15,58]. Further SM tests of the h −n 11/2 B(E2) have revealed that the underestimation of the 125,126 Sn values can be cured by reducing the pairing two-body matrix elements (TBME) involving h 11/2 , while the B(E2) for the other configurations are virtually unchanged.…”

High-spin isomers in96Ag: Excitations across theZ=38andZ=50,Boutachkov1, Górska2, Grawe3 et al. 2011Phys. Rev. CSelf Cite249370View full textAdd to dashboardCite

“…There are many isomeric states predicted and observed near the doubly magic 100 Sn nucleus [1,2]. Their existence and properties are governed by the strong proton-neutron (πν) interaction between identical orbitals, and in particular the high-spin πg 9/2 and νg 9/2 orbits.…”

Observation of a new high-spin isomer inPd94

“…The region is generally well described by the SM in a minimum space comprising p 1/2 and g 9/2 protons and neutrons [3][4][5]. Exploration of the limits of this approach with respect to inclusion of the p 3/2 and f 5/2 orbitals and excitations across the N = Z = 50 shell closure is a challenge both to the SM and experimental techniques.This region is also remarkable for an abundance of isomeric states [6]. Particularly interesting is the occurrence of high-spin isomers which can provide an ideal testing ground for the study of neutron-proton interactions near the N = Z line [6].…”

“…This region is also remarkable for an abundance of isomeric states [6]. Particularly interesting is the occurrence of high-spin isomers which can provide an ideal testing ground for the study of neutron-proton interactions near the N = Z line [6].…”

“…Particularly interesting is the occurrence of high-spin isomers which can provide an ideal testing ground for the study of neutron-proton interactions near the N = Z line [6]. One of the most striking cases is the (21 + ) level in 94 Ag, with recent papers reporting evidence for a variety of particle decay channels: β [7,8], βp [9], p [10], and 2p [11].…”