Properties of isocalar-pair condensates

It is pointed out that the ground state of n neutrons and n protons in a single-j shell, interacting through an isoscalar (T=0) pairing force, is not paired, J=0, but rather spin-aligned, J=n. This observation is explained in the context of a model of isoscalar P (J=1) pairs, which is mapped onto a system of p bosons, leading to an approximate analytic solution of the isoscalar-pairing limit in jj coupling.Comment: 7 pages, 3 figures, 1 tabl

Shell model analysis of the B(E2, 2+ → 0+) values in the A = 70, T = 1 triplet 70Kr, 70Br, and 70Se

The B(E2, 2+ → 0+) transition strengths of the T = 1 isobaric triplet 70Kr, 70Br, 70Se, recently measured at the RIKEN Radioactive Isotope Beam Factory (RIBF), are discussed in terms of state-of-the-art large scale shell model calculations using the JUN45 and JUN45+LNPS plus Coulomb interactions. In this Letter we argue that, depending on the effective charges used, the calculations are either in line with the experimental data within statistical uncertainties, or the anomaly happens in 70Br, rather than 70Kr. In the latter case, we suggest that it can be due to the presence of a hitherto undetected 1+ T = 0 state below the yrast 2+ T = 1 state. Our results do not support a shape change of 70Kr with respect to the other members of the isobaric multiple

Microscopic structure of fundamental excitations in N=Z nuclei

Excitation energies of the $T$=1 states in even-even as well as $T$=0 and $T$=1 states in odd-odd $N$=$Z$ nuclei are calculated within the mean-field approach. It is shown that the underlying structure of these states can be determined in a consistent manner only when both isoscalar and isovector pairing collectivity as well as isospin projection, treated within the iso-cranking approximation, are taken into account. In particular, in odd-odd $N$=$Z$ nuclei, the interplay between quasiparticle excitations (relevant for the case of $T$=0 states) and iso-rotations (relevant for the case of $T$=1 states) explains the near-degeneracy of these fundamental excitations.Comment: 4 pages, 4 figure