Different particle alignments in N \approx Z Ru isotopes studied by the shell model

Abstract

Experimentally observed heaviest $N\approx Z$ nuclei, Ru isotopes, are investigated by the shell model on a spherical basis with the extended $P+QQ$ Hamiltonian. The energy levels of all the Ru isotopes can be explained by the shell model with a single set of force parameters. The calculations indicate enhancement of quadrupole correlations in the $N=Z$ nucleus ${}^{88}$Ru as compared with the other Ru isotopes, but the observed moments of inertia seem to require much more enhancement of quadrupole correlations in ${}^{88}$Ru. It is discussed that the particle alignment takes place at $8^{+}$ in ${}^{90}$Ru but is delayed in ${}^{88}$Ru till $16^{+}$ where the simultaneous alignments of proton and neutron pairs take place. The calculations present interesting predictions for ${}^{89}$Ru that the ground state is the $1/2^{-}$ state and there are three $\Delta J=2$ bands with different particle alignments including the T=0 $p-n$ pair alignment.

11 pages including 10 figures, to be published in Phys. Rev. C