Neutron-Proton, Neutron-Neutron, Proton-Proton QRPA for the Gamow-Teller and the M1 Spin Transitions of N Z Nuclei in the s − d Shell

Abstract

We study the Gamow-Teller (GT) and the M1 spin transitions of thes - dshell nuclei(24)Mg,Mg-26,Si-28,S-32, and(36)Ar by using a quasiparticle random phase approximation (QRPA) scheme that comprises neutron-proton (np), neutron-neutron (nn) and proton-proton (pp) QRPA owing to the inclusion of thenppairing, as well asnnandpppairing correlations. At present, we work in spherical symmetry under the assumption that the deformations of the nuclei considered in this work are small enough to neglect, as was customary in past applications. For the GT transition, as well as single and double beta decays, the neutron-proton QRPA (npQRPA) is usually employed. For the M1 spin transition, theppandnnQRPA is needed due to its neutral current property. Thenppairing correlations couple thenpQRPA to thennandppQRPA. Therefore, the couplednp+nn+ppQRPA enables us to investigate simultaneously the GT and the M1 spin transitions. In particular, in this work, detailed analyses of particle-particle and particle-hole interactions at the QRPA stage are performed for the GT and the M1 spin transitions of the well-knowns - dshellN similar or equal to Znuclei, and the results are compared to available data. The roles of thenppairing correlations are also discussed for those transitions.