Proton-neutron pairing in Z=N nuclei with A=76-96 -: art. no. 014311

The ground states of even-even Z = N nuclei are determined with the isospin generalized BCS equations and the HFB equation. The calculations permit the simultaneous existence of the following Cooper pairs: pp, nn, pn(T = 1), and pn(T = 0) where the two nucleons in a pair occupy space-spin orbitals which are related by time reversal, as well as pn(T = 0) where the two nucleons are in identical space-spin orbitals. There is a transition from T = 1 Cooper pairs at the beginning of this isotope sequence to T = 0 Cooper pairs at the end of the sequence. Near the middle of the isotope sequence, there is coexistence of a T = 0 pair superfluid and a T = 1 pair superfluid in the same wave function. The fluctuation in the particle number is reduced if the wave function contains proton-neutron pairing. The fluctuation in the isospin is eliminated and isospin is conserved if the wave function contains only T = 0 pairing.