PAIRING CORRELATIONS IN N-SIMILAR-TO-Z PF-SHELL NUCLEI

We perform Shell Model Monte Carlo calculations to study pair correlat ions in the ground states of N = Z nuclei with masses A = 48-60. We fi nd that T = 1, J(pi) = 0(+) proton-neutron correlations play an import ant, and even dominant role, in the ground states of odd-odd N = Z nuc lei, in agreement with experiment. By studying pairing in the ground s tales of Fe-52-58, we observe that the isovector proton-neutron correl ations decrease rapidly with increasing neutron excess. In contrast, b oth the proton, and trivially the neutron correlations increase as neu trons are added, We also study the thermal properties and the temperat ure dependence of pair correlations for Mn-50 and Fe-52 as exemplars o f odd-odd and even-even N = Z nuclei. While for Fe-52 results are simi lar to those obtained for other even-even nuclei in this mass range, t he properties of Mn-50 at low temperatures are strongly influenced by isovector neutron-proton pairing. In coexistence with these isovector pair correlations, our calculations also indicate an excess of isoscal ar proton-neutron pairing over the mean-field values. The isovector ne utron-proton correlations rapidly decrease with temperatures and vanis h for temperatures above T = 700 keV, while the isovector correlations among like-nucleons persist to higher temperatures. Related to the qu enching of the isovector proton-neutron correlations, the average isos pin decreases from 1, appropriate for the ground state, to 0 as the te mperature increases.