TEMPERATURE-DEPENDENCE OF PAIR CORRELATIONS IN NUCLEI IN THE IRON REGION

We use the shell-model Monte Carlo approach to study thermal propertie s and pair correlations in Fe-54,Fe-56,Fe-58 and in Cr-56, The calcula tions are performed with the modified Kuo-Brown interaction in the com plete 1p0f model space. We find generally that the proton-proton and n eutron-neutron J = 0 pairing correlations, which dominate the ground-s tate properties of even-even nuclei, vanish at temperatures around 1 M eV, This pairing phase transition is accompanied by a rapid increase i n the moment of inertia and a partial unquenching of the M1 strength, We find that the M1 strength totally unquenches at higher temperatures , related to the vanishing of isoscalar proton-neutron correlations, w hich persist to higher temperatures than the pairing between like nucl eons. The Gamow-Teller strength is also correlated to the isoscalar pr oton-neutron pairing and hence also unquenches at a temperature larger than that of the pairing phase transition.