Lifetime measurements in Pt and Tl isotopes populated via multinucleon transfer reactions

Various Pt and Tl isotopes in the transitional region, which lie just below the heaviest doubly magic nucleus ²⁰⁸Pb (Z = 82 and N = 126), have been studied using the Gammasphere and INGA detector arrays. Lifetimes ranging from few nanoseconds to hundreds of microseconds have been identified in these nuclei. The structure of Pt isotopes (Z = 78) exhibits coexistence between oblate, triaxial and prolate shapes, and there is found to be a complex interplay between intrinsic and collective degrees of freedom. Rotation-aligned isomeric states and oblate collective sequences have been established across Pt isotopes up to I = 26ħ with respect to their ground states, relatively high for this region, with previous information limited to the I ~ 10-20 ħ range. Reduced E2 transition probabilities for the 12⁺ isomeric states in even-A Pt isotopes indicate an abrupt reduction in collectivity in contrast to the gradual decrease near the respective ground states. The decay scheme of ²⁰²Tl has been extended from I^π = 10⁺ to I^π = 20⁺ with the identification of a new T_1/2 = 215(10)μs isomer, originating from a four-nucleon excitation. In Tl isotopes (Z = 81), with the approach of the proton shell closure at Z = 82, intrinsic excitations dominate and metastable states resulting from hindered transitions with higher multipole orders have been identified. (author)