Towards a shell-model description of the low-energy structure of deformed nuclei II. Electromagnetic properties of collective M1 bands

Abstract

A shell-model theory, called the pseudo SU(3) model, which was proposed previously for giving the structure of low-lying states in heavy deformed nuclei is used to predict the number of 1 + states with strong M1 transitions to ground states for the nuclei 154Sm, 156 160Gd, 164Dy, 168Er, 174Yb of the rare earth region and the actinide species 232Th, 234 240U, 242Pu. Results are also given for E2 and M3 transition strengths in these nuclei. The measures provide a rigorous test of the theory, which in reality is a many-particle Nilsson scheme, because the real M1, E2, and M3 operators are used in the calculations. It is found that the results for E2 strengths using the real quadrupole operator Q differ by less than 5% from those of calculations that use the operator Q ̃ which is a generator of the pseudo SU(3) symmetry. This is so even for weak interband transitions. To further test the theory additional experimental information on the 2 γ + states is necessary. In particular, the 1 + → 2 γ + decay strengths are needed to differentiate between theories for the structure of the giant M1 states.