COOLING AND DIFFUSION IN THE GAMMA-DECAY OF ROTATING NUCLEI

A well-deformed nucleus in an excited state at high angular momentum d ecays towards the yrast line mostly by statistical dipole and rotation al quadrupole emission. We study the interplay of these two modes and show that the cooling can be viewed as a drift-diffusion process in th e two-dimensional space of energy and angular momentum. The associated master equation is solved numerically and accurate analytic approxima tions are derived. It is found that within the first quarter of the ca scade, the dependence on the initial condition is lost, and from then on the gamma-flow follows a generic behavior. The average and the vari ance of the heat energy then display a quadratic and cubic dependence on the angular momentum, respectively. Moreover, the flow obeys simple scaling laws, which can easily be applied to different regions of mas s and deformation. The results are compared to the observed intensitie s of low-lying rotational bands.