Beta Decays and Delayed Gammas from Fission Fragments

A theoretical study is made of the gross behavior of beta decays following nuclear fission in times from ${10}^{-2\mathrm{}}$ to 10 sec. First a simple model is formulated to describe the situation in terms of a few parameters. Then the most uncertain of these parameters are chosen to fit the observed rate of delayed gamma emission (assumed proportional to the beta-decay rate) for the ${\mathrm{U}}^{235}(n, f)$ process. The description is extended to other isotopes by assuming that they differ only by small shifts of their initial fragment distributions away from that appropriate to neutron-induced fission of ${\mathrm{U}}^{235}$. The result is a theoretical summary of the presently available data which can be used in predictive extrapolation of that data to situations not yet studied experimentally.