The Spin Cut-off Factor of Nuclear Level Density

Since detailed at high resolution $(n, \gamma)$ and transfer reaction data has become available, we have initiated a systematic investigation of the data in order to deduce the parameters involved in the model calculations, in particular the spin cut- off factor. It is difficult to determine experimentally the spin cut-off factor $\sigma$. We have attempted to obtain $\sigma$ near the ground state by fitting $f(J)$ to the experimental spin distribution for various nuclei with $ \chi^2=\sum_k\sum_{J_k}\{[n_k(J)-F_k(J)]^2/n_k(J)\}$ where $F_k=\sum_{J_k}n_k(J)/\sum_kf(J)$ and $n_k(J)$ being the number of levels of spin $J$ in nuclide $k$ which has the spin window $J_k^1$ and $J_k^2$. In addition the energy and mass dependence of the spin cut-off factor have been investigated using the microscopic model of BCS and reliable values for the spin cut- off factor which is often used in equilibrium decay calculations have been obtaind. The energy dependence of the effective moment of inertia determined from the deduced spin cut-off factor, $\sigma^2=(\Im_{eff}/\hbar^2)T$ for all nuclei under study will also be presented and discussed.\\\\ Work supported by the shiraz university research council through grant No. GR-Sc-52.