Mass-number and excitation-energy dependence of the spin cutoff parameter

The spin cutoff parameter determining the nuclear level density spin distribution rho(J) is defined through the spin projection as < J(z)(2)>(1/2) or equivalently for spherical nuclei, (< J(J+1)>/3)(1/2). It is needed to divide the total level density into levels as a function of J. To obtain the total level density at the neutron binding energy from the s-wave resonance count, the spin cutoff parameter is also needed. The spin cutoff parameter has been calculated as a function of excitation energy and mass with a super-conducting Hamiltonian. Calculations have been compared with two commonly used semiempirical formulas. A need for further measurements is also observed. Some complications for deformed nuclei are discussed. The quality of spin cut off parameter data derived from isomeric ratio measurement is examined.