مهدی سلطانی

In theory, knowledge of the nuclear level density is important. According to the Fermi golden rule, level density has a important role in estimating the nuclear reactions. To obtain the level density, is needed spin cut off factor. This factor shows the width’s distribution of angular momentum of level density. Values obtained for level density parameters is dependent to used expression for spin cut off factor. So, it is necessary to have an appropriate description from this factor. Different expressions provided for spin cut off factor. In this thesis, with using the most recent data available for about 70 nucleus, counting the different modes of spin and using the least square fitting, spin cut off factor was calculated for above nucleus and dependents of it checked in examine the mass number. It is noticeable that already done calculations for light nucleus, with different relations (Gilbert –Cameron and Zhong fu Huang relations and von Egidy) that uses for spin cut off factor, is consistent.