Investigation of the level density parameters for all mass range with semi-classical methods

In this thesis level density parameters have been investigated for nuclei from all mass range and also some light exotic nuclei. By using a systematic that all level density parameters treated as free parameters and adjusted to experimental values, the changing with excitation energy or nucleon number of these parameters has been obtained. With this investigation, it has been seen that the level density parameter a should be a Laplace distribution of excitation energy around 2 MeV, which the energy region that collective effects dominate, instead of exponential decay. The semi-classical level density model which underlies this work is already the most compatible model to mean resonance spacing, also it has been understood that to achieve the same success for discrete levels these effects should be included to model. With this purpose, a new formula for the level density parameter a has been offered to include the collective effects. The calculations made by this formula increased the agreement with the experimental values and also showed that there is no need to some free parameters for phenomenological level density models. This situation also abrogated the fitting procedure for parameter values to observables of stable nuclei, and it has become possible to make calculations for nuclei far from stability. As a conclusion, the level density model which is introduced in this work is appropriate to use in low energy reactions of light exotic nuclei, which is very important for astrophysical applications of nuclear physics.