Impact of the quenching of shell effects with excitation energy on Nuclear Level Density

Abstract

We investigate the nature and impact of shell effects on nuclear level density (NLD) and particle emission probability as a function of temperature in a microscopic theoretical framework of Statistical Model for nuclei ranging from neutron deficient to neutron rich isotopes of Z$=$ 27$-$35. Critical temperatures are traced for neighbouring even, odd, closed shell and mid$-$shell nuclei which respond to excitations differently due to their varying stability and structural effects. Importance of the shell effects and shell correction energy is reflected significantly in NLD variation which slowly diminishes with increasing excitation energy indicating the quenching of shell effects. The enhancement of LD parameter with the deformation and rotation and the fade out of enhancement with increasing excitations has been shown. The weakening of magicity of N$=$28 near the proton drip line has been observed in the inverse level density parameter 'K'($=$ A/a) and $\beta$ variation though it is usually uncommon to see this effect in excited nuclei. Variation of our calculated NLD for odd $^{69}$As and even $^{70}$Ge exhibits structural effects and agrees very well with the variation of experimental values. Our evaluated level density parameter 'a' values are compared with RIPL-2 (Reference Input Parameter Library) data which show good agreement.