Search for fadeout of collectivity in nuclear level density

Nuclear level density (NLD) is an essential ingredient in nuclear reaction code to calculate reaction cross-sections. Nuclear level density is generally described semi empirically using Fermi Gas model. Fermi Gas model does not however account for the microscopic effects such as shell structure, pairing correlation and collective excitation in the nuclear level density. These are generally incorporated phenomenologically in this model. Collective excitation has a significant effect on nuclear level density particularly for deformed nuclei. For nuclei with appreciable ground-state deformations, it has been conjectured by Ignatyuk et al. that, at low excitation energies, there should be collective enhancement of NLD due to the coupling of the rotational as well as the vibrational degrees of freedom with the single particle degrees of freedom. The enhanced level density ρ(E∗, J) may be expressed as ρ(E∗, J) = ρ_int(E∗, J)K_coll(E∗), ρ_int being the single particle level density and K_coll the collective enhancement factor