Level density parameter in exotic nuclei of mass [formula omitted] from proton and alpha evaporation spectra

Abstract

Proton and alpha spectra in the energy range E p c.m. ∼6 –24 MeV and E α c.m. ∼12 –40 MeV, respectively, have been measured in the reaction 28 Si+ 58 Ni at E lab ( 28 Si)=100 and 125 MeV. The spectra at various laboratory angles from 100° to 160° were corrected for angular distribution effects to obtain the angle-integrated spectra. An asymptotic (liquid drop) level density parameter of a ̃ =A/7.5 describes the proton and alpha spectra at both the beam energies. No lowering of emission barrier is needed to explain the alpha spectra although the spin dependence of level density has to be tuned. The derived value of a ̃ is somewhat larger than that for other near-stable nuclei and possibly arises due to the excitation energy dependent collective enhancement of the nuclear level density.