Investigation of the level density parameter using evaporativeα-particle spectra from the19F+181Tareaction

Abstract

Light charged particles in coincidence with evaporation residues from the ${}^{19}\mathrm{F}{+}^{181}{\stackrel{\ensuremath{\rightarrow}}{\mathrm{Ta}}}^{200}\mathrm{Pb}$ reaction have been studied at ${E}_{\mathrm{lab}}=121,$ 154, 179, and 195 MeV with the aim of determining, within the context of the statistical model, a possible dependence of the Fermi-gas level density parameter on the temperature/excitation energy of the emitting system. Angular distributions of evaporation residues and of fission fragments, along with fission fragment folding angle distributions, were also measured. A moderate excitation energy dependence of the level density parameter, as given by recent theoretical calculations, is consistent with the measured $\ensuremath{\alpha}$-particle spectral shapes. Although the spectra are reproduced best with a weakly varying level density parameter, a constant level density parameter of a=A/12 ${\mathrm{MeV}}^{\ensuremath{-}1}$ cannot be excluded.