Nuclear level-density parameters of nuclei in theZ~70andA~180mid-shell regions

Abstract

$\ensuremath{\alpha}$-particle evaporation energy spectra have been measured as a function of $\ensuremath{\gamma}$-ray fold for various target-projectile systems leading to residual nuclei in the range of $Z~70$ and $A~180$ with excitation energy of 30--40 MeV. The inverse level-density parameter $K$ was determined for various nuclei by comparing the high-energy part of the $\ensuremath{\alpha}$-particle evaporation spectra with PACE2 predictions. It is observed that the inverse level-density parameter remains constant for all systems studied in this work within statistical errors in the angular momentum range of 15--30 $\ensuremath{\hbar}$. The fold-gated $\ensuremath{\alpha}$-particle energy spectra in these systems are well reproduced by the PACE2 code with a level-density parameter value of $A/(8.2\ifmmode\pm\else\textpm\fi{}1.1)$ MeV${}^{\ensuremath{-}1}$.