Level Density of Light Nuclei

Abstract

The level density of light nuclei ($A\ensuremath{\le}70$) is studied by analyzing statistical reaction spectra, slow-neutron resonances, and level widths at high excitation energy. Further evidence seems to indicate that, as proposed in a preceding work, the effective excitation energy of excited nuclei, appearing in the Lang-Le Couteur level-density formula, must be calculated by means of the following expression: $U=(E\ensuremath{-}\ensuremath{\Delta}+\frac{70}{A})$ $E$ is the usual excitation energy, $\ensuremath{\Delta}$ is the pairing energy, and $\frac{70}{A}$ MeV is a term that shifts, in a smooth manner, the zero of the energy scale of different nuclei. In this case the Lang-Le Couteur formula, assuming $R\ensuremath{\cong}1.5{A}^{\frac{1}{3}}$ F, $\mathcal{I}=0.7{\mathcal{I}}_{\mathrm{rig}}$, $a=(0.127A)$ Me${\mathrm{V}}^{\ensuremath{-}1}$, gives, without further changes of its parameters, a correct estimation of the slope and absolute value of the level densities of light nuclei for energies ranging from ($1+\ensuremath{\Delta}$) up to \ensuremath{\sim}20 MeV. It is also shown that the preceding choice of the parameters of Lang-Le Couteur level-density expression allows one to reproduce very well the experimental distributions of low-energy levels observed with reactions which proceed, at least partially, through the formation of a compound nucleus.