Level Density of Light Nuclei

Abstract

The level density of light nuclei ($A\le 70$) 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: $U=(E-\Delta +\frac{70}{A})$ $E$ is the usual excitation energy, $\Delta$ 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 $R\cong 1.5A^{\frac{1}{3}}$ F, $\mathcal{I}=0.7\mathrm{}{\mathcal{I}}_{\mathrm{rig}}$, $a=(0.127A)\mathrm{}$ Me${\mathrm{V}}^{-1\mathrm{}}$, 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 ($1+\Delta$) up to ∼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.