Level density and $γ$-ray strength in $^{27,28}$Si

Abstract

A method to extract simultaneously level densities and $γ$-ray transmission coefficients has for the first time been tested on light nuclei utilizing the $^{28}$Si($^3$He,$αγ)^{27}$Si and $^{28}$Si($^3$He,$^3$He'$γ)^{28}$Si reactions. The extracted level densities for $^{27}$Si and $^{28}$Si are consistent with the level densities obtained by counting known levels in the respective nuclei. The extracted $γ$-ray strength in $^{28}$Si agrees well with the known $γ$-decay properties of this nucleus. Typical nuclear temperatures are found to be $T\sim 2.4$ MeV at around 7 MeV excitation energy. The entropy gap between nuclei with mass number $A$ and $A\pm 1$ is measured to be $δS\sim 1.0 k_B$, which indicates an energy spacing between single-particle orbitals comparable with typical nuclear temperatures.