Isoscalar Giant Resonance in Light Nuclei (A<~40)

Abstract

The giant-resonance region was studied for ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$, ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ar}$, ${}_{}{}^{36}{}_{}{}^{}\mathrm{Ar}$, ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$, ${}_{}{}^{28}{}_{}{}^{}\mathrm{Si}$, ${}_{}{}^{27}{}_{}{}^{}\mathrm{Al}$, ${}_{}{}^{20}{}_{}{}^{}\mathrm{Ne}$, and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ by inelastic scattering of 96.6-MeV $\alpha$ particles. A systematic broadening of the isoscalar giant resonance at $E_{\mathrm{exc}}\simeq \frac{63}{A^{\frac{1}{3}}}$ MeV occurs as $A$ decreases. The width for ${}_{}{}^{40}{}_{}{}^{}\mathrm{Ca}$ is 3.5±0.3 MeV, for ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ it is 7.1±0.5 MeV, and for nuclei below $A=32\mathrm{}$ the resonance is too diffuse to be observed.