28- and 34-MeVLi6andLi7elastic scattering on nuclei with40≤A≤91

Abstract

$^{6}\mathrm{Li}$ and $^{7}\mathrm{Li}$ elastic scattering were measured at 28 and 34 MeV on $^{40}\mathrm{Ca}$ and $^{48}\mathrm{Ca}$ to $\frac{\ensuremath{\sigma}}{{\ensuremath{\sigma}}_{R}}l{10}^{\ensuremath{-}3}$. An anomalous back angle enhancement was seen for $^{6}\mathrm{Li}$ + $^{40}\mathrm{Ca}$. No set of optical model parameters tried was able to fit the back angle $^{6}\mathrm{Li}$ + $^{40}\mathrm{Ca}$ data. Optical model parameters which exhibited a continuous Igo ambiguity but no discrete ambiguities were obtained for the above reactions and for other Li elastic scattering on $^{62}\mathrm{Ni}$, $^{63}\mathrm{Cu}$, $^{64}\mathrm{Zn}$, $^{68}\mathrm{Zn}$, $^{90}\mathrm{Zr}$, and $^{91}\mathrm{Zr}$. For a given value of the diffuseness, all parameter sets related by the Igo ambiguity gave completely identical fits to data. The value of the diffuseness which yielded acceptable fits was limited to a narrow range. It was found that the optical model parameters are extremely sensitive to the absolute normalization of the data. An empirical formula for the optical model parameters as a function of $N$ and $Z$ of the target nucleus was obtained for both $^{6}\mathrm{Li}$ and $^{7}\mathrm{Li}$ elastic scattering on these targets.NUCLEAR REACTIONS $^{40}\mathrm{Ca}$($^{6}\mathrm{Li}$, $^{6}\mathrm{Li}$), $^{40}\mathrm{Ca}$($^{7}\mathrm{Li}$, $^{7}\mathrm{Li}$), $^{48}\mathrm{Ca}$($^{6}\mathrm{Li}$, $^{6}\mathrm{Li}$), $^{48}\mathrm{Ca}$($^{7}\mathrm{Li}$, $^{7}\mathrm{Li}$); $E=28 \mathrm{and} 34$ MeV; measured $\ensuremath{\sigma}(\ensuremath{\theta})$, ${\ensuremath{\theta}}_{\mathrm{lab}}=10\ensuremath{-}165\ifmmode^\circ\else\textdegree\fi{}$; deduced optical model parameters. Deduced systematic optical model parameters Li+$^{40}\mathrm{Ca}$, $^{48}\mathrm{Ca}$, $^{63}\mathrm{Cu}$, $^{64}\mathrm{Zn}$, $^{68}\mathrm{Zn}$, $^{90}\mathrm{Zr}$, $^{91}\mathrm{Zr}$.