Surface transparency inC12elastic scattering fromCa40,42,48

Abstract

Angular distributions between 3 and 110 degrees in the laboratory system were measured for the elastic scattering of $^{12}\mathrm{C}$ from $^{40,42,48}\mathrm{Ca}$ at 51.0, 49.9, and 47.2 MeV, respectively. Pronounced oscillations were observed in the $^{12}\mathrm{C}$ + $^{40}\mathrm{Ca}$ angular distribution. Weaker oscillations were observed in the $^{12}\mathrm{C}$ + $^{42}\mathrm{Ca}$ angular distributions while none were seen in $^{12}\mathrm{C}$ + $^{48}\mathrm{Ca}$. An optical-model analysis was performed using Woods-Saxon and folded potentials. Surface transparent potentials were found to parametrize the oscillatory structure of the forward-angle data of $^{12}\mathrm{C}$ + $^{40}\mathrm{Ca}$. Stronger surface absorption in the $^{12}\mathrm{C}$ + $^{42,48}\mathrm{Ca}$ imaginary potentials apparently weakens or washes out any forward-angle oscillations. Optical potentials that fit forward-angle data of $^{12}\mathrm{C}$ + $^{40}\mathrm{Ca}$ also predict oscillatory structure in the excitation function at 180\ifmmode^\circ\else\textdegree\fi{}.NUCLEAR REACTIONS $^{40}\mathrm{Ca}$($^{12}\mathrm{C}$, $^{12}\mathrm{C}$)$^{40}\mathrm{Ca}$, $E=51$ MeV; measured $\ensuremath{\sigma}(\ensuremath{\theta})$, measured $\ensuremath{\sigma}(E,\ensuremath{\theta}=180\ifmmode^\circ\else\textdegree\fi{})$. $^{42}\mathrm{Ca}$($^{12}\mathrm{C}$, $^{12}\mathrm{C}$)$^{42}\mathrm{Ca}$, $E=49.9$ MeV; $^{48}\mathrm{Ca}$($^{12}\mathrm{C}$, $^{12}\mathrm{C}$)$^{48}\mathrm{Ca}$, $E=47.2$ MeV; measured $\ensuremath{\sigma}(\ensuremath{\theta})$.