Proton-Capture Gamma Rays from Be8, C12, Mg24, and Ca40 in the Giant-Resonance Region

Abstract

The 90° yield for gamma rays from ${\mathrm{Be}}^8$, ${\mathrm{C}}^{12}$, ${\mathrm{Mg}}^{24}$, and ${\mathrm{Ca}}^{40}$ was determined for ($p, \gamma$) reactions using 10.4- to 14.5-MeV protons from the Columbia University variable energy cyclotron. For ${\mathrm{B}}^{11}(p, \gamma ){\mathrm{C}}^{12}$ the yields to both the first excited state and the ground state of the residual nucleus are presented. In the case of ${\mathrm{K}}^{39}(p, \gamma ){\mathrm{Ca}}^{40}$, only the ground-state yield was determined. Because the ground-state yields are very small, we report only the yield due to transitions to the first excited state for the ${\mathrm{Li}}^7(p, \gamma ){\mathrm{Be}}^8$ reaction and the combined first excited and ground-state yields for the ${\mathrm{Na}}^{23}(p, \gamma ){\mathrm{Mg}}^{24}$ reaction. In the region investigated, the yield curves exhibit a considerable amount of fine structure in all cases except ${\mathrm{Li}}^7(p, \gamma ){\mathrm{Be}}^8$. Fine-structure peaks were observed for the following excitation energies: 21.9, 22.4, 22.7, 23.0, 23.3, 24.1, 24.7, and 25.4 MeV for ${\mathrm{Na}}^{23}(p, {{\gamma }_0}^{+}{\gamma }_1){\mathrm{Mg}}^{24}$; at 18.8, 19.2, 19.5, 20.0, 21.0, and 21.7 MeV for ${\mathrm{K}}^{39}(p, {\gamma }_{\mathrm{O}}){\mathrm{Ca}}^{40}$; at 25.5, 26.9, 28.0, and 28.45 MeV for ${\mathrm{B}}^{11}(p, {\gamma }_1){\mathrm{C}}^{12}$; and at 25.5, 27.45, 28.0, and 28.9 MeV for ${\mathrm{B}}^{11}(p, {\gamma }_0){\mathrm{C}}^{12}$. A comparison with other experimental results shows that some of these peaks have not been previously observed.