Proton Capture Radiation fromCa40in the Region of the Giant Resonance

The 90° differential cross section for radiative proton capture to the ground state of ${\mathrm{Ca}}^{40}$ was measured for proton energies from 6 to 15 MeV, corresponding to ${\mathrm{Ca}}^{40}$ excitation energies of 14 to 23 MeV. A giant resonance near the excitation energy of 19 MeV with a width of about 3 MeV occurs in the ${\mathrm{K}}^{39}(p, {\gamma }_0){\mathrm{Ca}}^{40}$ reaction. The giant resonance is split into eight resolved fine structure peaks between 18 and 22 MeV, and subsidiary peaks appear below the giant resonance at 15.2 and 16.2 MeV. This experiment extends the region of excitation energies studied in previous experiments, and the results are in agreement in the region of overlap. The pulse-height spectra from the gamma-ray spectrometer show a secondary gamma-ray peak with an energy corresponding to the energy of the radiation from transitions to one or more of the first four excited states of ${\mathrm{Ca}}^{40}$. The gamma rays from the individual excited-state transitions were unresolved in this experiment. The area under the secondary peak is taken as the yield of gamma rays from the ${\mathrm{K}}^{39}(p, {\gamma }_1+{\gamma }_2+{\gamma }_3+{\gamma }_4){\mathrm{Ca}}^{40*}$ reactions. The combined relative differential cross section for these reactions increases with energy by a factor of two over the range of excitation energies studied.