Cross sections for production of the 15.10-MeV and other astrophysically significant gamma-ray lines through excitation and spallation of 12C and 16O with protons.

Abstract

The ratio of the flux of 15.10-MeV gamma rays to the flux of 4.438-MeV gamma rays resulting from excitation of the corresponding states in $^{12}\mathrm{C}$ is a sensitive measure of the spectrum of the exciting particles produced in solar flares and other cosmic sources. These gamma rays are produced predominantly by interactions with $^{12}\mathrm{C}$ and $^{16}\mathrm{O}$, both of which are relatively abundant in the solar photosphere. Gamma-ray production cross sections for proton interactions have been reported previously for all important channels except for the production of 15.10-MeV gamma rays from $^{16}\mathrm{O}$. The first reported measurement of the 15.10-MeV gamma-ray production cross section from p${+\mathrm{}}^{16}$O is presented here. A cyclotron was employed to produce 40-, 65-, and 85-MeV protons which interacted with ${\mathrm{CH}}_{2}$ and BeO targets. The resultant gamma-ray spectra were measured with a high-purity germanium semiconductor detector at 70, 90, 110, 125, and 140 deg relative to the direction of the incident beam for each proton energy. Other gamma-ray lines resulting from direct excitation and spallation reactions with $^{12}\mathrm{C}$ and $^{16}\mathrm{O}$ were observed as well, and their gamma-ray production cross sections, several of which have not been reported previously, are presented. The results are compared with previously reported measurements, as available.