Cross sections for (π+,p) reactions onLi6,Be9,C12, andO16

Abstract

Measurements of the (${\pi }^{+},p$) reaction on ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$, ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ have been made for 70-MeV pions. A magnetic spectrometer was used to momentum analyze the pion beam while thick Nal(T1) detectors were used to determine the proton energy. The experimental resolution was 3 MeV. Data from the ${}_{}{}^9{}_{}{}^{}\mathrm{Be}$ and ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ targets were taken around a laboratory scattering angle of 25°. The number of (${\pi }^{+},p$) events from these nuclei was not significantly greater than background contributions, and therefore upper limits on the corss section are presented. Data from the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({\pi }^{+},p){}_{}{}^{11}{}_{}{}^{}\mathrm{C}$ reaction were obtained at proton emission angles of 20 and 32° (lab), while for ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$, measurements were made over the angular range from 33 to 90°. Our experimental cross section for the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({\pi }^{+},p){}_{}{}^{11}{}_{}{}^{}\mathrm{C}$ reaction, obtained by integrating over ${}_{}{}^{11}{}_{}{}^{}\mathrm{C}$ excitation energies from 0 to 8 MeV, did not agree well with existing theoretical predictions. Results from the ${}_{}{}^6{}_{}{}^{}\mathrm{Li}({\pi }^{+},p){}_{}{}^5{}_{}{}^{}\mathrm{Li}$ reaction indicated excitation of the $p_{\frac{1}{2}}$ state of ${}_{}{}^5{}_{}{}^{}\mathrm{Li}$. The cross section for this reaction decreased rapidly for emission angles less than 60°, while at larger angles the cross section was constant within the measured range.