Excitation functions for reactions induced by ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ particles in Be, C, O, and F were determined by irradiating thin foils of beryllium, Mylar, Teflon, and nylon with ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ ions of energies from 3 to 10 MeV. The radioactive products were assayed by gamma spectrometry, and their decay curves fitted by least-squares analysis. The maximum cross sections (and corresponding ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ energies) were ${}_{}{}^9{}_{}{}^{}\mathrm{Be}({}_{}{}^3{}_{}{}^{}\mathrm{He},n){}_{}{}^{11}{}_{}{}^{}\mathrm{C}$, 113±11 mb (4.3 MeV); ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({}_{}{}^3{}_{}{}^{}\mathrm{He},n){}_{}{}^{14}{}_{}{}^{}\mathrm{O}$, 16.5±1.8 mb (6.3 MeV); ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({}_{}{}^3{}_{}{}^{}\mathrm{He},d){}_{}{}^{13}{}_{}{}^{}\mathrm{N}$, 98.9±12.2 mb (9.5 MeV); ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({}_{}{}^3{}_{}{}^{}\mathrm{He},\alpha ){}_{}{}^{11}{}_{}{}^{}\mathrm{C}$, 366±26 mb (8.2 MeV); ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}({}_{}{}^3{}_{}{}^{}\mathrm{He},p){}_{}{}^{18}{}_{}{}^{}\mathrm{F}$ 436±44 mb (6.3 MeV); ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}({}_{}{}^3{}_{}{}^{}\mathrm{He},\alpha ){}_{}{}^{15}{}_{}{}^{}\mathrm{O}$, 169±17 mb (6.6 MeV); ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}({}_{}{}^3{}_{}{}^{}\mathrm{He},\alpha ){}_{}{}^{18}{}_{}{}^{}\mathrm{F}$, 22.1±2.0 mb (7.1 MeV); and ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}({}_{}{}^3{}_{}{}^{}\mathrm{He},\alpha n){}_{}{}^{17}{}_{}{}^{}\mathrm{F}$, 50.4±5.0 mb (8.2 MeV). Results for some of these reactions, previously obtained by other workers, were in reasonable agreement with our data; in particular, the fine structure of the reaction ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({}_{}{}^3{}_{}{}^{}\mathrm{He},n){}_{}{}^{14}{}_{}{}^{}\mathrm{O}$ was confirmed in these experiments. An integral excitation function, calculated from the differential data of Towle and Macefield for the ${}_{}{}^9{}_{}{}^{}\mathrm{Be}({}_{}{}^3{}_{}{}^{}\mathrm{He},n){}_{}{}^{11}{}_{}{}^{}\mathrm{C}$ reaction, agreed with the integral data obtained in this work. The distorted-wave theory of direct reactions was used to compute excitation functions for comparison with integral data for ${}_{}{}^3{}_{}{}^{}\mathrm{He},\alpha$ reactions on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$, and ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$, and for the (${}_{}{}^3{}_{}{}^{}\mathrm{He},d$) reaction on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$. The results of the comparison between theory and experiment indicate that a direct mechanism is operative in all the cases studied, except the ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({}_{}{}^3{}_{}{}^{}\mathrm{He},\alpha ){}_{}{}^{11}{}_{}{}^{}\mathrm{C}$ reaction, which appears to proceed to a large extent by way of a compound-nucleus reaction. Thus, the integral data indicate that the primary mechanisms operative in the reactions (${}_{}{}^3{}_{}{}^{}\mathrm{He},\alpha$) on ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$ and ${}_{}{}^{19}{}_{}{}^{}\mathrm{F}$, and (${}_{}{}^3{}_{}{}^{}\mathrm{He},d$) on ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$, are respectively direct pickup and stripping.

• Received 27 January 1966

DOI:https://doi.org/10.1103/PhysRev.146.650