Simple Capture of Alpha-Particles

Gamma-rays have been observed from the simple capture of alpha-particles in lithium. The gamma-ray energies were too large for simple capture in ${\mathrm{Li}}^6$, but not inconsistent with the reaction ${\mathrm{Li}}^7(\alpha ,\gamma ){\mathrm{B}}^{11}$. Three resonances were observed at bombarding energies of 0.401, 0.819, and 0.958 Mev. The corresponding excited states in ${\mathrm{B}}^{11}$ are at 8.90, 9.16, and 9.25 Mev. The yields were too small to use thin targets, but the resonances appeared as steps in the thick target yield curve. The slope of the steps was largely of instrumental origin for the first two resonances and suggested a width of about six kev for the upper resonance. Among the other light elements, only Be and B yielded gamma-rays when bombarded by 1.4-Mev alpha-particles; but in these cases, the sharp resonances characteristic of simple capture were absent.