Emission of High-Energy Gamma Line fromC12

A gamma ray of energy 15.2 Mev has been observed with a 180° pair spectrometer in the bombardment of carbon by protons of energy 30-340 Mev. The line is also seen in deuteron bombardment of ${\mathrm{B}}^{11}$, but not of ${\mathrm{B}}^{10}$. These facts, along with energetics arguments and clear spectrometer separation from known lines in excited ${\mathrm{Be}}^8$, strongly indicate an excited ${\mathrm{C}}^{12}$ origin for the line. It is tentatively proposed that the excited ${\mathrm{C}}^{12}$ level here involved is a $T=1\mathrm{}$ state for which isotopic spin selection rules forbid a disintegration into three alpha particles.