A scintillation spectrometer has been used for "fore and aft" measurements to demonstrate that the 4.43-Mev gamma radiation from ${\mathrm{Be}}^9(\alpha , n\gamma ){\mathrm{C}}^{12}$ exhibits a Doppler shift as the result of motion of the emitting nucleus. This implies a lifetime for the ${\mathrm{C}}^{12}$ excited state less than 3×${10}^{-13\mathrm{}}$ second. The Compton electron spectrum from a thin converter has been studied in a magnetic lens spectrometer to produce a value for the level excitation of 4.425±0.020 Mev. The spectrum of internal pairs has been found to agree most closely (to 5 percent) with the (known) assignment of the radiation as electric quadrupole.

• Received 24 May 1954

DOI:https://doi.org/10.1103/PhysRev.95.1206