Observations on the 4.43-Mev Gamma Rays fromC12

Abstract

A scintillation spectrometer has been used for "fore and aft" measurements to demonstrate that the 4.43-Mev gamma radiation from ${\mathrm{Be}}^{9}(\ensuremath{\alpha}, n\ensuremath{\gamma}){\mathrm{C}}^{12}$ 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\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}13}$ 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\ifmmode\pm\else\textpm\fi{}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.