The 3367-keV ground-state $\gamma$-ray transition from the reaction ${}_{}{}^9{}_{}{}^{}\mathrm{Be}(n_{\mathrm{th}}, \gamma ){}_{}{}^{10}{}_{}{}^{}\mathrm{Be}$ shows no Doppler broadening from recoil imparted by emission of $\gamma$ rays populating this level. This result is consistent with the known lifetime of this level, which is larger than the estimated slowing-down time of the recoil nucleus in the sample medium.

• Received 21 April 1969

DOI:https://doi.org/10.1103/PhysRev.186.1292