Using a Halpern-type photoneutron detection system, the photoneutron yields from Li, ${\mathrm{N}}^{14}$, and ${\mathrm{A}}^{40}$ have been measured as a function of the maximum bremsstrahlung energy from threshold to approximately 50 Mev. The method of Penfold and Leiss was used to extract from the yield curves the total neutron cross section; ${\sigma }_T=\sigma (\gamma , n)+\sigma (\gamma , pn)+2\mathrm{}\sigma (\gamma , 2n)+\cdots$. The results are compared with previous findings of other laboratories. No gross structure was detected in the lithium cross section in the giant resonance region. The data indicate that lithium has a high-energy tail on the cross section of considerable magnitude.

• Received 13 November 1959

DOI:https://doi.org/10.1103/PhysRev.118.535