A recently reported measurement of the photoneutron cross section for ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ indicates a value of about 1.0 mb for $E_x$ of ∼23 to ∼33 MeV. This result, when combined with the previously reported ($\gamma ,p$) cross section in this energy region, implies a ($\gamma ,p$)-to-($\gamma ,n$) cross section ratio of 1.6 to 1.9 in the 26 to 29 MeV region of ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. We have used the inverse reaction ${}_{}{}^3{}_{}{}^{}\mathrm{He}(n,\gamma ){}_{}{}^4{}_{}{}^{}\mathrm{He}$ to measure the photoneutron cross section for ${}_{}{}^4{}_{}{}^{}\mathrm{He}$. Our detailed balanced results confirm the recently reported measurements.

[NUCLEAR REACTIONS ${}_{}{}^3{}_{}{}^{}\mathrm{He}(n,\gamma ){}_{}{}^4{}_{}{}^{}\mathrm{He}$; measured $\sigma (E;\theta )$, $E=6.0\mathrm{} \mathrm{to} 17.0$ MeV. Results confirm the most recent ${}_{}{}^4{}_{}{}^{}\mathrm{He}(\gamma ,n){}_{}{}^3{}_{}{}^{}\mathrm{He}$ measurements.]

• Received 17 February 1981

DOI:https://doi.org/10.1103/PhysRevC.24.317