A bremsstrahlung-photon difference method measurement of the ${\mathrm{Be}}^9(\gamma , n)$ cross section indicates maxima in the cross section of 1.15±0.15, 0.55±0.1, 1.2±0.2, and 1.0±0.3 mb at energies of 1.70, 2.40, 2.95, and 4.6 Mev, respectively. The angular distribution of the neutrons corresponding to the 1.70- and 4.6-Mev peaks is spherically symmetric; $\frac{d\sigma }{d\Omega }=a+b{sin}^2\theta (\frac{a}{b}=1.0\mathrm{}\pm 0.2)$ for the 2.95-Mev peak.

• Received 21 February 1961

DOI:https://doi.org/10.1103/PhysRev.123.229