The angular distributions of the neutrons from the reactions ${\mathrm{Be}}^9(n, n^{\prime }){\mathrm{Be}}^{9*}$, $Q=-2.43\mathrm{}$ Mev, and ${\mathrm{C}}^{12}(n, n^{\prime }){\mathrm{C}}^{12*}$, $Q=-4.43\mathrm{}$ Mev, have been measured from 25° to 140°, employing 14-Mev incident neutrons. Neither distribution is symmetric about 90°; the inelastically scattered neutrons are peaked in the forward direction. The ${\mathrm{C}}^{12}(n, n^{\prime })$ first-level angular distribution, which agrees with a recent measurement of the ${\mathrm{C}}^{12}(p, p^{\prime })$ distribution, is in good agreement with the prediction of the Levinson-Banerjee direct interaction theory. The integrated inelastic scattering cross sections for the ${\mathrm{Be}}^9$ and ${\mathrm{C}}^{12}$ first levels are 0.17±0.03 barn and 0.22±0.03 barn, respectively.

The 4.43-Mev de-excitation gamma rays from ${\mathrm{C}}^{12*}$ are symmetric about 90°. The gamma-ray production cross section at 90° is 13.1±2.0 mb/sterad. No gamma rays associated with ${\mathrm{Be}}^{9*}$ are seen. It is concluded that about one-third of the ($n, 2n$) cross section at 14 Mev is a two-stage process proceeding via the 2.43-Mev level in ${\mathrm{Be}}^9$.

• Received 11 March 1958

DOI:https://doi.org/10.1103/PhysRev.111.572