Energy spectra and angular distribution of photoneutrons from carbon are studied by irradiation with a 30-Mev bremsstrahlung beam. The spectra exhibit a fine structure from which the following levels in ${\mathrm{C}}^{12}$ may be distinguished: 21.4, 22.2, 22.9, 23.6, (24.3), 24.8, and 25.6 Mev. Many of these coincide with levels found in the ${\mathrm{C}}^{12}(\gamma , p)$ and ${\mathrm{C}}^{12}(\gamma , 3\alpha )$ reactions.

Photoneutron emission occurs predominantly by transition to the ground state of ${\mathrm{C}}^{11}$.

The angular distribution is of the form $1+1.5{sin}^2\theta$ for all neutrons having energy $E_n>3\mathrm{}$ Mev. This distribution agrees with that expected according to Wilkinson's independent-particle model for ejection from the $l=1\mathrm{}$ orbit.

• Received 5 January 1960

DOI:https://doi.org/10.1103/PhysRev.118.1297