The direct detection of neutrons from ($\gamma , n$) reactions induced by betatron bremsstrahlung has been applied to cross-section determinations using gaseous targets at approximately 100 atmospheres pressure. Results from oxygen are consistent with other determinations. The remaining elements represent new results and show the familiar giant dipole resonance for the photoneutron process. Parameters of the resonances are determined and related to the systematic behavior previously reported for other elements.

• Received 1 April 1954

DOI:https://doi.org/10.1103/PhysRev.95.776