The total photoelectric cross sections of copper, molybdenum, silver, tantalum, and gold have been measured at 662 kev. A highly collimated beam of gammas from a Cs-137 source impinged upon a thin disk of a target material. Photoelectrons from a target were detected by a plastic scintillator subtending very nearly $4\pi$ steradians. Pulse-height analysis permitted partial resolution of photoelectric and Compton events. After subtraction of unresolved Compton events and correction for coherent scattering effects, the cross sections were found to be 0.125±0.009, 0.700±0.016, 1.198±0.028, 8.55±0.14, and 11.62±0.16 barns, respectively, in satisfactory agreement with theory.

• Received 24 February 1959

DOI:https://doi.org/10.1103/PhysRev.115.351