Systematics of Photoproton Reactions

The photoproton yields from the elements Ta, Pt, Pb, W, and Au have been determined for betatron bremsstrahlung bombardment at 22-Mev peak energy by the use of zinc sulfide detectors and a 40-{μ}sec betatron pulse duration. The yields, as measured in photoprotons per mole per roentgen, are as follows: Ta, 5.7×{}10⁴; Pt, 2.9×{}10⁴; Pb, 5.8×{}10⁴; W, 5.2×{}10⁴ and Au, 1.9×{}10⁴. These values, along with previous determinations, permit a study of general behavior of photoproton yields for all Z values throughout the periodic table. Comparisons with calculations based on the evaporation model show good agreement with experimental trends up to a Z of 50, after which the measured yields are too high by factors ranging from 10 to 10⁴. Calculations based on the direct photoelectric process give better agreement.