Photoprotons from Lead-208 and Tantalum

The photoprotons ejected from thin foils of tantalum and enriched lead-208 by the 23-Mev bremsstrahlung x-rays from a betatron have been observed in nuclear emulsions. Yields, measured in units of 10⁴ protons per mole per roentgen unit, are: tantalum, 5.6±{}0.5; lead-208, 2.6±{}0.3. The angular distribution of the lead-208 protons shows a strong forward asymmetry while the tantalum protons are more isotropic. Both proton energy distributions are in good agreement with the predictions of the direct photoprocess.