(γ, p) Reaction in Argon-40

The energy distribution and angular distribution of photoprotons from argon irradiated with 22.5-Mev bremsstrahlung have been measured. The yield of protons was found to be 6.6×${10}^5$ protons per mole per r, in good agreement with Saskatoon results. The angular distribution of protons indicated that the absorption was predominantly electric dipole, as expected. The energy distribution peaked at 2.6 Mev, and, from its characteristics, it was inferred that the Coulomb barrier for protons plus ${\mathrm{Cl}}^{39}$ was only about 2.5 Mev, and that the level density in ${\mathrm{Cl}}^{39}$ increased with energy approximately as $\exp \mathrm{}\left(E\right)\mathrm{}$. These result are discussed in terms of the compound nucleus model and the direct photoeffect model.