Further Results on the Production of Neutral Mesons by Photons

Further measurements have been made on the photoproduction of neutral mesons using the gamma-gamma coincidence technique. New data have been obtained on the gamma-gamma correlation curves in beryllium. The angular distribution of the photomesons in Be has been determined and found to be strongly peaked forward. The dependence on the atomic number $A$ of production has been found to obey an $A^{\frac{2}{3}}$ law. Some data obtained for production in hydrogen show that the ${\pi }^0$ and ${\pi }^{+}$ production cross sections are comparable and that the ${\pi }^0$ excitation curve starts more slowly from threshold than does the ${\pi }^{+}$ photo-excitation curve.