Photoproduction of ChargedπMesons from Nuclei

The photoproduction of charged $\pi$ mesons by a 1000-Mev bremsstrahlung beam has been studied for the elements Be, C, Al, Cu, and Pb. Mesons with energies in the range 100 to 400 Mev emerging from the targets at angles of 58° and 115° were detected, and absolute measurements for the cross section are given. An optical model for the nucleus was employed to predict absolute upper and lower limits for the nuclear cross section, and reasonable agreement with the data was obtained. The measured cross sections had a dependence on the target atomic weight of $A^{\frac{3}{4}}$ and this result lay between the limits predicted by the model. The experimental nuclear $\frac{{\pi }^{-}}{{\pi }^{+}}$ ratio exhibited the general behavior of this quantity for deuterium, but the model could make no prediction here. The results seem to be consistent with an optical model treatment of an assumed initial production of mesons throughout the nuclear volume, and no recourse to a surface production mechanism was found to be necessary.