Photoproduction of ChargedπMesons from Nuclei

The $\gamma$-ray beam from the Cornell synchrotron was used to investigate the photoproduction of low-energy charged $\pi$ mesons from several nuclei at 35° to the beam direction. Maximum photon energies used were 800 Mev and 1 Bev. The yields of 40 and 80 Mev ${\pi }^{+}$ and 40 Mev $\pi$ mesons were observed with a detection system whose aperture was known absolutely. It was found that in some cases the meson yields were proportional to the atomic number, $A$, of the target rather than the more usual $A^{\frac{2}{3}}$. The data are compared with the predictions of an optical model of the nucleus. The deviations observed can be partially explained in terms of the inelastic scattering of high-energy mesons and of multiple meson production. An excitation function was measured for 80 Mev ${\pi }^{+}$ mesons from carbon by varying the machine energy; this indicated the presence of an appreciable number of multiply produced mesons.