Charged Photomesons from Various Nuclei

The yield of ${\pi }^{-}$ and ${\pi }^{+}$ photomesons from a wide range of nuclei has been measured. The irradiating photon flux was 310-Mev bremsstrahlung and the mesons were selected magnetically at 135° with an energy of 65±15 Mev. The experimental results include the following features: (1) the $\frac{{\pi }^{-}}{{\pi }^{+}}$ ratio from deuterium is close to unity; (2) the charged meson cross sections for deuterium are close to that for hydrogen; (3) the total charged meson cross section per nucleus varies as $A^{\frac{2}{3}}$; (4) the $\frac{{\pi }^{-}}{{\pi }^{+}}$ ratios show a remarkable correlation with the masses of the isobars adjacent in $Z$ to the target nucleus; (5) the $\frac{{\pi }^{-}}{{\pi }^{+}}$ ratio from beryllium is energy sensitive. The implications of these results are discussed.