Production ofπ∘Mesons in Hydrogen and Deuterium by High Energyγ-Rays

The angular distribution of the ${\pi }^{\circ }$'s and the dependence of the cross sections on the energy of the $\gamma$-rays have been studied for the reactions $\{\gamma +P,\to {\pi }^{\circ }+P,\}\{\gamma +P,\to {\pi }^{\circ }+D(P,N).\}$ For the first reaction, the angular distribution in the center-of-mass system has the form $a+b{sin}^2\overline{\theta }$, with $\frac{a}{b}\simeq 1$, and the cross section is proportional to approximately the square of the excess energy of the $\gamma$-rays above the threshold; $\frac{{\sigma }_{\mathrm{D}}}{{\sigma }_{\mathrm{H}}}\simeq 2$ at all energies and angles.