The yield of ${\pi }^0$ mesons from gamma rays on protons has been measured as a function of center-of-mass angle for gamma-ray energies from 170 Mev to 340 Mev. The results are shown to be consistent with a model of production predominantly through a $J=\frac{3}{2}$, isotopic spin, $\frac{3}{2}$, state, which is resonant at about 300 Mev gamma-ray energy. There is evidence for $S$-state production and possibly electric quadrupole, $P$-wave production through the resonant state.

• Received 3 September 1954

DOI:https://doi.org/10.1103/PhysRev.97.188