Reciprocity Relations In Photopion Reactions

The reciprocity relation in the photopion processes $\gamma +N\rightleftarrows \pi +N^{\prime }$ as a possible test of $C_{\mathrm{st}}$ and $T_{\mathrm{st}}$ invariances of the electromagnetic interaction is discussed, where $N$ can be any nucleus or nucleon. The sensitivity of such a test is estimated for the special case $N=n or p$ in the energy range near the ($\frac{3}{2}, \frac{3}{2}$) resonance.