Gamma-ray spectra taken in prompt coincidence with incident 180-MeV ${\pi }^{+}$, 220-MeV ${\pi }^{-}$, and 0-MeV ${\pi }^{-}$ on the self-conjugate targets ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}$ show that the cross sections/yields are equal to or near zero for production of the $J^{\pi }$,$T=0^{+},1\mathrm{}$ levels of the odd $Z$, odd $N$ nuclei resulting from $\mathrm{np}$ removal. The 0-MeV ${\pi }^{-}$ results can be explained by selection rules governing one-step quasifree interactions, but the $\Delta \mathrm{}\left(1232\right)\mathrm{}$ region results cannot. This suggests that there may be additional restrictions upon the pion absorption mechanism.

NUCLEAR REACTIONS ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}({\pi }^{\pm },X\gamma ){}_{}{}^{10}{}_{}{}^{}\mathrm{B}$, ${}_{}{}^{32}{}_{}{}^{}\mathrm{S}({\pi }^{\pm },X\gamma ){}_{}{}^{30}{}_{}{}^{}\mathrm{P}$; $E_{{\pi }^{-}}=0\mathrm{} \mathrm{MeV}, 220 \mathrm{MeV}$; $E_{{\pi }^{+}}=180\mathrm{}$ MeV; detected $\gamma$ rays, Ge(Li); measured $E_{\gamma }$, 90° $\sigma$ and $Y$ (%) for $\mathrm{np}$ removal; deduced reaction mechanism.

• Received 27 May 1980

DOI:https://doi.org/10.1103/PhysRevC.23.2150