Strong spin-isospin mode isovector analog states were studied in differential cross section measurements ($0.6\lesssim q\lesssim 1.5$ ${\mathrm{fm}}^{-1\mathrm{}}$) of the reaction ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}(\gamma , {\pi }^{+}){}_{}{}^{13}{}_{}{}^{}\mathrm{B}$ up to 12 MeV excitation energy in ${}_{}{}^{13}{}_{}{}^{}\mathrm{B}$. The photopion reaction predominantly excites $M2\mathrm{}$ states at low $q$ and $M4\mathrm{}$ states at high $q$, with both peaking in the energy region 6-7 MeV in ${}_{}{}^{13}{}_{}{}^{}\mathrm{B}$ (21-22 MeV in ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}$). The results are compared with predicted $M2\mathrm{}$ and $M4\mathrm{}$ relative strength distributions and also with the available data on radiative capture of stopped pions and inelastic electron scattering.

NUCLEAR REACTIONS ${}_{}{}^{13}{}_{}{}^{}\mathrm{C}(\mathrm{e}, {\pi }^{+}){}_{}{}^{13}{}_{}{}^{}\mathrm{B}_{}^{*}{}_{}{}^{}$ ($E_x=0, 3.5, 6.4, \mathrm{and} 9$ MeV), $E_{\mathrm{e}}=195\mathrm{}$ MeV; measured $\sigma \left(\theta \right)$, $\theta =30-150\mathrm{}°$, $\Delta \theta =20\mathrm{}°$. Enriched target. Results compared to theoretical $M2\mathrm{}$ and $M4\mathrm{}$ strength distributions.

• Received 7 March 1983

DOI:https://doi.org/10.1103/PhysRevC.28.464