The photon spectra in the capture of stopped pions on ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ and ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$ were measured in the 50-150-MeV region with a high-resolution pair spectrometer. The total radiative capture branching ratios are 2.13±0.21 and 2.27±0.22%, respectively. The spectrum corresponding to the first 13 MeV excitation in each of the residual nuclei ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$ and ${}_{}{}^{10}{}_{}{}^{}\mathrm{Be}$ is dominated by the transition to the analog of a giant $M1\mathrm{}$ state of the target nucleus. The ground state transitions in both nuclei are resolved experimentally. The measured branching ratio for the extremely weak ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$(g.s.) transition is (3±2) × ${10}^{-5\mathrm{}}$. There is evidence for selective excitation of the analogs of the giant dipole spin-isospin states of ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$, of which the $3^{-}$ component appears to be the strongest. In ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$ the transition strength to the giant resonance region is more fragmented. An analysis is presented that employs an impulse-approximation Hamiltonian with amplitudes taken directly from the fundamental process on the nucleon, ${\pi }^{-}+p\to n+\gamma$, and shell-model wave functions obtained using realistic interactions in the $1s$, $1p$, and $2s-1d$ shells. Also, a calculation for the ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}$(g.s.) transition from $1s$ capture using the "elementary-particle soft-pion" ansatz is presented.

NUCLEAR REACTIONS ($\pi , \gamma$) on ${}_{}{}^{10}{}_{}{}^{}\mathrm{B}$ and ${}_{}{}^{14}{}_{}{}^{}\mathrm{N}$ with stopped ${\pi }^{-}$; measured photon spectrum (50-150 MeV) and radiative branching ratio using pair spectrometer of 2 MeV resolution. Shell-model calculations compared with measurements.

• Received 9 September 1974

DOI:https://doi.org/10.1103/PhysRevC.12.921