EXCITATION OF E1 AND M2 RESONANCES VIA (PI-,GAMMA) REACTIONS ON O-16,O-18

The photon spectra from the reaction O16(π-,γ)N16 and O18(π-,γ)N18 were measured with a high-resolution pair spectrometer. Transitions to 2- states having T=1 in N16 and T=2 in N18 appear to dominate. Excitation of 1- states in the giant dipole resonance region, which are the analogs of the levels excited in photoabsorption and inelastic electron scattering on O16 and O18, respectively, were also observed. The total and partial branching ratios for bound states and giant-resonance transitions are compared with shell-model predictions. Higher admixtures to the predominantly 1p-1h wave functions are found to be necessary to obtain agreement with the measured branching ratios. A new treatment of the continuum and resonance excitation, based on calculations of Ohtsubo et al., is compared with the data. NUCLEAR REACTIONS Radiative pion capture; measured photon spectra for O16(π-,γ)N16 and O18(π-,γ)N18; deduced transitions and transition strength with Jπ=1-, 2- and T=1 and T=2 respectively; comparison with shell-model calculations. © 1979 The American Physical Society.