Delta-isobar configurations in 12C and 16O nuclei

The differential yield of the reaction O-16(gamma, pi (+) p) at the maximum photon energy of 450 MeV was measured in the region of high momentum transfers to the residual nuclear system. The experimental results obtained for the O-16 nucleus and the cross section measured earlier for the reaction C-12(gamma, pi (+) p) were analyzed on the basis of a model that takes into account the admixture of isobar states in the nuclear wave function. The probabilities for the delta-isobar configurations in the ground states of the carbon and oxygen nuclei per nucleon were estimated empirically at 0.012 +/- 0.003 +/- 0.002 and 0.019 +/- 0.003 +/- 0.003, respectively.