Microscopic and phenomenological parameters of isobaric analog resonances

Two methods have been compared for calculating the S matrix for proton elastic scattering in the IAS range: the method of solving the Lein equations with an optical potential and the reduced width method of the shell model (R matrix theory). The successful application of the former is due to the existence of weak coupling of inelastic channels with an elastic one. From the calculations it follows that about a half of the absorption magnitude in the elastic channel is caused by the effects of violation of the purity of the isospin of IAS in the ''internal'' region. According to the shell-model calculation the isospin purity violation is quite significant, amounting to about 32 per cent. The marked discrepancy observed in the widths has also been noted previously