Nuclear critical opalescence and the M1 form factors of 12C and 13C

It is shown that core polarization by the nuclear pion field has opposite effects on the M1 form factors of 12C(15.11 MeV) and 13C(g.s.). New data on 13C are found to agree with this prediction and a common interpretation of the experiments is shown to be possible for the two nuclei in terms of critical opalescence. Discrimination from alternative explanations of the observed anomalies should await further experiments, especially photopion reactions. (orig.)