In-medium mass renormalization of nucleons detected in the axial charges of the beta decays of spin aligned B-12 and N-12

The axial charge of the weak nucleon axial vector current extracted from th e anisotropic beta-ray angular distributions of spin aligned B-12 and N-12 was accounted for mainly in terms of the impulse value y(IA) and the soft p ion exchange effect term Y-exch. The experimental value, y = 4.66 +/- 0.06( stat) +/- 0.13(syst), was enhanced by 63% from the impulse value y(IA) = 2. 85 which includes the core polarization effect. The experimental excess of 0.54 over the theoretical value y(IA) + y(exch) = 4.12 is accounted for by the in-medium mass reduction from the free nucleon value, if there is such an effect, of about (12 +/- 4)% for the nucleons decaying in the A = 12 tri ad.