The coefficients ${\alpha }_{\mp }$ in the alignment-correlation terms $\mathcal{a}{\alpha }_{\mp }E{P}_2\left(cos\theta \right)$, in ${}_{}{}^{12}{}_{}{}^{}\mathrm{B}$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{N}$ decays have been determined; ${\alpha }_{-}\left({}_{}{}^{12}{}_{}{}^{}\mathrm{B}\right)=+(0.006\mathrm{}\pm 0.018)\%/\mathrm{MeV}$ and ${\alpha }_{+}\left({}_{}{}^{12}{}_{}{}^{}\mathrm{N}\right)=-(0.273\mathrm{}\pm 0.041)\%/\mathrm{MeV}$. The sign of ${\alpha }_{+}\left({}_{}{}^{12}{}_{}{}^{}\mathrm{N}\right)$ was determined for the first time, by use of an NMR method and measurements on $\beta -\gamma$ correlation in aligned ${}_{}{}^{12}{}_{}{}^{}\mathrm{N}$. The ${\alpha }_{-}-{\alpha }_{+}$ result is consistent with strong conservation of vector currents without second-class currents and the ${\alpha }_{-}+{\alpha }_{+}$ result gives unique information on the time component of the axial-vector current.

• Received 2 July 1979

DOI:https://doi.org/10.1103/PhysRevLett.43.1083