The decay asymmetries ($\mathcal{a}$) in polarized ${}_{}{}^{12}{}_{}{}^{}\mathrm{B}$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{N}$ have been measured as a function of $\beta$-ray energy ($E$). The coefficients ${\alpha }_{\mp }$, in a form of $\mathcal{a}=\mp P\left(\frac{p}{E}\right)(1+{\alpha }_{\mp }E)$, have been determined to be ${\alpha }_{-}\left({}_{}{}^{12}{}_{}{}^{}\mathrm{B}\right)=+(0.31\mathrm{}\pm 0.06)\%/\mathrm{MeV}$ and ${\alpha }_{+}\left({}_{}{}^{12}{}_{}{}^{}\mathrm{N}\right)=-(0.21\mathrm{}\pm 0.07)\%/\mathrm{MeV}$. The experimental value, ${\alpha }_{-}-{\alpha }_{+}=(0.52\mathrm{}\pm 0.09)\%/\mathrm{MeV}$. is larger than the prediction of conserved-vector-current theory, ${({\alpha }_{-}-{\alpha }_{+})}_{\mathrm{CVC}}\simeq 0.27\%/\mathrm{MeV}$, and in favor of the existence of the second-class induced-tensor current.

• Received 18 March 1975

DOI:https://doi.org/10.1103/PhysRevLett.34.1533