The spectral shapes of the ${}_{}{}^{12}{}_{}{}^{}\mathrm{B}$ and ${}_{}{}^{12}{}_{}{}^{}\mathrm{N}$ beta decays have been measured with a beta spectrograph specifically designed to examine the spectral effect of weak magnetism. Writing the weak magnetism correction to the beta spectra as (1+${\mathrm{\alpha }}_{\pm }$E) we find the difference ${\mathrm{\alpha }}_{\mathrm{-}}$-${\mathrm{\alpha }}_{+}$=(1.24±0.42)%/MeV, in agreement with the conserved vector current prediction.

• Received 25 September 1989

DOI:https://doi.org/10.1103/PhysRevC.41.1719