M1Decay Rates and Second-Class Currents in Mass 8

The total isovector $M1\mathrm{}$ $\gamma$-decay rate of the 16.6-16.9-MeV doublet in ${}_{}{}^8{}_{}{}^{}\mathrm{Be}$ to the broad first excited state has been measured with the reaction ${}_{}{}^4{}_{}{}^{}\mathrm{He}({}_{}{}^4{}_{}{}^{}\mathrm{He}, \gamma )$. A width of 4.8 ± 0.7 eV has been found. When properly interpreted, this result seems consistent with predictions of conserved vector currect theory and with the absence of a second-class induced-tensor form factor.