Isovector radiative decays and second-class currents in mass 8 nuclei

The total isovector M1 radiative width of the 16.6-16.9 MeV doublet in 8Be to the broad first excited state has been measured via the 4He(α,γ) reaction to be 6.10 +- 0.53 eV. Angular distributions at the 16.6 and 16.9 MeV resonances have been measured and determine the isovector E2 to isovector M1 mixing ratio to be delta[(E2,T = 1)/(M1,T = 1)] = 0.19 +- 0.03. A comparison of these results with recent β-α angular correlation measurements of 8Li and 8B is consistent with predictions of the conserved vector current theory and the absence of a second-class induced tensor form factor