The coefficient $\alpha$ in the electron-neutrino angular correlation $W\left(\phi \right)=[1+\alpha (\frac{p}{W}\left)cos\phi \right]$ for the ${\mathrm{He}}^6$-${\mathrm{Li}}^6$ transition has been determined by measuring the coincidence rate between recoil ions and beta rays of selected energy as a function of the angle between the particles. Since the decay of ${\mathrm{He}}^6$ (allowed $\mathrm{ft}$ value and $\Delta I=1\mathrm{}$) obeys only Gamow-Teller selection rules, the interaction Hamiltonian for this transition is specified completely by ($G_{A}A+G_{T}T$). The measured values of the correlation coefficient are ${\alpha }_{1.25}=+0.36\mathrm{}\pm 0.11$ for beta rays with mean energy 1.25 Mev and ${\alpha }_{2.0}=+0.31\mathrm{}\pm 0.14$ for the mean energy 2.0 Mev. These results are compared with ${\alpha }_T=+\frac{1}{3}$ and ${\alpha }_A=-\frac{1}{3}$ predicted from the pure tensor and axial vector invariants, respectively. The limiting value set by the experiment for ($\frac{G_A}{G_T}$) together with the observed absence of the Fierz interference terms for allowed beta spectra proves that the tensor invariant is dominant in the beta-decay interaction of ${\mathrm{He}}^6$.

• Received 9 November 1954

DOI:https://doi.org/10.1103/PhysRev.97.991