Selected Citation
Electron-Neutrino Angular Correlation in the Decay of He6
The energy spectra of recoil lithium ions in coincidence with beta particles of selected energy have been measured for the beta decay of He6. The beta-particle energy was determined with a well-type beta scintillation detector; and the energy and charge of the recoil ions were measured with an electrostatic spectrometer and time-of-flight analyzer. The electron-neutrino angular-correlation coeKcient determined from the observed energy distributions of recoil ions is ) = — 0. 319&0.028. The ratio of the tensor to axial vector coupling constants calculated from this measurement is (~ Cr )'+ Cr'~')/(~ Cz ['+ Cg'[') =0022&0044. A new measurement of the Hee beta spectrum was made with a thin-lens magnetic spectrometer, and the maximum energy is 3. 508&0. 015 MeV.
The measurement of the electron-neutrino angular correlation in allowed beta transitions is one of the methods by which experimental evidence may be obtained on the form of the beta-decay interaction. Because He' is the only known monatomic gas which decays by a simple superallowed Gamow-Teller transition, this isotope has been used in several different types of electron-neutrino angular correlation experiments to determine the ratio of the tensor to axial vector coupling constants. The results of these measurements, however, have not all been consistent. After parity violation was demonstrated in the weak interactions, many new experiments were performed to obtain information on the new coupling constants which had to be introduced into the beta-decay interaction. " The results of these experiments and of a measurement" of the electron-neutrino angular correlation in the decay of Ar35 were in disagreement with certain previous angular correlation experiments. Reevaluation of one of the principal measurements on He revealed serious instrumental discrimination, and several investigations were started to remeasure this correlation coefficient.
The experiment described in this paper was undertaken at that time to redetermine the He6 electron-neutrino angular correlation by a new method, which is not subject to the instrumental effects found in the previous measurements and which is more sensitive to the value of the angular correlation obtained on the form of the beta-decay interaction.