The electron-neutrino angular correlation coefficient $\alpha$ has been determined in the beta decay of ${\mathrm{Ne}}^{19}$ by observing the spectrum of positrons coincident with nuclear recoils emitted approximately antiparallel to the positrons. The source region in the volume containing the ${\mathrm{Ne}}^{19}$ activity was defined by a retarding grid system and by the requirement that coincident recoils from the source exhibit the correct delay relative to the positrons. Negatively charged recoils were detected in a silver-magnesium alloy electron multiplier, which was also found to be fairly sensitive to uncharged recoils in the energy range below two hundred electron volts. Positron energies were determined with a crystal-photomultiplier spectrometer and multichannel analyzer. Comparison of the measurements with calculated spectra yields a value of $\alpha =-0.15\mathrm{}\pm 0.2$, confirming earlier conclusions that the beta interactions has the form $\mathrm{ST}\left(P\right)\mathrm{}$ rather than $\mathrm{VT}\left(P\right)\mathrm{}$.

Earlier measurements on the recoil spectrum using this apparatus had given $\alpha =-0.8\mathrm{}\pm 0.4$. The difference between this value and the present measurements was found to be due to uncertainties in circuit timing which have small effects on the electron spectrum but much larger effects on the spectrum of recoils.

• Received 11 October 1956

DOI:https://doi.org/10.1103/PhysRev.105.673