The Conservation of Momentum in the Disintegration ofLi8

Apparatus for the introduction of radioactive materials into a cloud chamber has been employed to investigate the conservation of momentum in the $\beta$-decay of ${\mathrm{Li}}^8$ to ${\mathrm{Be}}^8$, which subsequently breaks up into two $\alpha$-particles. The projection on the plane of measurement of the angle between the two $\alpha$-particles is a measure of one component of the recoil momentum of the ${\mathrm{Be}}^8$. Additional information is obtainable from the momentum of the electron but relatively few cases occur where both $\alpha$-particles and the electron are in the plane of the cloud chamber. The ${\mathrm{Li}}^8$ is produced by bombarding with deuterons a thin deposit of LiOH on beryllium or gold foils. The mean squares of the observed momenta relative to the maximum possible momenta were 0.247 (Be foil) and 0.349 (Au foil). Corrected for scattering and other errors these become 0.197±0.025 and 0.207±0.034, respectively, the probable errors quoted being statistical in origin. The weighted mean, rounded off to two figures, is 0.20±0.02. This value is roughly twice that obtained taking into account only the emitted electrons, and approximately equal to that calculated for an electron and neutrino emitted with no preferred angle of ejection between them.