An Accurate Measurement of the Energy Released in the Disintegration ofLi6by Protons

The energy release in the reaction ${\mathrm{Li}}^6(p,\alpha ){\mathrm{He}}^3$ has been determined by a comparison of the ${\mathrm{He}}^4$ range with that of the alpha-particles from ${\mathrm{Be}}^9(p,\alpha ){\mathrm{Li}}^6$. The energy of the latter reaction is accurately known from electrostatic deflection measurements. The determination was carried out in a small, variable air pressure, absorption cell and ionization chamber, both being at the same pressure. The device had high dispersion, 1 mm of range corresponding to about 13 cm Hg. Calibration of the cell was carried out by a method which utilized this high dispersion. The $Q$ value for the reaction was found to be 3.945±0.06 Mev as compared to the previously accepted value due to Neuert of 3.72±0.08. With the new $Q$ value, ${\mathrm{H}}^3$ is found to be unstable against $\beta$-decay by either 0.19±0.09 or 0.10±0.1 Mev depending on whether Bainbridge's or Aston's value for the deuterium-helium bracket is used. The mass of ${\mathrm{He}}^3$ is found to be 3.01688±0.00011 mass units.