Measurement of the Mass ofHe5

A $Q$ value of 15.15±0.04 Mev for the reaction ${\mathrm{Li}}^6(t, \alpha ){\mathrm{He}}^5$ has been obtained through a measurement of the energy of the alpha particles. The mass of ${\mathrm{He}}^5$ is then 5.01390±0.00004 amu or ${\mathrm{He}}^5\to {\mathrm{He}}^4+n+0.97\mathrm{}\pm 0.04$ Mev. The width of the ground state is 0.7±0.2 Mev.