A thin target of magnesium oxide enriched in ${\mathrm{Mg}}^{24}$ was bombarded by 5.52-Mev ${\mathrm{He}}^3$ particles. The outgoing neutrons were measured by the method of proton recoils in photographic emulsions. The ground-state $Q$ value of the ${\mathrm{O}}^{16}({\mathrm{He}}^3, n){\mathrm{Ne}}^{18}$ reaction is determined in this experiment to be -3.19±0.04 Mev. The $Q$ value of the ${\mathrm{Mg}}^{24}({\mathrm{He}}^3, n){\mathrm{Si}}^{26}$ ground-state reaction is 0.08±0.08 Mev. The mass of ${\mathrm{Si}}^{26}$ is then 25.99232±0.00007 amu (${\mathrm{C}}^{12}$ standard). In addition, excited states of ${\mathrm{Si}}^{26}$ at 1.78±0.06 and 2.79±0.08 Mev have been observed. Angular distributions of these four neutron groups and of the ${\mathrm{C}}^{12}({\mathrm{He}}^3, n){\mathrm{O}}^{14}$ ground-state group are also reported: in all but one case, the distributions are peaked in the forward direction.

• Received 25 April 1960

DOI:https://doi.org/10.1103/PhysRev.119.1681