The $Q$ value for the reaction ${\mathrm{B}}^{10}({\mathrm{He}}^3, {\mathrm{N}}^{12})n$ has been measured by observing the ${\left({\mathrm{N}}^{12}\right)}^{5+}$ recoil ions in a magnetic spectrometer at 10-MeV bombarding energy. Observations at 1.7° and 7.0° laboratory angle yield $Q=1.570\mathrm{}\pm 0.025$ MeV, based on the ThC' alpha line at 8.7841 MeV. The ${\mathrm{N}}^{12}$-${\mathrm{C}}^{12}$ mass difference computed from this $Q$ value corresponds to an endpoint energy of 16.320 MeV for the ${\mathrm{N}}^{12}$ beta decay and a $\mathrm{ft}$ value of (1.29±0.02)×${10}^4$. The ratio $\frac{ft\left({\mathrm{N}}^{12}\right)}{ft\left({\mathrm{B}}^{12}\right)}$ becomes 1.10±0.02.

• Received 7 November 1963

DOI:https://doi.org/10.1103/PhysRev.133.B1502