The neutron spectrum from the ${\mathrm{B}}^{10}({\mathrm{He}}^3, n){\mathrm{N}}^{12}$ reaction has been studied at $\overline{E}\left({\mathrm{He}}^3\right)=2.54\mathrm{} \mathrm{and} 3.60$ Mev by the method of proton recoils in nuclear emulsions. The $Q$ value of the ${\mathrm{B}}^{10}({\mathrm{He}}^3, n){\mathrm{N}}^{12}$ reaction has been measured to be 1.46±0.06 Mev. The mass of ${\mathrm{N}}^{12}$ is then 12.02255±0.00007 amu. The data also indicate excited states of ${}_7{}^{}{}_{}{}^{}\mathrm{N}_{}^{12}{}_{}{}^{}$ at 1.06±0.08, 1.56±0.08, (1.97±0.10), 2.35±0.08, 3.18±0.15, and 3.46±0.15 Mev, in good agreement with the known levels of the mirror nucleus, ${}_5{}^{}{}_{}{}^{}\mathrm{B}_{}^{12}{}_{}{}^{}$. At $\overline{E}\left({\mathrm{He}}^3\right)=2.54\mathrm{}$ Mev, the angular distribution of the ground state neutrons is isotropic within statistics in the center-of-mass system, while at $\overline{E}\left({\mathrm{He}}^3\right)=3.60\mathrm{}$ Mev, the angular distribution is peaked forward: $\frac{I\left(0\mathrm{}°\right)}{I\left(140\mathrm{}°\right)}=2.9\mathrm{}\pm 0.7$, in the center-of-mass system.

• Received 15 August 1957

DOI:https://doi.org/10.1103/PhysRev.108.1284