Techniques are described for observing low energy (15-60 kev) "threshold" neutrons in the presence of fast neutrons. The threshold of the ${\mathrm{T}}^3\mathrm{}(p,n)\mathrm{}{\mathrm{He}}^3$ reaction was found to be 1020.3 kev, which gives a $Q$-value of the reaction equal to - 764.7 kev and a neutron-hydrogen mass difference of 783.2 kev. Interpretation of data near the threshold of the ${\mathrm{Li}}^7\mathrm{}(p,n)\mathrm{}{\mathrm{Be}}^7$ reaction gives indication of a level in ${\mathrm{Be}}^8$ near 18.90 Mev. Three neutron thresholds have been observed in the reaction ${\mathrm{Be}}^9\mathrm{}(d,n)\mathrm{}{}_{}{}^{*}{}_{}{}^{}\mathrm{B}_{}^{10}{}_{}{}^{}$ at deuteron energies of 920, 985, and 1916 kev. The corresponding $Q$-values are -752, -805, and -1566 kev; these give excited states in ${\mathrm{B}}^{10}$ at 5.110, 5.163, and 5.924 Mev. The threshold of the reaction ${\mathrm{O}}^{16}\mathrm{}(d,n)\mathrm{}{\mathrm{F}}^{17}$ was determined to be 1836 kev, giving a $Q$ value of -1631 kev and a mass of ${\mathrm{F}}^{17}$ equal to 17.007506.

• Received 11 June 1951

DOI:https://doi.org/10.1103/PhysRev.83.1091