Threshold proton energies for neutron emission have been determined carefully for ${\mathrm{Be}}^9$, ${\mathrm{B}}^{11}$, ${\mathrm{C}}^{13}$, ${\mathrm{O}}^{18}$, ${\mathrm{Cl}}^{37}$, ${\mathrm{K}}^{41}$, ${\mathrm{V}}^{51}$, ${\mathrm{Mn}}^{55}$. Thin target yield data up to about 4 Mev proton energy are reported for ${\mathrm{Be}}^9$, ${\mathrm{B}}^{11}$, ${\mathrm{O}}^{18}$, and ${\mathrm{K}}^{41}$. A summary of all reported $p-n$ thresholds for $Z\le 25$ is included. Isobaric mass differences from $p-n$ measurements and from beta-ray end points are compared. Data concerning the suitability of various $p-n$ reactions as controlled energy neutron sources are included.

• Received 10 July 1950

DOI:https://doi.org/10.1103/PhysRev.80.524