New values for the ($p, n$) thresholds of ${\mathrm{N}}^{15}$, ${\mathrm{Mg}}^{25}$, ${\mathrm{Mg}}^{26}$, ${\mathrm{Cu}}^{63}$, and ${\mathrm{Cu}}^{65}$ are, in corresponding order, 3776±8, 5289±25, 5200±10, 4213±8, and 2170±5 kev. The value given for ${\mathrm{Mg}}^{26}$ is for the transition to the first excited state in ${\mathrm{Al}}^{26}$. In the process of providing an energy calibration curve for the magnetic analyzer of the Oak Ridge National Laboratory 5.5-Mv Van de Graaff, it was found that the resonances in the ${\mathrm{F}}^{19}(p, \alpha \gamma ){\mathrm{O}}^{16}$ reaction reported by others at 1355 and 1381 kev actually occurred at proton energies of 1347±2 and 1374±2 kev, respectively. Previous measurements on the ($p, n$) thresholds of ${\mathrm{F}}^{19}$, ${\mathrm{Na}}^{23}$, and ${\mathrm{Al}}^{27}$, which were based in part on these resonances as calibration points, have been repeated, giving 4240±8, 5053±10, and 5792±10 kev, respectively.

• Received 9 May 1955

DOI:https://doi.org/10.1103/PhysRev.99.1393