The efficiency of the nuclear reaction ${\mathrm{C}}^{12}(p,\gamma ){\mathrm{N}}^{13}$ has been measured over the energy range from 125 kev to 200 kev, with results which are in good agreement with those recently published by Hall and Fowler. The cross section ranges from 1.0×${10}^{-33\mathrm{}}$ ${\mathrm{cm}}^2$ at 128 kev to 23×${10}^{-33\mathrm{}}$ ${\mathrm{cm}}^2$ at 194 kev. The thick-target yield of the reaction was measured, by detecting the ${\mathrm{N}}^{13}$ positron activity with an absolutely calibrated counter, and the cross sections were obtained by differentiation of the thick-target yield curve.

• Received 14 October 1949

DOI:https://doi.org/10.1103/PhysRev.77.194