C12(γ, n)Yield Curve Near Threshold

The ${\mathrm{C}}^{12}(\gamma , n)$ yield curve has been studied near the threshold for the reaction with a 22-Mev betatron. A discontinuity in slope, or "break," is observed to occur 370 kev above the threshold. This is in disagreement with previously published results. The discrepancy is important since it indicates a disagreement in the measurement of the ${\mathrm{C}}^{12}(\gamma , n){\mathrm{C}}^{11}$ threshold, and this threshold is used to establish the energy calibration of the betatron.