Comparison of the Nuclear-Reaction Energy Scale with the Gamma-Ray Energy Scale

The excitation energy of the first excited state of ${}_{}{}^{24}{}_{}{}^{}\mathrm{Mg}$ was measured with inelastic deuteron scattering using the energy of $\alpha$ particles from ${}_{}{}^{210}{}_{}{}^{}\mathrm{Po}$ as a standard. The result is 1368.2 ± 0.5 keV. The average of recent measurements of the energy of $\gamma$ rays emitted by this state gives an excitation energy of 1368.67 keV based on the electron rest-mass energy. Thus the widely used polonium calibration energy is found to be consistent with the $\gamma$-ray energy standard to within 0.04%.