Gamma-Rays Emitted During the Radioactive Transitions ${\mathrm{Sb}}^{124}$→${\mathrm{Te}}^{124}$ and ${\mathrm{Na}}^{24}$→${\mathrm{Mg}}^{24}$

Pair electrons observed in a cloud chamber provide the most accurate means of measuring gamma-ray energies, provided suitably rigid criteria of the selection of valid pairs are followed. The gamma-ray energies here reported were deduced from stereoscopic photographs of pair electrons formed in the gas of a cloud chamber. The magnetic field was known in absolute value to 1 percent or less and in relative value was constant to 0.2 percent or less. The radius of the electron tracks was measured by a special measuring engine. Careful collimation between the source and the cloud chamber was found necessary. ${\mathrm{Sb}}^{124}\to {\mathrm{Te}}^{124}$