The radiations of ${\mathrm{Mo}}^{99}$ and ${\mathrm{Tc}}^{99m}$ have been reinvestigated by means of scintillation spectroscopy. Employing single-channel pulse-height analyzers in coincidence, it has been established that a triple cascade of gamma rays, 741 kev→41 kev→140 kev occurs. The 741-kev radiation is also coincident with a gamma ray at 181 kev by an alternate branch of de-excitation which is equally probable. Radiation at 780 kev is present but is non-coincident with other gamma rays. From these data, a disintegration scheme can be constructed. A gamma ray of energy 372 kev was also detected, and, although it appeared to have the proper half-period to be associated with ${\mathrm{Mo}}^{99}$, was found to be not in immediate coincidence with beta rays or other gamma rays, suggesting that it might be related to an impurity.

• Received 16 November 1953

DOI:https://doi.org/10.1103/PhysRev.94.91