Radiations ofMo90and the Isomeric States ofNb90

Gamma-gamma coincidence measurements of the radiations of 5.7-hour ${\mathrm{Mo}}^{90}$ showed that the 120- and 250-kev gamma rays previously reported by Diamond were delayed. Further experiments showed the existence of a 24-second isomer of ${\mathrm{Nb}}^{90}$ emitting 120-kev gamma rays and a 10 to 20 millisecond isomer emitting 250-kev gamma rays. The transition types were not assigned unambiguously but the 24-second isomer is probably $E2\mathrm{}$ and the 10 to 20 millisecond isomer $E3\mathrm{}$ or $M3\mathrm{}$ in nature.