1.57-MeV State inMo94

In an attempt to make an unambiguous spin assignment to the 1.57-MeV state in ${\mathrm{Mo}}^{94}$, the gamma radiation following the decay of 20 000-yr ${\mathrm{Nb}}^{94}$ and 6.6-min ${\mathrm{Nb}}^{94m}$ has been studied. In the decay of the former activity, an upper limit of ≅0.03% has been placed on the intensity of a 1.57-MeV crossover transition relative to that of the cascade transition. This was obtained from a comparison of calculations of the coincidence summing effect in NaI(Tl) crystals with the observed variation of the intensity of the 1.57-MeV peak with source-detector distance. It has been found that approximately 0.2% of the decays of the 6.6-min state in ${\mathrm{Nb}}^{94}$ are by beta emission to the 872-keV state in ${\mathrm{Mo}}^{94}$. Evidence for the existence of a beta branch from the 6.6-min state in ${\mathrm{Nb}}^{94}$ to the 1.57-MeV state in ${\mathrm{Mo}}^{94}$ is presented. The intensity of this branch, relative to that feeding the 872-keV state, is approximately 1%. The directional correlation of the 703-872-keV gamma-ray cascade de-exciting the 1.57-MeV state has been measured. The results of this measurement are consistent with a spin-4 assignment to this state, or a spin-2 assignment with $\delta \approx -0.2\mathrm{}$ for the 703-keV transition. Arguments favoring the former assignment are presented. On the basis of a spin-4 assignment, consistent spins are assigned to the two states in ${\mathrm{Nb}}^{94}$. Several possible configurations for the low-lying states in ${\mathrm{Nb}}^{94}$ are briefly discussed.