Changes in the decay constant of the isomer ${\mathrm{Nb}}^{90m}$ were measured. We found that $\frac{({\lambda }_{\mathrm{Nb}\left(\mathrm{fluoride}\mathrm{complex}\right)\mathrm{}}-{\lambda }_{\mathrm{Nb}})}{{\lambda }_{\mathrm{Nb}}}=(-3.9\mathrm{}\pm 0.8)\times {10}^{-2\mathrm{}}$, $\frac{({\lambda }_{{\mathrm{Nb}}_2{\mathrm{O}}_5}-{\lambda }_{\mathrm{Nb}})}{{\lambda }_{\mathrm{Nb}}}=(-1.9\mathrm{}\pm 0.5)\times {10}^{-2\mathrm{}}$. The Nb (fluoride complex) result confirms the value previously obtained by Cooper et al., which had been questioned because of the negative result obtained by Weirauch et al. in a similar measurement. Some possible causes of this high sensitivity to chemical environment are discussed.

• Received 30 October 1969

DOI:https://doi.org/10.1103/PhysRevC.1.1114