A new 1.9±0.3-hour activity was found in niobium fractions isolated from proton irradiated niobium and zirconium metal foils. By identification of the 78-hour daughter activity, the mass assignment has been made to ${\mathrm{Nb}}^{89}$. Evidence indicates that the decay is a simple positron emission of 2.9±0.4 Mev maximum energy. Evidence was also obtained for the existence of the ½ - isomeric state in ${\mathrm{Nb}}^{89}$ which decays with a 0.8±0.3-hour half-life by positron emission to the similar 4.4-minute state in ${\mathrm{Zr}}^{89}$.

• Received 1 April 1954

DOI:https://doi.org/10.1103/PhysRev.95.410