Studies on the isomeric pair, Nb^89m and Nb⁸⁹

Abstract

By bombardment of zirconium, niobium, yttrium, and silver targets in the 184-inch cyclotron it has been possible to produce the isomer pair Nb^89m and Nb⁸⁹. The isomerism arises from the odd 41st proton below the 50-proton closed shell of the single-particle nuclear model. Nb⁸⁹(g_9/2) is a 1.9-hour activity emitting 2.85-Mev positrons to produce Zr⁸⁹. The yield of the Nb^89m(p_½) is about 30-100 fold less and its radiations were not directly observed. By scintillation spectrometer measurements on zirconium daughter activity it is shown that Nb^89m decays with about a 2-hour half-life to 4.4-minute Zr^89m(p_½). The M4 gamma transition between the two niobium levels is not observed, indicating that the level spacing is small and the upper level deactivates primarily by positron emission. The logft values are larger than expected and are discussed in terms of the even-even core rearrangement considerations of A. De-Shalit and M. Goldhaber [Phys. Rev. 92, 1211 (1953)]. Nb⁸⁹ was also prepared by bombardment of NaBr with accelerated carbon ions in the 60-inch cyclotron.