Decay ofY92andNb92

Abstract

The radiations of ${}_{39}{}^{}{}_{}{}^{}\mathrm{Y}_{}^{92}{}_{}{}^{}$ (3.50 h) and ${}_{41}{}^{}{}_{}{}^{}\mathrm{Nb}_{}^{92}{}_{}{}^{}$ (10.1 day) have been studied with the help of scintillation spectrometers and a solenoidal beta spectrometer. Analysis of the experimental results indicates that the ${\mathrm{Y}}^{92}$ decay scheme involves six excited states of ${}_{40}{}^{}{}_{}{}^{}\mathrm{Zr}_{}^{92}{}_{}{}^{}$, which have the following energies (MeV), spins, and parities: 0.932 (2+), 1.380 (0+), 1.492 (4+), 1.836 (2+), 2.05 (2+), and 2.33 (3-). The spectrum of the 3.64-MeV beta transition from ${\mathrm{Y}}^{92}$ to the ${\mathrm{Zr}}^{92}$ ground state has a unique first-forbidden shape, identifying ${\mathrm{Y}}^{92}$ as a 2- state. ${\mathrm{Nb}}^{92}$, which decays only to the 1.836- and 0.932-MeV levels of ${\mathrm{Zr}}^{92}$, is postulated to have spin and parity 2+. Several features of the level structure of ${\mathrm{Zr}}^{92}$ appear to be manifestations of simple shell-model phenomena. It is proposed that the main components of the 1.380- and 1.836-MeV states are excited proton configurations, whereas the dominant components of the levels at 0.932, 1.492, and 2.05 MeV are excited neutron configurations.