The Disintegration ofSr91andY91m

Abstract

The radiations from the fission product ${\mathrm{Sr}}^{91}$ (9.67-hr) and its daughter isomer ${\mathrm{Y}}^{91m}$ (50.3-min) have been studied using a magnetic lens spectrometer, a high resolution 180° focusing spectrometer, and a scintillation spectrometer. Coincidence measurements were made to check on certain genetic aspects of the decay scheme. Five beta-ray groups are observed with end-point energies and relative intensities of 2.665 Mev, 26.4 percent; 2.03 Mev, 4.1 percent; 1.359 Mev, 29.2 percent; 1.093 Mev, 33.1 percent; and 0.62 Mev, 7.2 percent. The 2.665-Mev group has a shape characteristic of a once forbidden transition involving a spin change of 2 units. Gamma-rays are found with energies of 1.413, 1.025, 0.93, 0.748, 0.645, and 0.5512 Mev. The 50.3-min isomeric level in ${\mathrm{Y}}^{91}$ decays only by gamma-emission to the ground state. The 0.5512-Mev gamma-ray associated with this transition has a $\frac{K}{\mathrm{}(L+M)\mathrm{}}$ internal conversion ratio of 6.00, which is consistent with an $M4\mathrm{}$ assignment. A disintegration scheme is proposed.