Decay ofRb90

Following the neutron irradiation of uranyl stearate, ${\mathrm{Rb}}^{90}$ sources were prepared by milking from the emanated ${\mathrm{Kr}}^{90}$. The decay properties of ${\mathrm{Rb}}^{90}$ were then investigated with scintillation techniques. From single-crystal and gamma-gamma coincidence spectra, gamma rays (and intensities) were found at energies of 0.53(6.6), 0.72(6.5), 0.832(90), 0.86(10), 1.03(6.0), 1.11(13), 1.24(4.3), 1.40(8.3), 1.70(6.1), 1.82(4.8), 2.20(3.6), 2.51(5.6), 2.72(1.8), 2.84(3.0), 3.07(9.7), 3.34(28), 3.54(12), 4.13(20), 4.34(24), 4.37(7.8), 4.60(8.4), 5.08(3.0), and 5.23(6.7) MeV. Also, from single-crystal and beta-gamma coincidence spectra, beta-ray groups were observed with energies of 1.31, 2.0, 2.2 (complex), 4.37, 5.81, and 6.60 MeV, where the last group represents the separation between the ${\mathrm{Rb}}^{90}$-${\mathrm{Sr}}^{90}$ ground states. The decay scheme proposed for ${\mathrm{Rb}}^{90}$ involves levels in ${\mathrm{Sr}}^{90}$ at 0.832, 1.69, 1.94, 2.23, 3.07, 3.34, 4.15, 4.34, 4.60, 5.08, and 5.23 MeV. The half-lives of ${\mathrm{Rb}}^{90}$ and ${\mathrm{Rb}}^{91}$ have been remeasured as 2.91±0.05 min and 1.17±0.10 min, respectively.