Beta spectrum of 87Kr

A measurement of the β spectrum of ⁸⁷Kr was undertaken to resolve some discrepancies in recently reported values of the branching of the β decay to the ground state of ⁸⁷Rb. Sources of mass-separated ⁸⁷Kr, provided by the TRISTAN on-line isotope separator, were investigated with a high-resolution $\pi \sqrt{2}$ magnetic spectrometer. Using constraints based on previous γ-ray decay schemes, the measurement yielded a Q value of 3.888 ± 0.007 MeV and a ground-state β intensity of (30.5 ± 2.2)%. In addition, the intensity ratio for an unresolved γ-ray doublet at 2555 keV was independently determined on the basis of β-branch intensities to the levels at 2555 and 2960 keV.