Branching fraction in the radioactive decay of /sup 85m/Kr

The branching fraction in the decay of the fission product /sup 85m/Kr to the ground state /sup 85/Kr (10.75 y) was measured relative to the total decay to both /sup 85/Kr and /sup 85/Rb. Samples of /sup 235/U were highly irradiated in a high-flux reactor and dissolved. The /sup 85/Rb was measured by isotope-dilution mass spectrometry, and the /sup 85/Kr was counted in GM tubes the counting efficiencies of which were calibrated with a standardized /sup 85/Kr gas of known disintegration rate. The branching fraction measured with both a low-burnup sample and a high-burnup sample was 0.2160 +- 0.0019, the largest error arising from the uncertainty in the caibration of the standardized gas. 1 figure, 9 tables