Interference of 91Y with the rapid determination of 90Sr originating from the Chernobyl fallout debris

An improved method for the determination of 90Sr and 91 in grass ashes and other materials was developed, based on a tributylphosphate (TBP) extraction of the radio-yttrium. The interference of 91Y with the β-measurement of the extracted 90Y was studied and eliminated either by graphic subtraction of the 91Y decay diagram from the total decay plot of the yttrium fraction or by energy discrimination of these two nuclides by Cerenkov-counting. Using the latter method, the analysis of one sample of ash takes six hours. Results of 90Sr and 91Y acivity concentrations in grass samples collected after the Chernobyl event and of 90Sr in various IAEA reference materials are given. (orig.)