Measurement of ³²P in wet-ashed plant samples utilizing Cherenkov radiation

The radiometric assay of 32P in plant material by means of ?erenkov counting was investigated. Plant material was ashed with nitric and perchloric acids and any colour remaining in the solutions could easily be removed with activated charcoal. Measurements were done in an automaticliquid scintillation counter using either a wide-window discriminator setting including the whole 32P ?erenkov spectrum or a 5% window combined with balance-point operation. The efficiency of the latter method was 25% compared to 41% with the wide-window. However, balance-point operation is preferred because it was less affected by quenching agents and up to 3g samples could be counted without change in efficiency. By using a quenched 90Sr- e 0Y reference source any deviations in instrumental settings could easily be detected.