Rapid determination of strontium radionuclides in plants, fodder and foodstuffs

摘要

The fission yield, the transfer factors in the food chain and the dose coefficient are large for the nuclear fission product Sr-90. The surveillance of Sr-90 in the food chain is therefore important in precautionary radiation protection and in assessing the radiation dose to the public especially after a nuclear incident. Prior to analysis, as it is a pure β-emitter, Sr must be separated from the sample by procedures which, for complex organic samples, are lengthy, laborious and dependent on operator skill. Ubiquitous natural radionuclides and short-lived fission products in samples contaminated with fresh fallout may interfere. Here we describe a fast, reproducible and effficient method for extracting Sr from grass, clover, maize, wholemeal rye, baby food, and total diet. The method depends on obtaining an ash free of traces of organic interferences. Sr may be separated from a dilute nitric acid leachate of such ash with a solution of dicyclohexyl-18-crown-6 in chloroform. Interfering radionuclides are removed with a special manganese (IV) oxide (active, precipitated from Merck). Sr is precipitated as carbonate then dispersed in a cocktail for liquid scintillation spectrometry. This allows simultaneous counting of Sr-89 (a short-lived β-emitter in fresh fallout) and Sr-90. The chemical yields of Sr determined with the gamma-emitting Sr-85 tracer are reproducible and greater than 75 % in all cases. The sample ashing requires 18 h and the extraction 4.0 to 4.5 h. Thus, a duplicate analysis may be completed within 2 days of receipt of the sample.