RAPID-DETERMINATION OF SR-90 BY COMPTON SUPPRESSION GAMMA-RAY SPECTROMETRY

This work presents a low-level background gamma spectrometry system ca pable of achieving rapid determination of Sr-90 without chemical separ ation, in a soil sample when the Sr-90 to gamma-ray emitting nuclide c oncentration ratio exceeds 10. The system consists of a highly efficie nt HPGe central detector operated in coincidence or anticoincidence wi th a NaI(Tl) guard detector and a NaI(Tl) backscatter detector Experim ental results indicate that the bremsstrahlung radiation from a pure b eta-emitter can be distinguished with respect to the differences in no rmal and coincidence spectra. The Sr-90 activity can be directly deter mined in the sample in less than 1 hour with a minimum detectable conc entration (MDC) estimated at 0.002 Bq . g(-1) for a sample containing no appreciable gamma-ray nuclides or other high energy, beta-emitting nuclides. In actual measurement, a 0.06 Bq . g(-1) MDC for contaminate d soils is achieved.