In situ, high sensitivity, measurement of 90strontium in ground water using Cherenkov light

The measurement of 90Sr in soils and ground water is important for characterization and remediation of radioactively contaminated sites. Measuring the 90Sr content to a few pCi/g of soil has been accomplished based on a design of scintillating fibers in a multilayered configuration measuring the high-energy beta emitted from 90Y decay (when in secular equilibrium with 90Sr), but has not been applied to water because the technique is sensitive to only the first few mm of soil. The volume of the source to which the detector is sensitive limits the theoretical sensitivity of such a detector, unless chemical preprocessing to strip the 90Sr from the water is performed. 90Sr activity in water can be quantified by detecting the high-energy beta particle by the Cherenkov light it produces when the high-energy beta from 90Y passes through the medium. We have used this phenomenon to sensitively measure 90Sr (90Y) from a volume of water large enough (765 cm3) to make very sensitive measurements with short count times. For counting intervals of about 1000 s, we were able to achieve a minimum detectable concentration (MDC) (at 4.65σ above background) of 14 pCi/L, and for 3000 s counts the MDC dropped to the drinking water limit of 8 pCi/L.