A Method for In Situ Depth Profiles of Alpha and Beta Contaminants in Soil Using Scintillators and Fiber Optic Light Guides

This work examines the potential use of two scintillation detectors for in-situ measurements of alpha and beta particles at various depths in soil. Use of an organic (plastic) scintillator was investigated for beta-particle measurements and a ZnS(Ag) inorganic scintillator was investigated for alpha-particle measurements. Each detector was connected to a photomultiplier tube by varying light-guide lengths of 20 cm, 50 cm, and 100 cm. Soil standards, each containing a known quantity of a single radionuclide, were prepared to characterize the detectors. Efficiency of the alpha and beta detectors ranged from 0.0021 to 0.0041 cps/Bq/g and 0.064 to 0.18 cps/Bq/g, respectively. Detection limits (LD) for a 15 minute count ranged from 0.33 to 1.6 Bq/g and from 8.1 to 15 Bq/g for the beta and alpha detectors, respectively. Resolution in the alpha detector was poor with values ranging from 85 to 150%. Detectors of this type have the potential advantage of providing depthprofile information in situ, but would generally be useful only in their estimation of gross alpha or gross beta activity. * Current address: U.S. Department of Agriculture, Washington, DC