CHARACTERIZATION AND CALIBRATION OF A LARGE-AREA BETA-SCINTILLATION DETECTOR FOR DETERMINATION OF SR-90

A large area beta scintillation detector has been developed which is c urrently capable of determining Sr-90/Y-90 contamination in surficial soils. The detector system employs scintillating fiber optic arrays, w ith active dimensions approximately 15 cm wide by 100 an long, both en ds of which are coupled to multiple photomultiplier tubes (PMTs). Elec tronic processing includes coincidence requirements to optimize sensit ivity and selectivity for the 2.28 MeV (maximum) beta particle from Y- 90. Low energy beta particles and gamma rays are discriminated against using double ended and multi-layer coincidence requirements. The dete ctor system is personal-computer-software controlled and data restored in a format compatible with standard database software for ease of fi nal data reduction. Experimental calibration studies have shown a line ar response for Sr-90/Y-90 soil concentrations from 12 to over 500 pCi /g and a discrimination factor of 50 to 1 versus Cs-137.