CsI(Tl) with photodiodes for identifying subsurface radionuclide contamination

A cylindrical (15/spl times/61 mm) CsI(Tl) scintillation detector with two side-mounted photodiodes has been developed to collect spectral gamma-ray data in subsurface contaminated formations at the US Department of Energy's Hanford Site. It operates inside small-diameter, thick-wall steel pipes pushed into the ground to depths up to 20 m by a cone penetrometer system. The detector provides a rugged, efficient, magnetic-field-insensitive means for identifying gamma-ray-emitting contaminants (mainly /sup 137/Cs and /sup 60/Co). Mounting two 3/spl times/30-mm photodiodes end-to-end on a flat area along the detector's side provides efficient light collection over the length of the detector.<>