The SD78W, sodium iodide (NaI) well scintillator in primarily used for gamma ray assay and wipe test analysis. The SD78W is a positive high voltage detector employing a 1.75 in. x 2 in. (44.5 mm x 50.8 mm – diameter x thickness) NaI(Tl) cylindrical scintillation crystal with a 0.7 in. x 1.5 in (17.8 mm x 38.1 mm) well.