Precision Radiation Instruments. Inc. MODEL 121 INSTRUCTION MANUAL

Model 121 is a Geiger counter with three probes: Type A probe contains a thin mica end-window Geiger tube, used for detection of alpha and beta particles; Type B probe is used for detection of beta and gamma radiation in general prospecting, and has a sliding shield over the side window for exclusion of beta particles; Type D probe is a sealed probe, with a long cable, for examination of drill-holes up to 1,000 feet in depth.

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