Convert CPM units to DPM units
In order to convert CPM units to DPM units, laboratory staff must use the following equation:
DPM = CPMsample – CPMbackground/Detector Efficiency
Calculate the detector efficiency
In order to calculate the detector efficiency, laboratory staff must use the following equation:
Detector Efficiency = CPMstandard count/DPMstandard
Units for detector efficiency calculation are determined by measuring detection sensitivity with a source of known activity and by obtaining the DPM unit listed for the source being used (beta or gamma).
Additionally, lab staff should note calculated detector efficiency and proper instrument settings in laboratory radiation contamination survey files.