Performance of surface contamination monitors in alpha and beta radiation fields

Radioactive surface contamination consists of unwanted radioactive material deposited in an uncontrolled manner in or on animate or inanimate objects, irrespective of their situations, in such concentrations that either an operational inconvenience or a radiological hazard is caused (TRS 1970). The aim of measuring surface contamination and its extent, and afterwards to evaluate the activity per unit area in order to verify that the permissible limits are not being exceeded. The most common instruments used for surface contamination are scintillators, proportional counters, semi-conductor detectors and Geiger-Mueller detectors provided with thin entrance windows (TRS 1970, Oberhofer 1983). The choice of the instrument should depend on assessment of the parameters that could affect the surface contamination measurement. These are: the area to be monitored, the radionuclides present, the contamination level and the background radiation. Each instrument should be calibrated and its performance checked in a standard laboratory before its first use, after each repair, and then be recalibrated periodically, usually every 12 months (TRS 1970, CNEN 1988). The calibration process of such instruments involves the use of different radioactive standard sources (ISO 1988a, b). In this work, the responses of a scintillator, a proportional counter and two Geiger-Mueller detectors were studied in standard alpha and beta radiation beams, and their efficiency was determined