Comparison of dose rate measurements of commercially available hand-held gamma detectors with radiation protection dose meter

The control of rooms and areas where nuclear or radioactive material is stored or used is often performed with the use of commercially available hand-held gamma detectors using their dose or dose rate measurement capability. These devices are also often used by policemen or firemen. Reliable dose rate values are of great importance for the personal safety of the user in case of an elevated radiation field or generally for a first estimation of the threat generated by the radiation source. Therefor dose rate measurements were performed at Fraunhofer INT with the available hand-held gamma detectors under identical conditions. Seven hand-held gamma detectors of different type and size were investigated. The results of the dose rate measurements were compared among each other. For an assessment of the quality of the dose-rate measurements with hand-held gamma detectors a comparison with a calibrated dose rate measuring device for radiation protection FH 40 was made. It was seen that each hand-held gamma detector gave reproducible results for the gamma dose rate. However, the measured mean of the dose rate measurements with each hand-held device differed considerably, at a maximum by a factor of 3. Normally the measurement values were in the same order of magnitude. Except one all devices were not calibrated for radioprotection purposes. Taking into account that in Germany even for devices intended for radioprotection purposes only a precision of the dose rate of +/- 30 % is required the measurement results with hand-held devices can be regarded as reasonable good. Dose rate measurements with hand-held gamma detectors should be handled with care but in general the values obtained are good enough for personal safety and a first threat estimation although in general first responders would be required to carry a special radiation protection dosimeter in addition.