Decision making and the performance of emergency response survey meter

When we handle the radiation accident, we always stress on the importance of decision making and crisis management. Nevertheless, the basis for both of them is the quickly and correctly surveillance results read from survey meters. In 1999, an intercomparison of those currently used survey meters are made at the INER. The purpose of the comparison is to find the meters that can be used to detect the abnormal situation as soon as possible and to find the meters which can be used under high dose rate accurately. After discussing with CAEC officers, we decided that the ideal requirements for survey meters to respond abnormal situation are (1) the response time must be less than 2 seconds, (2) the minimum detectable dose rate should be as low as 0.1 to 0.2μSv/h and (3) either the precision or the energy response should stay less than ±20%, (4) the stability of each survey meter should be less than ±6%. The function of portable gamma spectrometer is preferred and the accuracy for measurement of dose rate higher than 10mSv/h should be less than ±20%. There are 18 brands of survey meters measured to determine the minimum detectable dose rate and response time. The minimum detectable dose rates are measured from both inside and outside of a 15cm thickness contamination free iron shielding and the response time for each survey meter is measured with a 1.85E11Bq Cs-137 source and a stop watch in a secondary calibration laboratory. The results are tabulated and plotted. On that plot, the axis represent the minimum detectable dose rate and the response time separately. So, we can compare the abnormal response ability with those survey meters and we find that 50% GM detectors and 33% scintillation detectors meet our requirement. To our surprise, the performance of scintillation detectors isn't as good as we expected. On the other hand, we measured the precision of 9 frequently used survey meters ranging from 0.05 to 50Sv/h. The response values are tabulated and plotted, too. This result can be used to select the most suitable survey meter to be used under emergency response. In this study, semiconductor type detector appears to perform excellently for he dose rate ranging from 0.5 to 500Sv/h. (author)