Calibration of radioactive contamination monitors for practical use in hospitals

Quantitative assessment of radioactive contamination is a desirable aim in any department using radionuclides. Guidance is available for calibration of contamination monitors with sealed reference sources but the calibrations obtained in this way are of limited practical use. In this work, we examined methods for calibration using radionuclides used in the hospital workplace. Calibration factors (s-1 per Bq.cm-2) were obtained for 99mTc, 131I, 90Y and 89Sr for three types of monitor for a range of contamination areas, and minimum detectable activities were calculated. Of the three detectors evaluated, the Berthold LB122/LB6357F proved the most sensitive for all radionuclides tested. The effect of contamination area was found to be significant; calibration factors for a particular monitor varied by up to a factor of 4 with contamination area, which has important implications, for example in the estimation of skin doses. User departments need to be aware of this variation and how to correct for it.