Evaluation of calibration factors of digital survey meters in a secondary standard dosimetry laboratory

Abstract

The calibration of radiological survey meters is an important consideration in achieving standardisation of doses. This provides traceability for field instruments to an International System of Units. Seventy-one digital survey meters were calibrated by the substitution method in a 137Cs beam in a secondary standard dosimetry laboratory using a PTW spherical ionisation chamber coupled to a Physikalisch-Technische-Werkstaetten (PTW) UNIDOS Electrometer. The calibration factors determined ranged from 0.59 to 1.98. Thirty-six pieces of equipment have their calibration factors within 0.9-1.1. A total of 36% of the survey meters recorded calibration factors corresponding to a percentage deviation above 20% whilst 64% fell within 20% deviations from the true value. The best value of a calibration factor obtained in this work was 1.00 from two survey meters. The errors due to survey meters being out of calibration can usually be corrected by frequent recalibration.