Quality Assurance and Quality Control Studies on TLD Based Dosimetry Services by the University Radiation Safety Committee of King Abdulaziz University
W.H. Abulfaraj; S.I. Bhuiyan; T.M. Ahmed; and E. Elmohr (King Abdulaziz University, Jeddah 21589, KSA)
TLD Services are rendered for personnel dosimetry, work place and environmental monitoring by the University Radiation Safety Committee (URSC), King Abdulaziz University. The objective of this study is to design QA program for TLD based dosimetry services to minimize deviation in dose evaluation. The QA & QC program addressed administrative data/information, equipment checking, issuing/processing of the dosimeters, dose evaluation, record keeping, reporting, traceability and reproducibility, reviews and external audits. Systematic errors in dose evaluation were identified and minimized. Intercomparison program is established with the National SSDL facility and National Regulatory Authority ( KACST) to demonstrate the index of the technical stage practiced. The general aspects addressed are: type of personal dosimeter, calibration procedures, photon spectral dependence, TL response linearity, reproducibility, uniformity, fading, energy response, light sensitivity, background corrections. Series of experiments were conducted to standardize the calibration procedure and the generation of DCF using 137Cs Calibrator with Farmer and UNIDOS Dose Masters. Factors influencing the sensitivity of calibrations are identified. Typical value of sd and Coefficient of Variation in DCF used in the latest intercomparison program (Nov. 04) are ± 0.006 and 3.48%, respectively. The same for the 1St intercomparison ( April, 02) was 0.0185 and 10.2% respectively. Relative error between the measured and calculated doses slid down from 7.13% to 0.66%. TLD reader's operating parameters were set with internal checks creating constant measurement conditions. The overall system performance was assessed using control dosimeters exposed to known doses of radiation. Internal Audit Process and Blind Tests are introduced that direct the logical steps for measurement, analysis and improvement of Quality Management System. First successful National Intercomparison program results for B Bias, sd, and the summation of both are 0.27 [ acceptance limit 0.30], 0.06 [acceptance limit 0.35], and 0.33 [ acceptance limit 0.50] respectively. KACST follows ANSI protocol. The same values can be compared with latest intercomparison results; 0.13, 0.06 and 0.19 respectively. The results presented show improvement in evaluation of doses, the achieved Standard, certified by KACST, and its applicability in field dosimetry.
