Performance characteristics of LiF thermoluminescent dosemeters employed in the NationalPersonnel Radiation Dose Services in Tanzania

Abstract

Thermoluminescent dosemeters (TLDs) have been used to estimate the personal doseequivalent for external occupationally exposed workers in Tanzania. The reliability andprecision of dose measurements and the accuracy of dose evaluation are important factorsfor the improvement and achievement of individual monitoring objectives. In this piece ofwork we describe a study of the major characteristics of TLDs (linearity of response,photon energy response, batch homogeneity and uniformity, calibration of TLDs and TLDsystems in terms of operational quantities, fading, etc) in order to initiate a routineperformance testing and quality assurance programme to be undertaken by central personaldosimetry services. The energy response of the dosemeters relative to that measured using137Cs gamma rays was found to vary between 1.0 and 1.3 over the range of 33–1250 keV(60Co).The linearity of the response for the TL dose dependence in the dose range of 0.1–30 mGy for 48 keVand 137Cs (662 keV) radiation protection qualities varied from 15% to 7% respectively, for bothenergies. The minimum detectable dose, the batch homogeneity and uniformity, and thebatch reproducibility were found to be 0.1 mGy, 16%, and 9% respectively while the fadingcharacteristic of doped LiF after a received dose of 3 mGy was found to be 6.3%over a one-month period. These results are discussed in order to demonstrate thedegree of accuracy achieved and the need for its improvement where necessary.