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

Thermoluminescent dosemeters (TLDs) have been used to estimate the personal dose equivalent for external occupationally exposed workers in Tanzania. The reliability and precision of dose measurements and the accuracy of dose evaluation are important factors for the improvement and achievement of individual monitoring objectives. In this piece of work we describe a study of the major characteristics of TLDs (linearity of response, photon energy response, batch homogeneity and uniformity, calibration of TLDs and TLD systems in terms of operational quantities, fading, etc) in order to initiate a routine performance testing and quality assurance programme to be undertaken by central personal dosimetry services. The energy response of the dosemeters relative to that measured using Cs-137 gamma rays was found to vary between 1.0 and 1.3 over the range of 33-1250 keV (Co-60). The linearity of the response for the TL dose dependence in the dose range of 0.1-30 mGy for 48 keV and Cs-137 (662 keV) radiation protection qualities varied from 15% to 7% respectively, for both energies. The minimum detectable dose, the batch homogeneity and uniformity, and the batch reproducibility were found to be 0.1 mGy, 16%, and 9% respectively while the fading characteristic 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 the degree of accuracy achieved and the need for its improvement where necessary.