TL dosimetry using extracted and cleaned sand to measure gamma-ray dose rate at a liquid sewage sludge irradiation facility

In an earlier study, we investigated the thermoluminescence (TL) properties of the sand collected from sewage sludge, after various extensive cleaning procedures and irradiation of gamma rays under controlled conditions in the laboratory. In the present investigation, the sand separated from the irradiated sludge was used to estimate the radiation processing absorbed dose to sludge at the sludge hygienisation research irradiator (SHRI), Baroda. Although, the relative TL sensitivity of H2O2- and HF-treated sludge sand samples was 4.00% and 0.07%, respectively, of that of LiF TLD-100, a well known TL phosphor used in radiation dosimetry, they were quite useful for dosimetry of the liquid sludge irradiator, when using TL calibrations of sand from sludge collected from sludge irradiator inlet. A useful dose range for such calibration is 0.3-4 kGy. A dose-vs-TL response calibration curve was plotted for the 220 degrees C TL glow peak for H2O2- and HF-treated sludge sand samples collected at the sludge irradiator inlet from an unirradiated batch, in order to estimate dose absorbed in the corresponding batch of the irradiated sludge collected at the sludge irradiator outlet. Using this method, the absorbed dose rate delivered to the sludge during irradiation at SHRI was estimated to be 0.70 +/- 0.02 kGy per hour. The paper also reports results of a dosimetry intercomparison for H2O2- and HF-treated sand samples, and LiF TLD-100 TL phosphor. The estimated gamma ray doses were nearly the same for all the three systems irradiated for the same exposure times. (C) 1997 Elsevier Science Ltd.