Refurbishment and modernization of a thermo-luminescence dosimeter system using LabView virtual instrument software and validation of its results

A Thermo-Luminescence Dosimeter (TLD) system (Harshaw Model: 2271 and 2000B) which was used by the Atomic Energy Authority of Sri Lanka was recently refurbished and modernized by interfacing a Data Acquisition Module (UNIO-52) which is controlled through a virtual instrument software interface providing solutions to many existing deficiencies. The photomultiplier tube current and the current signal of the temperature sensor of the heater element of the TL chip were digitized by ADC0 and ADC1 of the UNIO 52 respectively. The LabView Software tool was used for the visualization of the glow curve (GC) from the output of ADC0 and the time-temperature profile (TTP) from the output of ADC1 on the same display. Radiation dose was calculated from integrated area of the GC within the recommended temperature range for the TL material used. The GC was visualized on the display from the average value of the previous ten consecutive readings of the output of the ADC0. Each reading was taken at every 0.25s. The GC area was calculated by taking the summation of data points displayed within the specified range of temperature. Validation of the software was carried out by applying an external triangular waveform from a Function Generator (TTi model: TG 4001) and DC voltage from a Power Supply (TTi model: PL3200MD), one at a time, directly to the analogue inputs of the UNIO-52. The amplitude of triangular wave with period of 10s, and DC voltage inputs were varied in steps and the integral calculation was carried out by software. The theoretical value of the GC area was calculated by summing up the values of 40 data points (10s X 4 points/s = 40) during the period of 10s. Accuracy of the time scale was measured by varying the period of the triangular wave form. Linearity of response and reproducibility of results were also examined by replacing the PMT signal with the triangular wave form and DC voltage signal through a precision resistor. Results showed a good accuracy and reproducibility. The accuracy of TLD dose results was verified by using a standard dosimetry calibration facility. Comparison of the results with a commercially available modern computerized TLD System (Harshaw model: 4500) also verified the validity of the results. (author)