Effect of dopants on TL characteristics of LiF:Mg,Cu,P detectors
Abstract LiF:Mg,Cu,P detectors produced at the Institute of Nuclear Physics in Krakow have shown very good dosimetric characteristics. Understanding of the effect of the concentration and type of dopants is important in the characterization of TL materials. The aim of work was to investigate the influence of the type and concentration of the dopants on the photon energy response of these detectors by irradiations “in air” and on the ISO water phantom in the range of mean photon energies between 33 and 164 keV. The influence of dopants on the glow curves, sensitivity and reproducibility was also examined. Results showed that measured energy dependence values are lower compared to the theoretical values both “in air” and on phantom. The type and concentration of the dopants influence the shape of the glow curves and sensitivity while for energy dependence is more important the presence of certain activators, namely copper.
Dependence of LiF:Mg,Cu,P (MCP-N) Glow-Curve Structure on Dopant Composition and Thermal Treatment
In a systematic investigation of the effect of dopant composition on dosimetric characteristics of thermoluminescent LiF:Mg,Cu,P phosphor, 130 samples were prepared with different concentrations of all activators over the following ranges: Mg (0-1.0 mol%), Cu (0-0.5 mol%) and P (0-5.0 mol%). From each material a group of sintered detectors was produced. Parameters describing the shape of the glow curve were analysed after standard annealing at 240°C and after annealing at temperatures up to 400°C. It appears that the amplitude of the main dosimetric peak 4 depends on the concentration of Cu and Mg, showing a distinct maximum for certain concentrations of these dopants. Intensities of high temperature peaks tend to rise with increasing Mg and decreasing Cu concentration. The dependence of the amplitude of peak 4 on P concentration is a step function, rising by an order of magnitude as the amount of P exceeds a threshold value of 0.15 mol%. It appears that copper does not participate in the formation of traps nor of luminescent centres and plays an indirect role, that of inhibiting the growth of high-temperature peaks. Increase of annealing temperatures up to 270°C results in a decrease of the signal from high temperature peaks and in an increase of the main peak intensity (for most combinations of dopant composition). At annealing temperatures above 270°C intensities of all peaks decrease. This thermal susceptibility of LiF:Mg,Cu,P appears to be associated with the instability of Mg-related defects.
A Systematic Evaluation of The Dependence of Glow Curve Structure on the Concentration of Dopants in LiF:Mg,Cu,P
A systematic investigation of the properties of LiF:Mg,Cu,P has been performed with respect to the concentration of Mg (0-1.0mol%), Cu (0-0.5 mol%) and P (0-5.mol%) activators. 120 different samples of LiF:Mg,Cu,P material were prepared using uniform batches of chemical substrates. From each material a group of sintered chips was produced. Parameters describing glow curve shape were analysed after annealing at 240°C and photon irradiation. The results reveal that Cu has a very strong influence on glow curve structure, but a much weaker effect on the total TL intensity. The amplitude of peak 4 depends on both Cu and Mg, showing a distinct maximum for a certain content of these dopants. High temperature peaks tend to rise with increasing Mg and decreasing Cu concentration. The dependence of the amplitude of peak 4 on P concentration is a step function, rising by an order of magnitude as the amount of P exceeds a threshold value of 0.15 mol%. It seems that Mg is related mainly to trapping centres, while P mainly to luminescent centres. Cu does not appear to be directly involved in the trapping process.