A COMPARATIVE STUDY OF THE DOSIMETRIC FEATURES OF α-Al2O3:C,Mg AND α-Al2O3:C

A comparative study of the dosimetric features of alpha-Al2O3:C,Mg and alpha-Al2O3:C relevant to thermoluminescence dosimetry is reported. A glow curve of alpha-Al2O3:C,Mg measured at 1A degrees C/s after beta irradiation to 1 Gy shows two subsidiary peaks at 42A degrees C (labelled as I) and 72A degrees C (II) and the main peak at 161A degrees C (III) whereas a glow curve of alpha-Al2O3:C measured under the same conditions shows the main peak at 178A degrees C (II') and a lower intensity peak at 48A degrees C (I'). Apart from these ones, there are several other peaks at temperatures beyond that of the main peak in both alpha-Al2O3:C,Mg and alpha-Al2O3:C. However, the latter are not included in this study. We report a comparative quantitative analysis of dose response and fading of peaks I, II and III of alpha-Al2O3:C,Mg and peaks I' and II' of alpha-Al2O3:C. Analysis shows that the dose response of peaks I and III is sublinear within 1-10 Gy whereas that of peak II is superlinear within 1-4 Gy followed by a sublinear region within 4-10 Gy. In comparison, the dose response of peak I' is superlinear within 1-4 Gy followed by a sublinear region within 4-10 Gy whereas that of peak II' is sublinear within 1-4 Gy followed by a superlinear region within 4-10 Gy. As regards to fading corresponding to 1 Gy, peak I is very unstable and fades within 300 s, peak II is more stable and takes up to 43200 s to fade. In comparison, peak III fades down to 30% of its initial intensity within 2400 s. Interestingly, between 2400 and 800 s, the intensity fades by 17% only. Regarding fading in alpha-Al2O3:C, peak I' fades within 600 s whereas peak II' shows an inverse fading behaviour up to 64800 s. The rate of fading for peaks I, II and III in alpha-Al2O3:C,Mg was found to decrease with increase in dose. However, no such behaviour was observed in alpha-Al2O3:C. The fading in both samples is discussed on the basis of a charge hopping mechanism.