Phototransferred thermoluminescence characteristics of microcline (KAlSi3O8) under 470 nm blue- and 870 nm infrared-light illumination.

We report phototransferred thermoluminescence (PTTL) induced in microcline by 470 nm blue- and 870 nm infrared-light. A conventional thermoluminescence (TL) glow curve measured from a sample irradiated to 40 Gy produces five composite TL glow peaks P1, P2, P3, P4 and P5 at 90, 123, 166, 298 and 391 °C respectively. The sample produces PTTL peaks also identified as P1, P2, P3 and P4 following illumination by blue or infrared light after irradiation to 40 Gy and preheating to 400 °C. Step-annealing suggests the presence of deep electron traps associated with a signal beyond 500 °C. However, preheating to 500 °C and exposure to blue or infrared light does not produce significant PTTL peaks. For doses between 40 Gy and 100 Gy, the maximum PTTL is emitted within 60 and 150 s of blue light illumination. On the other hand, the same feature under the infrared light illumination occurs within 100-200 s of illumination. PTTL peaks P1, P2, P3 and P4 reproduced under blue light illumination have a linear dose response between 10 Gy and 100 Gy and those reproduced under infrared light illumination have a superlinear dose response between 10 and 100 Gy. In contrast, donor peak P5 in both cases follows sublinear dose response within the same dose range. Fading of PTTL peaks P1, P2, P3 and P4 as well as the donor peak P5 are negligibly small under blue light illumination compared to that of infrared light illumination. PTTL glow curves are also found to be properly reproducible.

Optically stimulated luminescence of cowrie shells.

Characteristics of continuous wave optically stimulated luminescence (CW-OSL) and linear modulation OSL (LM-OSL) from three different types of cowrie shells are presented. Irradiated samples were optically stimulated at 72 mW/cm2 for CW-OSL and linearly ramped from zero to 72 mW/cm2 to obtain LM-OSL. The measured CW-OSL and LM-OSL curves of the shells are each determined to consist of three components namely fast, medium and slow components. The fast, medium and slow LM-OSL components peak at 17.0 ± 0.8, 45.0 ± 1.8 and 140.8 ± 6.7 s respectively for all samples. In addition, peak positions are independent of dose. The photoionization cross-sections of the OSL traps for the three components estimated from CW-OSL are similar to those determined using LM-OSL. The OSL of the three components increases linearly with dose. The coefficient of variation of responses from repeated measurements of same aliquot lies below 2.3%. The shells are thus potential materials for retrospective dosimetry.

Thermoluminescence and infrared light stimulated luminescence of limestone (CaCO3) and its dosimetric features.

Thermoluminescence (TL) and infrared light stimulated luminescence (IRSL) of limestone (CaCO3) collected from the Mawsmai Cave, India is reported. Structural and compositional analyses show that the sample has a rhombohedral crystal structure and contains 33.45% of CaO. TL measured at 1 °C/s from a sample irradiated to 600 Gy produces three composite glow peaks P1, P2 and P3 at 92, 165 and 239 °C respectively. The nature of the glow peaks is suggestive of the presence of a continuum trap distribution with activation energy between 0.40 eV and 1.12 eV. As regards to dose response, the TL intensity of P1 increases at a uniform rate with dose between 10 and 1000 Gy. Interestingly, the intensity of P3 increases with dose through two uniform regions, one within 10-100 Gy and the other between 100 and 1000 Gy. The IRSL measurement produces ill-shaped decay curves. The IRSL intensity also increases with dose at two different uniform rates within 10-100 Gy and 100-1000 Gy. Residual TL recorded after each IRSL measurement shows similar dose response as that under the conventional TL. Regarding fading, P1 fades by 88% and P3 by 14% within 12 h of irradiation.

The effect of pre-dose on thermally and optically stimulated luminescence from α-Al2O3:C,Mg and α-Al2O3:C.

We report the effect of pre-dose on the thermoluminescence (TL) and optically stimulated luminescence (OSL) dose response of α-Al2O3:C,Mg and α-Al2O3:C. Before any luminescence measurement, the samples were irradiated with different doses, namely 100, 500 and 1000 Gy to populate the deep electron traps. This is the pre-dose. The results from TL and OSL studies are compared with results from samples used without any pre-measurement dose. The TL glow curves and OSL decay curves of α-Al2O3:C,Mg recorded after pre-doses of 100, 500 and 1000 Gy are identical to those from a sample used without any pre-dose. Further, the TL and OSL dose response of all α-Al2O3:C,Mg samples are similar regardless of pre-dose. In comparison, the TL glow curves and OSL decay curves of α-Al2O3:C are influenced by pre-dose. We conclude that the differences in the TL and OSL dose response of various pre-dosed samples of α-Al2O3:C are due to the concentration of charge in the deep traps. On the other hand, owing to the lower concentration of such deep traps in α-Al2O3:C,Mg, the TL or OSL dose responses are not affected by pre-dose in this material.

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

A comparative study of the dosimetric features of α-Al2O3:C,Mg and α-Al2O3:C relevant to thermoluminescence dosimetry is reported. A glow curve of α-Al2O3:C,Mg measured at 1°C/s after beta irradiation to 1 Gy shows two subsidiary peaks at 42°C (labelled as I) and 72°C (II) and the main peak at 161°C (III) whereas a glow curve of α-Al2O3:C measured under the same conditions shows the main peak at 178°C (II') and a lower intensity peak at 48°C (I'). Apart from these ones, there are several other peaks at temperatures beyond that of the main peak in both α-Al2O3:C,Mg and α-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 α-Al2O3:C,Mg and peaks I' and II' of α-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 α-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 α-Al2O3:C,Mg was found to decrease with increase in dose. However, no such behaviour was observed in α-Al2O3:C. The fading in both samples is discussed on the basis of a charge hopping mechanism.

Orthopaedic grade ultra-high molecular weight polyethylene: some features of the main thermoluminescence glow curve.

Thermoluminescence (TL) characteristics of orthopaedic-grade ultra-high molecular weight polyethylene have been investigated between 20 and 200 degrees C. The TL at 1 degrees C s(-1) consists of two glow curves, a weaker intensity peak at 115 degrees C and the main peak at 70 degrees C, studied in this work. TL intensity increases with beta irradiation but with a dose-response influenced by heating rate. On the other hand, the peak maximum is affected by both irradiation and repeated use of a sample. The glow curve shifts to higher temperatures with increase in heating rate but only slightly so with change in beta irradiation dose, properties suggestive of first-order kinetics. Kinetic analysis for activation energy and order of kinetics, based on the discrete trap model, produce somewhat conflicting results. Whereas qualitative analysis of peak symmetry show that first-order kinetics apply, geometrical analysis of the peak shape suggests that the order of kinetics might be other than first-order. Values of activation energy evaluated using the initial rise method were found to be dose dependent and for a given beta dose are in agreement with calculations from peak shape and initial rise methods but less so with results from variable heating rate method.

Towards models for analysis of time-resolved luminescence spectra from quartz.

Simple and stretched-exponential models for use in the analysis of time-resolved luminescence spectra from quartz are compared. The methods have been applied to evaluate lifetimes from portions of time-resolved luminescence spectra measured either during or after the luminescence stimulating pulse. We discuss the basis for use of the exponential functions as well as examine the application of, in this context, atypical stretched-exponential functions for analysis of time-resolved luminescence spectra from quartz.

A preliminary thermoluminescence and positron annihilation study of alpha-Al2O3:C.

The effects of pre-irradiation annealing on the thermoluminescence glow curves of gamma irradiated alpha-Al2O3:C have been studied for measurements between 30 and 500 degrees C. In particular, the response of the main dosimetric peak has been studied for gamma irradiation doses between 0.1 and 440 Gy and that of a subsidiary higher temperature glow peak for doses between 0.1 and 200 Gy. The response is observed to be linear only at low doses in agreement with previously reported data. The type and density of defects that may contribute to the observed dose response at various stages of the growth curve are discussed.

Time-resolved luminescence from annealed quartz.

The influence of annealing on the lifetime and luminescence intensity has been studied in quartz annealed at 873, 1073, 1173, and 1273 K and in unannealed quartz. Luminescence was stimulated by pulsed green (525 nm) light. Luminescence intensity increased as a function of temperature from 293 K to a peak at 373 K, and decreased thereafter to 473 K, the maximum temperature in the investigations. Luminescence lifetimes from both unannealed quartz and samples annealed at 873 K for up to 5 min were constant at about 40 micros below 373 K. Lifetimes decreased strictly monotonically with temperature in samples annealed above 873 K. Values of the activation energy for thermal assistance accounting for the increase in luminescence intensity, and of thermal quenching describing the decrease of luminescence intensity and luminescence lifetimes are presented.