High Temperature Thermoluminescence Research Articles

Dosimetric properties of the 570 K thermoluminescence peak of YAlO3:Mn crystals

We report results of the experimental study of thermoluminescent properties of the high-temperature TL peak at 570 K observed in YAlO3:Mn,Si crystals at low concentrations of manganese ions. The potential of this TL peak for thermoluminescent dosimetry of ionizing radiation is discussed. Main dosimetric properties of the TL peak including dose dependence, thermal fading and the effect of visible light exposure were studied.

Mysteries of LiF TLD response following high ionisation density irradiation: nanodosimetry and track structure theory, dose response and glow curve shapes

Three outstanding effects of ionisation density on the thermoluminescence (TL) mechanisms giving rise to the glow peaks of LiF:Mg,Ti (TLD-100) are currently under investigation: (1) the dependence of the heavy charged particle (HCP) relative efficiency with increasing ionisation density and the effectiveness of its modelling by track structure theory (TST), (2) the behaviour of the TL efficiency, f(D), as a function of photon energy and dose. These studies are intended to promote the development of a firm theoretical basis for the evaluation of relative TL efficiencies to assist in their application in mixed radiation fields. And (3) the shape of composite peak 5 in the glow curve for various HCP types and energies and following high-dose electron irradiation, i.e. the ratio of the intensity of peak 5a to peak 5. Peak 5a is a low-temperature satellite of peak 5 arising from electron-hole capture in a spatially correlated trapping centre/luminescent centre (TC/LC) complex that has been suggested to possess a potential as a solid-state nanodosemeter due to the preferential electron/hole population of the TC/LC at high ionisation density. It is concluded that (1) the predictions of TST are very strongly dependent on the choice of photon energy used in the determination of f(D); (2) modified TST employing calculated values of f(D) at 2 keV is in agreement with 5-MeV alpha particle experimental results for composite peak 5 but underestimates the 1.5-MeV proton relative efficiencies. Both the proton and alpha particle relative TL efficiencies of the high-temperature TL (HTTL) peaks 7 and 8 are underestimated by an order of magnitude suggesting that the HTTL efficiencies are affected by other factors in addition to radial electron dose; (3) the dose-response supralinearity of peaks 7 and 8 change rapidly with photon energy: this behaviour is explained in the framework of the unified interaction model as due to a very strong dependence on photon energy of the relative intensity of localised recombination and (4) the increased width and decrease in T(max) of composite peak 5 as a function of ionisation density is due to the greater relative intensity of peak 5a (a low-temperature component of peak 5 arising from two-energy transfer events, which leads to localised recombination).

Synthesis, Characterization, Luminescence and Defect Centres in CaYAl3O7:Eu3+ Red Phosphor

CaYAl(3)O(7):Eu(3+) phosphor was prepared at furnace temperatures as low as 550°C by a solution combustion method. The formation of crystalline CaYAl(3)O(7):Eu(3+) was confirmed by powder X-Ray diffraction pattern. The prepared phosphor was characterized by SEM, FT-IR and photoluminescence techniques. Photoluminescence measurements indicated that emission spectrum is dominated by the red peak located at 618 nm due to the (5)D(0)-(7)F(2) electric dipole transition of Eu(3+) ions. Electron Spin Resonance (ESR) studies were carried out to identify the centres responsible for the thermoluminescence (TL) peaks. Room temperature ESR spectrum of irradiated phosphor appears to be a superposition of two distinct centres. One of the centres (centre I) with principal g-value 2.0126 is identified as an O(-) ion while centre II with an isotropic g-factor 2.0060 is assigned to an F(+) centre (singly ionized oxygen vacancy). An additional defect centre is observed during thermal annealing experiments and this centre (assigned to F(+) centre) seems to originate from an F centre (oxygen vacancy with two electrons). The F(+) centre appears to correlate with the observed high temperature TL peak in CaYAl(3)O(7):Eu(3+) phosphor.

TL, OSL and ESR studies on beryllium oxide

Abstract Electron spin resonance (ESR) studies were carried out to identify the defect centres responsible for the thermoluminescence (TL) and optically stimulated luminescence (OSL) processes in BeO phosphor. Two defect centres were identified in irradiated BeO phosphor by ESR measurements, which were carried out at room temperature and these were assigned to an O− ion and Al2+ centre. The O− ion (hole centre) correlates with the main 190 °C TL peak. The Al2+ centre (electron centre), which acts as a recombination centre, also correlates to the 190 °C TL peak. A third centre, observed during thermal annealing studies, is assigned to an O− ion and is related to the high temperature TL at 317 °C. This centre also appears to be responsible for the observed OSL process in BeO phosphor.

Energy levels in YPO4:Ce3+,Sm3+ studied by thermally and optically stimulated luminescence

Energy-resolved optically stimulated luminescence (OSL) spectra and thermoluminescence (TL) glow curves of a powder sample of YPO4:Ce3+,Sm3+ were measured to investigate the nature of the trapping centre and to locate its energy level relative to the valence and conduction bands of the YPO4 host. The high-temperature glow peak could unequivocally be assigned to Sm2+ (thus Sm3+ acts as an electron trap). The trap depth of this centre, as derived from the OSL excitation spectra, is in good agreement with the Dorenbos model prediction. The OSL excitation spectra also reveal excited states of Sm2+ well below the conduction band. These excited states produce a broadening of the high-temperature TL glow peak and also cause the activation energy determined by the Hoogenstraten method to underestimate the trap depth.

Characteristics of the high temperature thermoluminescence in LiF:Mg,Ti (TLD-100): The effects of batch history

Abstract The high temperature thermoluminescence (HTTL) in the glow curve of LiF:Mg,Ti (TLD-100) is of continuing interest due to the dependence of the HTTL on ionization density. Following high ionization density irradiation, the intensity of the HTTL relative to peak 5 is much greater than the same ratio following low ionization density irradiation. Special attention has focused on the details of the linearity/supralinearity of the HTTL dose response at levels of dose between 10 and 500 mGy and whether the batch history (previous irradiation and annealing) affects the HTTL dose response? In this paper we demonstrate that batch identity leads to differences of ∼100% in the degree of the supralinearity of the dose response of peak 7 between two groups of TLD-100 chips. The results suggest that there may be significant non-universalities in the HTTL dose response and that further research is required to provide a sound basis for the use of the HTTL of TLD-100 in dosimetric applications.

Experimental investigation of the 100 keV X-ray dose response of the high-temperature thermoluminescence in LiF:Mg,Ti (TLD-100): theoretical interpretation using the unified interaction model

The dose response of LiF:Mg,Ti (TLD-100) chips was measured from 1 to 50,000 Gy using 100 keV X rays at the European Synchroton Radiation Facility. Glow curves were deconvoluted into component glow peaks using a computerised glow curve deconvolution (CGCD) code based on first-order kinetics. The normalised dose response, f(D), of glow peaks 4 and 5 and 5b (the major components of composite peak 5), as well as peaks 7 and 8 (two of the major components of the high-temperature thermoluminescence (HTTL) at high levels of dose) was separately determined and theoretically interpreted using the unified interaction model (UNIM). The UNIM is a nine-parameter model encompassing both the irradiation/absorption stage and the thermally induced relaxation/recombination stage with an admixture of both localised and delocalised recombination mechanisms. The effects of radiation damage are included in the present modelling via the exponential removal of luminescent centres (LCs) at high dose levels. The main features of the experimentally measured dose response are: (i) increase in f(D)(max) with glow peak temperature, (ii) increase in D(max) (the dose level at which f(D)(max) occurs) with increasing glow peak temperature, and (iii) decreased effects of radiation damage with increasing glow peak temperature. The UNIM interpretation of this behaviour requires both strongly decreasing values of ks (the relative contribution of localised recombination) as a function of glow peak temperature and, as well, significantly different values of the dose-filling constants of the trapping centre (TC) and LC for peaks 7 and 8 than those used for peaks 4 and 5. This suggests that different TC/LC configurations are responsible for HTTL. The relative intensity of peak 5a (a low-temperature satellite of peak 5 arising from localised recombination) was found to significantly increase at higher dose levels due to preferential electron and hole population of the trapping/recombination complex giving rise to composite glow peak 5. It is also demonstrated that possible changes in the trapping cross section of the LC and the competitive centres due to increasing sample/glow peak temperature do not significantly influence these observations/conclusions.

Direct evidence for the participation of band-tails and excited-state tunnelling in theluminescence of irradiated feldspars

The significance and extent of band-tail states in the luminescence and dosimetryproperties of natural aluminosilicates (feldspars) is investigated by means of studiesusing low temperature (10 K) irradiation and optically stimulated luminescence(OSL) stimulation spectroscopy, and thermoluminescence (TL) in the range10–200 K, made in comparison with high temperature (300 K) irradiation andphoto-transferred OSL and TL investigations undertaken at low temperature. Thesemeasurements allow mappings of the band-tails to be made; they are found to be∼0.4 eV in extent in the typical materials studied. Furthermore, by populating charge trappingcentres at high temperature (300 K) and monitoring the OSL stimulation spectra attemperatures in the range 10–300 K, clear evidence is presented for the presence of boththermally activated and non-thermally activated OSL processes; it is argued that theformer result from thermally activated hopping through the band-tail states, whilst thelatter are due to tunnelling processes, either from the excited state of the OSL centres orthrough the tail states. The spectral measurements are supported by analysis of thetemporal dependence of the OSL signals, which correspond to either tunnelling or generalorder kinetic decay processes.

Investigation of the Sediment Movement along the Tenryu–Enshunada Fluvial System Based on Feldspar Thermoluminescence Properties

The thermoluminescence (TL) properties of feldspar were used to investigate the sediment movement processes in a fluvial–coastal system. Field samples were collected at various locations along the Tenryu River and the Enshunada Coast in Japan. After a series of pretests, an appropriate TL measuring sequence was proposed for this study. Applying this approach, the natural TL intensity of feldspar grains was measured. Owing to the young age of the research area, it was assumed that the natural TL difference was ascribed to the sample depositional environment under which different possibilities of sunlight exposure exist. Surface sediment particles in the target area were classified into three groups in terms of TL intensities, i.e., river sand with large TL signals, coastal sand with medium TL signals, and dune sand with small TL signals. Stratified configuration of the Nakatajima Coastal Dune was observed from the underground-sample TL glow curves with a top, windblown, dune-sand layer; a bottom, wave-induced, coastal sand layer; and a mixing layer in between. A rather complex sediment-movement pattern in front of the Tenryu River mouth was revealed after investigation of the underwater samples. Because of the seawater influence, acting as an ultraviolet filter to sunlight, underwater samples present a larger, high-temperature TL peak than the low-temperature peak; whereas these two are almost the same for ground samples.

Update on AAPM Task Group No. 43 Report--Brachytherapy and TLD

Sir, The non-universality of many of the thermoluminescent (TL) characteristics of commonly used dosimetric materials, in general, and LiF:Mg,Ti, in particular, has been the subject of much discussion and controversy(1,2). Indeed, it appears to be one of the main disadvantages of thermoluminescent dosimetry (TLD). The following are the primary reasons for the lack of universality in the TL properties of peak 5 (the major glow peak used for dosimetric applications) in LiF:Mg,Ti. (1) In the preparation of the material, the TL trapping and luminescent centres are formed from the addition of impurities at the parts per million (ppm) level to the crystal-growth-melt (∼150 ppm w−1 Mg and ∼10 ppm w−1 Ti). Thus, other unwanted or stray impurities at the ppm level can and do create variations in the TL characteristics. (2) The lack of a universally and generally accepted experimental protocol controlling the various aspects of thermal and storage history, annealing, readout and analysis. These non-universalities can lead to very significant problems of interpretation which can be seriously exacerbated, especially when high precision and accuracy are required in the dosimetric application. An illustrative example is in the application of TLDs to low-energy X-ray interstitial brachytherapy using 125I (∼27.3 keV) and 103Pd (∼20.1 keV) X rays. One of the largest errors involved in this application as listed in the American Association of Physicists in Medicine (AAPM) Task Group No. 43 Report(3) is claimed to have a value of 5% (out of a total combined uncertainty of 8.7%) due to uncertainties in the experimental evaluation of the X-ray over-response. The over-response refers to an increased relative sensitivity to X rays <300 keV in energy and is ∼10% greater than that expected from the energy dependence of the mass–energy absorption coefficients. The phenomenon was probably first measured by Cameron et al.(4) 45 years ago, and the results of 10 independent experimental investigations for peaks 4 + 5 in LiF:Mg,Ti (TLD-100) were reviewed in detail 35 years ago(5). Between 20 and 30 keV, the over-response ‘for that part of the glow curve measured up to a maximum temperature of 240°C in the work of Budd et al.(5)’ appears to be 10–15%, but some early investigations actually reported an under-response at these low energies. A more modern compilation for LiF:MTS-N (LiF:Mg,Ti manufactured in Poland)(6) shows the same general features, i.e. an over-response of ∼10% at energies above 30 keV. But again, at 20 keV, the experimental data indicates an under-response of ∼10%. Two of the data points are 10% lower than what would be expected using the mass–energy absorption coefficients, one data point exactly agrees. These differences certainly arise in part (or in full) from the lack of a universally accepted protocol and have been the subject of fairly recent papers in the medical-physics dosimetry community attempting to understand the reasons behind the discrepancies in the various experimental measurements and Monte Carlo simulations(7). It deserves mention that the over-response is glow-peak-dependent; for the high-temperature thermoluminescence (HTTL: referring to thermoluminescence appearing at temperatures above ∼ 240°C), the over-response is ∼100%. Since the intensity of the HTTL relative to peak 5 is ∼10–20% at a dose level of 1 Gy, inclusion of even part of the HTTL in the TL signal may therefore influence the measured over-response of peaks 4 + 5 at the few per cent level. The relative intensity of the HTTL in the glow curve is critically dependent on the cooling rate following the 400°C pre-irradiation anneal as well as other material and batch-dependent factors(8,9). This might be an area of endeavour in which the application of computerised glow-curve deconvolution would decrease the discrepancies measured in various experimental investigations(10).

Further studies on higher temperature TL glow peaks of 7LiF:Mg,Ti

Thermoluminescence (TL) characteristics of the higher temperature peaks of LiF:Mg,Ti, which exhibit a unique property of high relative response to high LET radiation, were studied in view of some recent findings and discussions. By making separate readouts of dosimetric peaks (mainly peak 5) and higher temperature peaks (mainly peak 7), the precision in TL measurements, reusability and, fading were found comparable for the TL readouts in the two regions. However, the intensity of higher temperature peaks was found to be susceptible to the annealing treatments. In the standard annealing treatment of LiF:Mg,Ti, namely, 400 °C for 1 h followed by 100 °C for 2 h, the intensity of the higher temperature glow peaks was significantly affected when the second step of lower temperature annealing treatment at 100 °C for 2 h was not used. The dose response function f( D) of higher temperature peaks to gamma rays in the range from 30 to 150 mGy was found to be within about 10% (−4 and +9%) but above 200 mGy it increased sharply. The intricacies of dosimetry of mixed fields of low and high LET radiation are discussed.

Thermoluminescence kinetic study of binary lead-silicate glasses

This paper describes a detailed experimental study of the thermoluminescence (TL) properties of four binary lead-silicate glasses, with PbO concentrations ranging from 32% to 62% in mole percent. The TL glow peaks between room temperature and 300 °C were analyzed using a systematic thermal cleaning technique. The T max– T stop and E– T stop methods of analysis were used to identify the number of peaks under the glow curves, and to obtain the activation energy E for each TL trap. A computerized glow curve fitting analysis is used to fit the experimental data to four first-order peaks with maxima at temperatures of 54, 80, 110 and 210 °C, as measured with a heating rate of 2 °C/s. The kinetic parameters of the glow-peak at 210 °C were confirmed by using phosphorescence decay methods of analysis. The TL traps associated with the low-temperature TL peak at 54 °C are found to depend strongly on the PbO concentration of the samples, while the higher-temperature TL peaks show a behavior independent of the PbO concentration. The activation energy E and frequency factor s of the low-temperature TL trap associated with the peak at 54 °C are consistent with a trap involving a delocalized transition through the conduction band. However, the activation energies and frequency factors for the higher-temperature TL traps are consistent with traps involving localized transitions via an excited state below the conduction band. The data suggest that these higher-temperature TL traps are associated with the common silicate matrix in these binary silicate glasses.

Investigation of the ionisation density dependence of the glow curve characteristics of LIF:MG,TI (TLD-100).

The dependence of the shape of the glow curve of LiF:Mg,Ti (TLD-100) on ionisation density was investigated using irradiation with (90)Sr/(90)Y beta rays, 60 and 250 kVp X rays, various heavy-charged particles and 0.2 and 14 MeV neutrons. Special attention is focused on the properties of high-temperature thermoluminescence; specifically, the behaviour of the high-temperature ratio (HTR) of Peaks 7 and 8 as a function of batch and annealing protocol. The correlation of Peaks 7 and 8 with average linear-energy-transfer (LET) is also investigated. The HTR of Peak 7 is found to be independent of LET for values of LET approximately >30 keV microm(-1). The behaviour of the HTR of Peak 8 with LET is observed to be erratic, which suggests that applications using the HTR should separate the contributions of Peaks 7 and 8 using computerised glow curve deconvolution. The behaviour of the HTR following neutron irradiation is complex and not fully understood. The shape of composite Peak 5 is observed to be broader following high ionisation alpha particle irradiation, suggesting that the combined use of the HTR and the shape of Peak 5 could lead to improved ionisation density discrimination for particles of high LET.

Crystal Growth and Scintillating Properties of Zr/Si-Codoped ${\rm YAlO}_{3}:{\rm Pr}^{3+}$

Zr,Pr-codoped and Si,Pr-codoped single crystals were grown from the melt by the micro-pulling-down method. The effect of Zr/Si-codoping on YAIO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> :Pr scintillation properties, such as radioluminescence, scintillation light yield and decay time, was investigated. Absorption spectra of as-grown and air-annealed samples reveal the presence of color centers. The possible nature of the charge traps detected by high temperature thermoluminescence is discussed.

Fading characteristics of martian analogue materials and the applicability of a correction procedure

The anomalous fading of trapped charge in martian analogue materials such as basalt and andesite rock samples is measured. Optically stimulated luminescence (OSL) signals show rapid fading (of between 4% and 27% per decade). Fading rates obtained using high temperature thermoluminescence signals are smaller. The importance of knowing whether a standard fading correction method is applicable to samples of unknown age is illustrated by application to an ‘infinitely old’ known-age basalt, for which both the uncorrected and fading-corrected natural signals lie within the approximately linear region of the growth curve.

Letters to the Editor

Sir, Comments to the author's response to our letter on ‘The thermoluminescence dose–response and other characteristics of the high-temperature TL in LiF:Mg,Ti (TLD-100)’ by Y. S. Horowitz, L. Oster and H. Datz. The response of Horowitz(1) to our comments(2) to the above-mentioned article(3) contains inaccuracies which must be addressed. We object to the response to our previous letter to the editor(2) in the following respects. Even the most ardent believer in his cause should take care not to ignore facts and thereby come to biased conclusions, especially in a scientific dispute. In the opening sentence of his response to our comments 1 and 2, Horowitz incorrectly ‘quotes’ our claim that ‘the high-temperature thermoluminescence (HTTL) dose response is consistent with linearity’(1). It is definitely not what we mentioned in point 2(2). We must stress again that our true claim is that, for the low dose range, the gamma non-linearity is not observable, being within the experimental uncertainties range, which is obviously a different view. This point is mentioned also by other authors, but Horowitz continues to disregard the works of others in the field of application of HTTL to dosimetry by taking again into account our examples to be the only relevant material and ignoring other articles published on the subject. Almost from the beginning of studying the thermoluminescence phenomenon and its application to dosimetry and up to the present days, this subject has been dealt with. A review on this issue(4) mentions 12 works on the applications of HTTL with 6LiF for thermal neutron fields alone, many other works refer to fast neutrons. Out of the 12 works mentioned, 8 were published in international journals. One work reports practical routine application, and an American patent on the subject was registered as well.

Some dosimetric characteristics of the high temperature TL in LiF:Mg,Ti (TLD-100)

Various characteristics of the high temperature TL (HTTL) in the glow curve of LiF:Mg,Ti (TLD-100) are reviewed. Special emphasis is placed on the question of the linearity/supralinearity of the HTTL dose response at low dose levels from 2.5 to 250 mGy. It appears that a mild HTTL supralinearity of approximately 15–50% for each dose decade may be present between 5 and 250 mGy followed by an abrupt and rapid increase in the supralinearity above 250 mGy. However, difficulty in the estimation of background and the great variability in the protocols of measurement does not allow a definitive conclusion.

Letters to the Editor

Sir, Comments on ‘The thermoluminescence dose-response and other characteristics of the high-temperature TL in LiF:Mg,Ti (TLD-100)’ by Y. S. Horowitz, L. Oster and H. Datz This recent article(1) was intended to be a review on the subject and it reflects the view of its authors, as already published in the past. When discussing the dose–response issue (by gas and contact heating) the works of two groups (us being one of them) are discussed at length and in much detail, somewhat outside the scope of a balanced review. The article contains claims that are problematic and need to be discussed in depth, yet we find it important to present here some short comments on several issues raised, in particular the ones related to the chapter ‘HTTL dose-response via hot gas non-linear chip heating’, which is entirely dedicated to criticism of the experimental method in our works(...

The thermoluminescence dose response and other characteristics of the high-temperature TL in LiF:Mg,Ti (TLD-100)

Various characteristics of the high-temperature thermoluminescence (HTTL) in the glow curve of LiF:Mg,Ti (TLD-100) are reviewed. The proposed applications of the HTTL to mixed-field radiation dosimetry are outlined with special emphasis on the question of the linearity/supralinearity of the HTTL dose-response at low dose levels from 2.5 to 250 mGy. Recent measurements of the HTTL dose-response using non-linear hot-gas heating and linear planchet heating are discussed in detail. It appears that a mild HTTL supralinearity of approximately 15-50% for each dose decade may be present, followed by an abrupt and rapid increase in the supralinearity >250 mGy. However, difficulty in the estimation of background and the great variability in the protocols of measurement do not allow a definitive conclusion. There is much work to be done in the areas of protocol standardisation, materials selection, methods of data analysis and especially the details of background behaviour, and subtraction before the HTTL can become a reliable dosimetric tool.

Letters to the Editor

Sir, Comments on ‘Observation of enhanced efficiency in the excitation of ion-induced LiF:Mg,Ti thermoluminescent peaks’ G. Massillon., I. Gamboa-deBuen and M.E. Brandan, J. Appl. Phys. 100, 103521–1 (2006). In the above paper by Massillon et al., the authors have described experimental measurements of the heavy-ion relative TL efficiency of the high-temperature peaks in LiF:Mg,Ti (TLD-100) and, as well, their interpretation of the data in the framework of Track Structure Theory (TST)(1) and Modified Track Structure Theory (MTST)(2). In order to allow the reader an appreciation of the errors and conceptual failings involved in the efforts of Massillon et al. to interpret/analyse their data, a brief review of TST and MTST is required as well as a short description of what is commonly referred to as ‘high-temperature thermoluminescence’ or HTTL in LiF:Mg,Ti (TLD-100). The basic premise in the calculation of heavy charged particle (HCP) radiation effects in both TST and MTST is that the radiation effects of HCPs are due to the average dose delivered by the secondary electrons created by the HCP slowing down; and can therefore be predicted by the experimentally measured gamma-ray/electron dose–response folded into the radial dose distribution of the HCP. Radial dose profiles explicitly neglect the stochastic processes of the secondary electrons liberated by the HCP which, of course, are considered to be important in the microdosimetric treatment of radiobiological systems. In TL, these stochastic processes can be neglected since the TL signal is obtained or is measurable from the HCP interaction only at high levels of fluence, i.e. >105 cm−2 where the effects of stochastic processes which might arise in single tracks are completely averaged out. Of course, in solid-state systems, the radial dose distribution cannot be directly measured experimentally as in gaseous systems. These, therefore, have been calculated analytically(3) or obtained by track segment Monte Carlo calculations(4). In general, for low-energy proton and helium ions in the energy range 1–10 MeV, the calculated dose values start at MGy levels near the track axis, with a dependence on radial distance decreasing approximately as r−2 and reaching ∼Gy dose levels at distances of several hundreds to a few thousand Å from the track axis. More recently, full track radial dose profiles have been calculated for low-energy proton and helium ions using the Monte Carlo code FLUKA in nanometer-sized volumes(5). At these low proton and helium energies, the ions are stopped in the TL sample so that the nanometric FLUKA full track calculations describe the HCP slowing down and stopping process in a manner far more resembling the experimental situation than track segment calculations, and this particular point will be touched on later in this comment.