Main TL Research Articles

Radioluminescence (RL) behaviour of Al 2O 3:C-potential for dosimetric applications

The radioluminescence (RL) of carbon doped aluminium oxide (Al 2O 3:C) TL dosimeter material (TLD-500) was investigated using a 137Cs conversion electron source (which also emits β and γ) for simultaneous irradiation and luminescence excitation. Furthermore, RL dosimetry characteristics of this material were studied. The main RL emission occurs at 420 nm. That matches the known main TL and OSL emissions for this material as well as an emission that was investigated in earlier RL studies, excited at higher energies (4 MeV electrons) and very high pulse delivered doses (≈800 kGy·s −1). Furthermore, the saturation dose for the main peak is reached at the dose level of ≈80 Gy as known from TL and earlier RL investigations. Other peaks at 700 and 790 nm and broad emission bands at photon energies higher than 3.00 eV and others between 2.00 and 2.50 eV were observed. The 700 nm emission shows growth also at higher dose levels, and saturates at an estimated dose of ≈800 Gy. The 790 nm emission reaches its maximum intensity at ≈10 Gy absorbed dose. The reported results give an outlook to the usability and the potential of Al 2O 3:C combined with RL measurements for radiation dosimetry as well as for beta source calibration, using radioluminescence.

Effects of predose treatment on the thermoluminescence in synthetic quartz

The effects of thermal annealing and of exposure to high β doses as well as of the pre-dose treatment on the TL sensitivity were studied separately for the main 370 and 460 nm emission bands. These bands were differently influenced by the treatments. The thermal activation energies of the main TL peaks were the same for the two emission bands, indicating that the carriers are thermally released from the same traps. The observed changes in the TL intensities are attributed to phase transitions of the crystal.

The wavelength dependence of light-induced fading of thermoluminescence from α-Al 2O 3:C

This paper reports on the wavelength dependence, over the range 340–650 nm, of the light-induced fading of the main dosimetric TL signal from α-Al 2O 3:C. The data were obtained for either fixed photon flux or fixed photon energy, using either samples which were annealed after each TL readout and before re-use or samples which were unannealed. Photoconductivity and PTTL data suggest that the fading is due to the optical stimulation of charge from the traps into the delocalized bands. At a given wavelength the decay is approximately first-order for the first 90% of the decay. The decay constant, for a given photon flux, is dependent upon wavelength in the same manner as the efficiency for TL fading. At short wavelengths it is necessary to accout for the phototransfer of charge from deep traps into the dosimetry traps and thus the exact wavelength dependence is governed by the radiation and thermal history of the sample. The dose dependence of the TL peak suggests that it is caused by an overlap of several peaks resulting from an array of closely spaced energy levels.

Glow Curve Control of the Maximum Readout Temperature: Application to LiF GR-200

The influence of the maximum readout temperature on the LiF GR-200 dose response was studied. A fast heating rate (8°C.s -1 ) and a new method to set the maximum readout temperature were employed for this study. The new method determines on each measurement the maximum temperature with reference to the position of the main TL peak. This is achieved through the on-line analysis of the glow curve during heating. The good measurement reproducibility attained by using this method and a previously described computerised method for TL evaluation is also presented.

A study of the main glow peak for CaF 2:Mn

The overlapped glow peaks of CaF 2:Mn (with the composition of the main glow peak around 260°C) become distinguishable through a series of high-level irradiations. Our investigation revealed the fact that the main glow peak consists of three closely approximate peaks,denoted as P 2, P 3 and P 4. These three peaks together with P 1, which appears only under high exposures, constitute the main TL spectrum from room temperature to 350°C. The P 2 is believed to be related to the electron trap defect, F A center, and contributes to approx. 90% of the cooled optically stimulated luminescence (COSL) response. The other peaks are made by hole trap defects, modified V K centers and/or the oxidation of Mn 2+ to Mn 3+. The temperature shift between the TL signal and its corresponding PTTL signal is a consequence of the absence of P 2 after u.v. irradiation. The absence of P 2 is a result of the further phototransfer from P 2, to the lower temperature peak, which is unstable above room temperature rather than insensitive to u.v. irradiation. A plausible COSL mechanism is also presented in this investigation.

Thermoluminescence of Hydroxyapatite Doped with Copper

Abstract Thermoluminescence (TL) of hydroxyapatite, Ca5(PO4)3OH (abbreviated as OHAP) has been investigated by several authors, because this material is a main constituent of human bones. The samples showed two main TL peaks at about 110 and 150 oC by heating them at a rate of 20 oC.min-1 after X irradiation at RT. In order to use the TL glow peaks for dosimetry, it is desirable to intensify the 150 oC peak by the addition of activators, if possible, because the 110 oC peak is unstable under storage at RT after the irradiation. It was found that the OHAP doped with 0.03 wt% CuO showed about five times more intense a TL peak at 150 oC than the undoped one for an X irradiation of 0.465 C.kg-1, while the peak at about 110 oC decreased slightly. It was noted that a new TL peak was observed at 340 oC in OHAP:CuO. The 340 oC TL peak may also be suitable for the purpose.

Oxygen-evolving system and secondary quinonic acceptors are highly reduced in dark adapted Euglena cells: A thermoluminescence study

Characteristics of thermoluminescence glow curves were compared in three types of Euglena cells: (i) strictly autotrophic, Cramer and Myers cells; (ii) photoheterotrophic cells sampled from an exponentially growing culture containing lactate as substrate repressing the photosynthetic activity; (iii) semiautotrophic cells, sampled when the lactate being totally exhausted, the photosynthesis was enhanced.In autotrophic and semiautotrophic cells, composite curves were observed after series of two or more actinic flashes fired at -10°C, which can be deconvoluted into a large band peaking in the range 12-22°C and a smaller one near 40°C, This second band presents the characteristics of a typical B band (due to S2/3QB (-) recombination), whereas the first one resembled the band, shifted by -15-20°C, which is observed in herbicide resistant plants. The amplitude of this major band, which was in all cases very low after one flash, exhibited oscillations of period four but rapidly damping, with maxima after two and six flashes. In contrast, photoheterotrophic Euglena displayed single, non-oscillating curves with maxima in the range 5-10°C.In autotrophic and semiautotrophic cells, oxidizing pretreatments by either a preillumination with one or more (up to twenty-five) flashes, or a far-red preillumination in the presence of methylviologen, followed by a short dark period, induced thermoluminescence bands almost single and shifted by +3-5°C, or +12°C, respectively. In autotrophic cells, far-red light plus methyl viologen treatment induced a band peaking at 31°C, as in isolated thylakoids from Euglena or higher plants, while it had barely any effect in photoheterotrophic cells.Due to metabolic activities in dark-adapted cells, a reduction of redox groups at the donor and acceptor sides of PS II dark-adapted cells is supposed to occur. Two different explanations can be proposed to explain such a shift in the position of the main band in dark-adapted autotrophic control. The first explanation would be that in these reducing conditions a decreasing value of the equilibrium constant for the reaction: SnQA (-)QB⇌SnQAQB (-), would determine the shift of the main TL band towards low temperatures, as observed in herbicide resistant material. The second explanation would be that the main band would correspond to 'peak III' already observed in vivo and assigned to S2/3QB (2-) recombinations.

Progress in Thermoluminescence Dosimetry at the Institute of Nuclear Sciences, Vinca

Abstract Results are presented on: development of a new MgB4O7 thermoluminescence material with the main TL peak at about 270 oC with extremely stable TL characteristics; improvement of TL sensitivity of graphite-mixed MgB4O7:Dy TL detectors for beta dosimetry; preparation of LiF:Mg,Ti TL dosemeters in the form of sintered pellets, by a simplified preparation method; preparation of thermoluminescent lithium borates doped with manganese or copper, in the form of sintered pellets; production of unique sintered CaSO4:Dy TLD pellets developed at the Institute Vinca. The properties of these TL dosemeters, including sensitivity, reusability and storage characteristics, are presented.

5.5 eV optical absorption, supralinearity, and sensitization of thermoluminescence in LiF TLD-100

The concept of competition-during-heating as a mechanism for TL supralinearity and sensitization in TLD-100 is re-examined. It is demonstrated that with this model it is not necessary that the competing traps be removed by radiation in order for supralinearity to be obtained. Furthermore, the arguments for and against the proposal that the precursors to the 5.5 eV centers are the required competing centers are reviewed. It is shown that those experiments which are cited as arguments against this proposal have other interpretations different from those published so far. These new interpretations are consistent with the original view that the 5.5 eV centers’ precursors are indeed competitors to the main TL process. MgOH centers are also likely competitors in samples with substantial OH contents.

Comparative Dosimetric Studies of Three LiF TL Phosphors

A comparative dosimetric study has been done on three low Z TL phosphors: LiF TLD-100, LiF (Mg,Cu) and LiF (Mg,Cu,P). The main TL (dosimetric) peak occurs at almost the same temperature (~205 oC) in all these phosphors. The relative TL sensitivities (peak height method) to 60Co gamma rays of LiF TLD-100, LiF (Mg,Cu) and LiF (Mg,Cu,P) were found to be 1, 3.3 and 25.4 respectively. Using our TLD reader system, the respective minimum measurable gamma ray doses were estimated to be 51, 34 and 4.6 µGy. The effect of different thermal treatments on the TL sensitivity was also studied.

ESR and TL age determination of caliche nodules

Feasibility of dating caliche nodules by ESR and TL is investigated. For both methods the properties of the dating signal are described. Chemical composition as well as TL glow curves of caliches originating from different localities exhibit some differences. Due to the complexity of the TL glow curves, some samples required a special post-annealing procedure in order to resolve the main TL peak for age determination. Typical ESR calcite signals do not exist in caliche, therefore usefulness of the g = 2.0040 ESR signal is studied. The results of TL and ESR ages are found to be compatible except for two samples. Possible causes of the discrepancy in these samples are discussed. It is shown that, with proper treatment of the radiation-induced signals, it was possible to date caliche formations older than 350 ka, which is not achieveable with other methods like uranium series disequilibrium and/or radiocarbon dating.

Recombination luminescence in reactor and 14 MeV neutron irradiated Al 2O 3

Thermoluminescence is related to the F-center annealing in high purity α-Al 2O 3 irradiated with reactor neutrons (at 15, 360 K) and 14 MeV neutrons (near 300 K). In any case, the main TL emission spectrum consists of the intrinsic luminescence.

Phototransfer-thermoluminescence (PTTL) characteristics of mineral epidote

Abstract An investigation of phototransfer-thermoluminescence (PTTL) in epidote crystals has been carried out, using a broad-band u.v. source. The correlation between PTTL and possible anomalous fading of the high temperature (> 500°C) TL glow intensity has been studied by measuring the PTTL-induced low-temperature (> 500°C) peak height in samples which had been stored at room temperature for varying lengths of time following thermal drainage of TL from traps up to 500°C and before u.v. exposure. The results indicate that there is no noticeable fading of latent TL from deep traps for storage times of up to 3 months prior to the u.v. exposure. It may therefore be possible to employ the PTTL technique for purposes such as dating, instead of using the main TL peak (∼270°) in epidote, which is subject to anomalous fading.

Electron and hole centres produced in zircon by X-irradiation at room temperature

Radiation effects of X-rays in zircon (ZrSiO4) single crystals were studied at RT, by analysing the kinetics and spectrum of the thermoluminescence between 20 degrees and 420 degrees C. The results indicate that some of the electrons produced by the irradiation are captured by Dy3+ impurities apparently substituting for Zr4+ ions, while others are trapped at Si4+ lattice ions. The hole traps include O2- lattice ions near Si3+ or Dy2+ electron centres, as well as other unidentified impurities or point defects. A TL peak at 77.5 degrees C which consists of a broad emission band around 385 nm typical of the SiO44- group is ascribed to the recombination of an electron and a hole trapped at adjacent Si4+ and O2- ions respectively. Its measured activation energy (0.89 eV) is in agreement with the theoretical value (0.87 eV). A series of TL peaks having activation energies of 0.82-1.60 eV and showing the spectral lines of Dy3+ are attributed to electron-hole recombinations at the RE site. The main TL peak at 109 degrees C (E=1.18 eV), which contains both the 385 nm band and the Dy3+ lines, might involve a recombination process which excites both the SiO44- group and the RE ion.

ChemInform Abstract: THERMOLUMINESCENCE AND F‐CENTER ANNEALING IN ALKALINE‐EARTH FLUORIDE CRYSTALS AFTER REACTOR IRRADIATION AT LOW TEMPERATURE

Thermoluminescence is related to the F‐center annealing stage in undoped alkaline‐earth fluoride (CaF2, SrF2, and BaF2) single crystals irradiated at 20 K with reactor neutrons. The temperature of glow peak maxima are classified in four groups (P‐1–4); P‐1: 110–130 K, P‐2: 134–152 K, P‐3: 183–200 K and P‐4: 201–245 K with a heating rate of 4 K/min. at temperatures ranging 77–300 K. These temperatures of peak maxima correspond well to decay stages of F‐centers. F‐centers play an important role as recombination centers in the TL process. The main TL emission spectrum of P‐1–4 peaks consists of the intrinsic luminescence as well as the case of the x‐ray emission spectrum at 77 K. It is revealed that these TL emission bands near 300 nm of P‐1, 2, and 3 peaks are due to the radiative recombination of (VK+F) and (H+F) reactions, respectively.

Thermoluminescence and F-center annealing in alkaline-earth fluoride crystals after reactor irradiation at low temperature

Thermoluminescence is related to the F-center annealing stage in undoped alkaline-earth fluoride (CaF2, SrF2, and BaF2) single crystals irradiated at 20 K with reactor neutrons. The temperature of glow peak maxima are classified in four groups (P-1–4); P-1: 110–130 K, P-2: 134–152 K, P-3: 183–200 K and P-4: 201–245 K with a heating rate of 4 K/min. at temperatures ranging 77–300 K. These temperatures of peak maxima correspond well to decay stages of F-centers. F-centers play an important role as recombination centers in the TL process. The main TL emission spectrum of P-1–4 peaks consists of the intrinsic luminescence as well as the case of the x-ray emission spectrum at 77 K. It is revealed that these TL emission bands near 300 nm of P-1, 2, and 3 peaks are due to the radiative recombination of (VK+F) and (H+F) reactions, respectively.

Changes in the main TL glow peak of γ-irradiated CaSO 4: Dy phosphors after isothermal annealing

The effects of isothermal annealing, at various temperatures and for the same time, on the main TL glow peak of 60-Co γ-irradiated CaSO 4: Dy phosphors are described. Changes in the glow curve shape and shifts of the peak temperature are observed: the higher the annealing temperature, the higher the peak temperature. The experimental results are compared with those calculated by the continuous distribution of trap depths proposed by us in previous work. The agreement is fairly satisfactory.