TL Readout Research Articles

Flow synthesized LiBaF3 nanocubes as a promising optically stimulated luminescence phosphor

Integrating dosimeters are used in fields like personal dosimetry and radiotherapy quality assurance. Nanoparticles of LiBaF3 have been synthesized using a low-cost, high-throughput flow-synthesis setup and are found to be crystallographically phase-pure. Their radioluminescence (RL) emission shows three peaks corresponding to core-valence-band luminescence, self-trapped-exciton luminescence, and possibly impurity-related violet emission. Optically- and thermally stimulated luminescence (OSL and TL, respectively) overlap spectrally and show only the low-energy violet band, indicating a common luminescence pathway. The rapidly read-out OSL signal is linear in dose up to ∼1 kGy. The main TL glow peak, found around 120∘C, is depleted by optical stimulation, and similarly the OSL signal disappears following a TL readout. The thermal trap depth is found by the peak position method to be ∼1 eV. The high OSL light yield and reasonable fading of the nanoparticles qualifies them as an excellent candidate for OSL dosimetry.

DEMONSTRATION OF THE POTENTIAL AND DIFFICULTIES OF COMBINED TL AND OSL MEASUREMENTS OF TLD-600 AND TLD-700 FOR THE DETERMINATION OF THE DOSE COMPONENTS IN COMPLEX NEUTRON-GAMMA RADIATION FIELDS.

The results reported herein demonstrate the potential application of combined optically stimulated luminescence/thermoluminescent (OSL/TL) measurements in neutron-gamma discrimination dosimetry. The advantages of OSL/TL are two-fold: (i) The OSL and TL readout can be carried out on the same sample and (ii) the greater efficiency of OSL to high ionization density radiation due to F 2 and F3 excitation. The gamma/electron calibration coefficients for LiF:Mg, Ti (TLD-600 and TLD-700) were measured using a 90Sr/90Y source calibrated at the SARAF-SSDL nuclear facility. The estimation of the neutron calibration coefficients was carried out by irradiation with broad-spectrum beam of fast neutrons with median energy 5MeV at the Radiological Research Accelerator Facility (RARAF) of Columbia University. Naturally cooled samples of TLD-600 and TLD-700 were dosed to levels of 29.8Gy neutrons and 6.1Gy gammas in air and KERMA calculations employed to transfer the levels of dose to6,7LiF. A figure of merit for fast-neutron/gamma ray discrimination was determined at 10.6 for TLD-700 in the current measurements. The use of combined TLD-600/TLD-700 allowed, as well, the determination of a considerable and somewhat unexpected thermal neutron component of 116Gy in TLD-600.

Trap creation, trap conversion and thermoluminescence process in barite – effect of flux

ABSTRACT Among the undoped metal sulfates, on sintering at high temperatures, only BaSO4 was found to exhibit TL glow peaks in the region of radiation dosimetric interest i.e. ∼200°C (peak I) and 250°C (peak II). The TL intensity of peak I is very weak in purified BaSO4 but increased 4 times on 500°C, 1 h sintering. The intensity of peak II and the peak II/I height ratio increased with sintering temperature between 500°C and 1000°C. NaCl flux enhances the TL sensitivity of BaSO4 unlike that of Na2SO4. TL response of BaSO4 is in general linear below 1 kGy but unlike other phosphors, the TL response in the high dose region (> 1 kGy) does not saturate but increases sublinearly with dose (1–15 kGy) as a result of slow creation of traps by radiolysis. XRD shows that BaSO4 made with NaCl flux corresponding to a single phase of orthorhombic Barite crystal. The oxygen interstitial ions, are envisioned to be the hole traps and the radicals/anion vacancies formed by thermal dissociation of ions constitute the electron traps for peaks I and II, respectively. During TL, in the absence of dopants, the electron–hole recombination energy is observed under relaxed anion exciton emission in the 380–410 nm region. The phosphor is reusable after irradiation and TL readout. High dose irradiations, however, causes sensitization of TL after 400°C, 1 h post-irradiation anneal but a 700°C, 1 h anneal reduced the TL sensitivity. The creation of TL traps causing peak I precede that of peak II and a trap conversion between them occurs during high-temperature sintering. The study thus reveals for the first time that the defects causing TL peaks I and II are both thermally induced. Further studies to extend the saturation dose limit are proposed.

Thermoluminescence of Novel Zinc Oxide Nanophosphors Obtained by Glycine‐Based Solution Combustion Synthesis

High‐dose thermoluminescence dosimetry properties of novel zinc oxide nanophosphors synthesized by a solution combustion method in a glycine‐nitrate process are presented for the very first time in this work. Sintered particles with sizes ranging between ~500 nm and ~2 μm were obtained by annealing the synthesized ZnO at 900°C during 2 h in air. X‐ray diffraction patterns indicate the presence of the ZnO hexagonal phase, without any remaining nitrate peaks observed. Thermoluminescence glow curves of ZnO obtained after being exposed to beta radiation consists of two maxima: one located at ~149°C and another at ~308°C, the latter being the dosimetric component of the curve. The integrated TL fading displays an asymptotic behavior for times longer than 16 h between irradiation and the corresponding TL readout, as well as a linear behaviour of the dose response without saturation in the studied dose interval (from 12.5 up to 400 Gy). Such features place synthesized ZnO as a promising material for high‐dose radiation dosimetry applications.

Characterization of the burning conditions of archaeological pebbles using the thermal sensitization of the 110 °C TL peak of quartz

The 110 °C TL glow peak of quartz has been used in dating and retrospective dosimetry due to the pre-dose effect and the sensitivity changes caused by heating. One of the main difficulties related to TL dating is the sureness that the geological signal was completely zeroed by firing. In this study, the sensitivity change of the 110 °C peak and the EPR signal intensity of the E1′ center were combined to account for the burning status of archaeological pebbles. For this, a quartz pebble was sawn into many pieces and each piece was heat-treated at different temperatures from 200 to 800 °C. Powdered aliquots were γ-irradiated and stored into an ice-bath before the TL readout. Peak-maximum temperature, TL intensity and activation energy of the 110 °C peak were determined by glow curve deconvolution methods. The thermal activation characteristic obtained in this study showed a peak maximum at 500 °C and a sensitization ratio higher than 200. The heating temperature also affected the intensity of the E1′ center. The usefulness of the burning pattern was tested by measuring the TL and EPR signals of several archaeological pebbles, initially classified as “burnt”, “unburnt” or “unidentified”, and also from two specimens burnt in a campfire. The main achievement of this study was the possibility to infer the temperature in which a pebble was heated in the past independent of visual signs.

The applicability of the PTTL dose re-analysis method to the Harshaw LiF:Mg,Cu,P material

The phototransferred thermoluminescence (PTTL) technique is applied to the Harshaw LiF:Mg,Cu,P material. It is demonstrated that using 254-nm UV light, dose levels as low as 0.2 mGy can be re-estimated. The PTTL efficiency was found to be ∼ 6 % in the dose range of 0.2 mGy-1 Gy, and it appears to be dose-independent. This implies that a simple calibration factor could be applied to the PTTL data for the re-estimation of dose levels. It was demonstrated that with a proper choice of the TL readout parameters, and the UV-light irradiation conditions, dose levels that are relevant to personal or environmental dosimetry can be re-estimated.

A method of identification of abnormal glow curves in individual monitoring using CaSO4:Dy Teflon TLD and hot gas reader

In the present study, a method of identifying abnormal glow curves to electronically screen the glow curves of TL readout is presented. The method is based on the fact that the shape of an abnormal glow curve differs from the shape of a normal one. A few criteria for defining the normal shape of glow curves are arrived at by analysing the glow curves of dosemeters exposed to various doses in laboratory conditions and read at different elapsed time post irradiation. About 300 glow curves of dosemeters used for monthly monitoring were analysed as per these criteria and the effectiveness of the method is observed for total counts as low as 150 µSv equivalent.

Optimization of preparation procedure of LiF:Mg,Cu,Si TLD for improving the reusability

Several thermal treatments in the temperature range from 270 °C to 320 °C (each of 10 min) were tested as a final preparation procedure of LiF:Mg,Cu,Si to improve the protocol of TL readout with less residual signal for the LiF:Mg,Cu,Si TLD. This high sensitivity LiF:Mg,Cu,Si TLD exhibited thermal stability much better than that of the well known LiF:Mg,Cu,P. For LiF:Mg,Cu,Si, a readout temperature up to 300 °C did not affect the TL sensitivity and glow curve structure for 12 cycles of exposure and readout following an initial thermal treatment at 295 °C for 10 min. The residual TL signal also remained negligible.

Thermoluminescence of Vanadium–Doped SiO2 Synthesized by a Sol-Gel Method

AbstractThermoluminescence (TL) properties of pulverized SiO2:V monoliths synthesized by a solgel method, and annealed at 1273 K during 12 h under air, are presented in this work. Characteristics TL glow curves display a complex shape with at least three maxima located at ˜379, ˜543 and ˜591K. The TL total signal exhibited a linear behavior for doses below 400 Gy. The integrated TL fades down 26 % after 3 h elapsed between irradiation and the corresponding TL readout. These results lead to conclude that annealed SiO2:V is a promising material for ionizing radiation detection and dosimetry.

Investigation of OSL signals from very deep traps in unfired and fired quartz samples

This paper presents an attempt to isolate experimentally optically stimulated luminescence (OSL) signals which may originate from very deep traps (VDT) in quartz samples. As VDT we consider those traps which are responsible for TL glow peaks with a peak maximum temperature above a TL readout temperature of 500 °C. The basic experimental procedure used to isolate OSL signals from VDT is heating the quartz samples to 500 °C immediately before measuring the OSL signal. The study was carried out on eight quartz samples of very different origins; it is found that all eight samples exhibit OSL signals from VDT, and for a wide region of OSL stimulation temperatures. The OSL signal from VDT depends strongly on the type of quartz sample studied and on whether the sample was fired at high temperatures or not. The behavior of the OSL signal from VDT as a function of the stimulation temperature is found to be very different in fired and unfired samples. The thermal activation energy E for the OSL signals from VDT is obtained in both fired and unfired samples. The OSL signal from VDT in quartz samples fired at 800 °C for 1 h is very high, and the OSL curves consist of three well-defined components and a fourth slow component which is rather poorly resolved. The dose response of these components is obtained using a computerized deconvolution procedure for the dose region 0.5–300 Gy. The results are of importance for dating of ancient fired ceramics, since OSL signals from VDT could potentially extend appreciably the equivalent dose region toward both lower and higher values.

Preliminary design of a single sphere multidetector directional neutron spectrometer using TLD-600

This communication summarizes the preliminary results obtained for the design of a neutron spectrometer based on thermoluminiscent 6LiF:Ti,Mg (TLD-600) dosimeters located along three perpendicular axis within a single polyethylene sphere. The neutron response functions have been calculated using the Monte Carlo (MC) code MCNPX 2.5 for different incidence directions. The applicability of the device has been investigated, relying on simulated exposures to reference fields of 241Am-Be and bare 252Cf, using the MAXED, GRAVEL and FRUIT unfolding codes. Moreover, a sensitivity analysis with FRUIT has been performed to evaluate the influence of the TL readout uncertainties on the results of the unfolding process.

WE‐E‐BRA‐07: Experimental Determination of the LiF:Mg,Ti TLD Energy Response Correction Factor for 125I Brachytherapy Sources

Purpose: To further explore the energy response correction factor for LiF:Mg,Ti thermoluminescent dosimeters for use in experiments with low dose rate brachytherapy sources. Method and Materials: Two distinct experiments were performed to determine the value of the energy response correction factor, E(r), as defined in TG‐43U1, for seeds. The University of Wisconsin Variable Aperture Free Air Chamber was used to determine the air kerma strengths of Best Medical 2301 seeds. A 3×3 array of TLD‐100 chips sealed in a thin plastic bag was attached to the center of the aperture using Kapton tape. was used to irradiate a set of comparison TLDs to a dose to water equivalent to the dose to water given by . Monte Carlo simulations were used in both cases to calculate the dose to water from the measured air kerma. The two experiments had different annealing techniques: one using a standard anneal of one hour at 400°C followed by 24 hours at 80°C, and the other using a standard anneal at the beginning of the sorting process and then only the 80°C anneal between cycles. Results: E(r) was determined to be 1.514 ± 0.019 using the 80°C technique and 1.549 ± 0.025 using the standard technique. These values are significantly higher than the currently applied value of 1.41, but not unexpected. TG‐43U1 noted that the work of Davis et al. also observed an anomalous over‐response relative to theoretical predictions. It is speculated that the differences between these two experimental values may be the result of the annealing techniques and TL readout characteristics, which will be further investigated. Conclusion: It appears that LiF:Mg,Ti TLDs are indeed intrinsically non‐linear in their response to low energy photons. The solid state processes that cause this effect are not taken into account by Monte Carlo.

An alternative method of preparation of dosimetric grade α-Al 2O 3:C by vacuum-assisted post-growth thermal impurification technique

Single-crystal α - Al 2 O 3 (10×10 mm 2,0.4 mm thick) was treated in vacuum at temperatures below its melting point in the presence of graphite. The possibility of this approach as an alternative method to the crystal growth in the reduced atmosphere for obtaining dosimetry grade α -Al 2O 3:C for TL and OSL dosimetry applications has been explored. The absorption peaks at 203, 225, and 255 nm in the treated sample confirmed the formation of negative ion vacancy in the crystalline α-Al 2O 3. The TL readout of the processed samples showed two well-defined glow peaks at 56°C and 191°C for a 4 K/ s heating rate. The TL and OSL sensitivities of the samples were seen to strongly depend on process temperature and process time and are comparable to those produced by conventional method. The OSL response of these samples is found to be linear from 50 μGy to 1 Gy . The results show that, with this approach, it is possible to introduce the desired dosimetric traps into crystalline α-Al 2O 3 in a controlled manner.

Effect of heating rate on the responses of CaF2:Cu, CaF2:Tm, CaF2:Dy and CaF2:Mn.

Recent development of CaF2:Cu (the most sensitive material for radiation dosimetry) exhibiting a TL glow peak around 270 degrees C similar to that of CaF2:Mn has made it attractive to study the influence of heating rate on the response of CaF2 based TLDs. Influence of heating rate on CaF2:Mn (known to reduce the response with increasing heating rate) was confirmed in view of the reported controversy about other TLDs. Responses of TL glow peaks around 270 degrees C in CaF2:Cu, CaF2:Tm, CaF2:Dy and CaF2:Mn were studied. Except CaF2:Mn, no other CaF2 based TLD exhibited a reduction in response with increasing heating rate. On the contrary, in some cases a small increase (10-15%) was noted with increasing heating rate from 1 degrees Cs(-1) to 50 degrees Cs(-1). The shape and the position of the glow peak and the parameters derived from the shape of the glow curve appear to have no relation to reduction of TL efficiency at higher heating rates. Apart from the increased probability of non-radiative transitions at higher temperatures, the observed effects have been assigned to the effect of heating rate on the migration of charge carriers released during the TL readout.

Extending the time range of luminescence dating using red TL (RTL) from volcanic quartz

The potential of red thermoluminescence (RTL) emission from quartz, as a dosimeter for baked sediments and volcanic deposits, has received some attention over the past decade. While there have been some important observations relating to signal stability, saturation characteristics and emission wavebands, there has not been a systematic analysis of RTL properties of older (i.e., >1 Ma), quartz-bearing known age volcanic deposits. We have undertaken such an analysis using independently-dated silicic volcanic deposits from New Zealand, ranging in age from 300 ka through to 1.6 Ma. We observed a complex RTL emission in most volcanic quartzes, which consists of a number of discrete high temperature (i.e, >220°C) TL peaks. Isothermal analysis indicates a stable dating trap ( E=2.03 eV; S=4.20×10 15) which is stable at ambient (c. 20°C) temperatures for >10 9 a. We confirm the slow onset of saturation with dose, and the limited extent of sensitivity changes due to dosing and TL readout. As such, there is much potential for exploiting the dosimeter in dating studies and we present the results from a modified single aliquot regenerative (SAR) procedures which indicate that there is a good agreement between RTL dating and other methods over time scales 10 5–10 6 a. This paper presents a summary of the most important related results of our findings and outlines the configuration of photomultiplier and filter combinations which maximizes RTL detection for temperatures up to 500°C.

Characterization of Fundamental Luminescence Properties of the Mars Soil Simulant JSC Mars-1 and Their Relevance to Absolute Dating of Martian Eolian Sediments

This report explores the potential for luminescence dating techniques to provide absolute age determinations of eolian sediments on the surface of Mars, including those incorporated in the martian polar ice caps. Fundamental thermally and optically stimulated luminescence properties of bulk samples of JSC Mars-1 soil simulant are reported and their relevance to the development of dating procedures is discussed. The radiation-induced luminescence signals (both thermoluminescence, TL, and optically stimulated luminescence, OSL) from JSC Mars-1 are found to have a wide dynamic dose–response range, with the luminescence increasing linearly to the highest doses used (936 Gy), following irradiation with 90Sr/ 90Y beta particles. The signals are also susceptible to solar resetting, with the OSL signals decreasing to <10% of their original levels within the first 20 min of exposure to sunlight. The TL signal also decays rapidly, being reduced to ∼15% within the first 20 min, but reaches a stable, nonzero level at long bleaching times. Neither the TL nor the OSL signals exhibit fading (i.e., loss of signal after irradiation before TL or OSL readout), nor do they exhibit significant sensitivity changes upon repeated irradiation and readout. These three properties (wide dynamic range, solar bleaching, and signal stability) form a stable base for future investigation of the material for luminescence dating and form a preliminary step toward development of dating protocols for terrestrial analogs of Mars surface materials. We conclude that luminescence dating, properly developed, holds the potential to be a valuable tool for absolute dating of martian eolian sediments

PTTL Dose Re-estimation Applied to Quality Control in TLD-100 Based Personal Dosimetry

A new method for quality control of dose performance in Personal Dosimetry using TLD-100 is presented. This method consists of the application of dose reassessment techniques based on phototransferred thermoluminescence (PTTL). Reassessment is achieved through a second TL readout of the dosemeters worn by the controlled workers, after a reproducible UV exposure. Recent refinements in the PTTL technique developed in our laboratory allow reassessing doses as low as 0.2 mSv, thus extending the reassessment capability to the entire dose range that must be monitored in personal dosimetry. After a one month exposure, even purely environmental doses can be reassessed. This method can be applied for either re-estimation of single doses or of the total dose accumulated after a number of exposures and dose measurements. Several tests to reconfirm low doses in normal working conditions for personal dosimetry have been performed. Each test consisted of several cycles of exposure and TL evaluations and a final PTTL re-estimation of the total accumulated dose in those cycles. The results obtained always showed very good agreement between the sum of the partial doses and the total reassessed dose. The simplicity of the method and the possibility of re-evaluating the doses assessed to the workers employing their own dosemeters are advantageous features to be considered in designing systems for the determination of real performance in personal dosimetry.

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.

An analytical method for the thermoluminescence growth curve and its validity

The radiative recombination probability P of a carrier released from an active TL trap is computed for the case when the TL traps are interactive with the deep traps. It is shown that the value of P remains constant throughout the TL readout heating when the capture coefficients of the recombination centre and the deep trap are equal. When these coefficients are not equal, P undergoes change but its variation with temperature is still insignificant under a wide variety of conditions. A net value P applicable to the area of the glow curve is calculated and compared with the initial (when heating is begun) value of P, which is used in the analytical expression for the area of the glow curve.

A TLD Method for Evaluation of Radiation Quality and Measurement of Entrance Skin Dose from Diagnostic X Ray Practices

A TLD method based on CaSO4:Dy Teflon discs has been developed for the evaluation of radiation quality and measurement of entrance skin absorbed doses to estimate the effective dose equivalent to the population from diagnostic X ray practices. The method is particularly useful in carrying out large scale measurements at distant diagnostic installations by mailing a set of dosemeters. While the TLD discs in thin polyethylene pouches act as dosemeters for the measurement of entrance skin absorbed dose in any X ray examination, these discs in a specially designed holder measure the quality (half-value thickness, HVT) of the X ray beam. The entrance skin absorbed dose measurement is based on the fact that the TLD discs exhibit a high sensitivity and photon energy independent response (within ±10%) to diagnostic X ray beams, whereas the estimation of the quality of X ray beams is based on the change in the ratio of the TL readout of discs under a 1 mm Cu filter and 0.5 mm of plastic in the holder. The change in the TL readout ratio is about 3 times that of the change in the HVT measured by a conventional method using an ion chamber detector and aluminium absorber under narrow beam geometry, and hence offers a sensitive method for the estimation of the quality of an X ray beam without having prior knowledge of tube parameters. The output of an X ray machine is measured from the readout of the discs under a 0.5 mm thick plastic sheet in the holder.