Accidental gamma dose measurement using commercial glasses

Commercial glasses have been investigated for their application in accidental gamma dose measurement using Thermoluminescent (TL) techniques. Some of the glasses have been found to be sensitive enough that they can be used as TL dating material in radiological accident situation for gamma dosimetry with lower detection limit 1 Gy (the dose significant for the onset of deterministic biological effects). The glasses behave linearly in the dose range 1-25 Gy with measurement uncertainty +/- 10%. The errors in accidental dose measurements using TL technique are estimated to be within +/- 25%. These glasses have shown TL fading in the range of 10-20% in 24 h after irradiation under room conditions; thereafter the fading becomes slower and reaches upto 50% in 15 d. TL fading of gamma-irradiated glasses follows exponential decay pattern, therefore dosimetry even after years is possible. These types of glasses can also be used as lethal dose indicator (3-4 Gy) using TL techniques, which can give valuable inputs to the medical professional for better management of radiation victims. The glasses are easy to use and do not require lengthy sample preparation before reading as in case of other building materials. TL measurement on glasses may give immediate estimation of the doses, which can help in medical triage of the radiation-exposed public.     

Theoretical modelling of experimental diagnostic procedures employed during pre-dose dosimetry of quartz

The pre-dose technique in thermoluminescence (TL) is used for dating archaeological ceramics and for accident dosimetry. During routine applications of this technique, the sensitisation of the quartz samples is measured as a function of the annealing temperature, yielding the so-called thermal activation characteristic (TAC). The measurement of multiple TACs and the study of the effect of UV-radiation on the TL sensitivity of quartz are important analytical and diagnostic tools. In this paper, it is shown that a modified Zimmerman model for quartz can successfully model the experimental steps undertaken during a measurement of multiple TACs.     

Tunnelling in afterglow,its coexistence and interweaving with thermally stimulated luminescence

After irradiation of a phosphorescent material, the intensity of the afterglow is usually strongly dependent on the temperature: as lower temperatures are reached, it drops below the noise. But sometimes this intensity stops dropping and becomes stationary. It is seen then to decrease slowly with the time t with (1/t) kinetics. This odd emission is shown to compete with the regular TL or OSL by involving the same traps and centres. It is proposed that in this process the trapped charges recombine with centres without thermal excitation by tunnelling through a potential barrier. The parasitical effect of anomalous fading in radiation dosimetry and dating, with its experimental logarithmic law of loss of stored TL, is shown to be explained by this tunnelling. This effect, together with widening of TL peaks, turns up in samples which have less perfect or disordered crystal lattices.     

The chernobyl fallout in Greece and its effects on the dating of archaeological materials

The effects of the fallout from the nuclear reactor accident at Chernobyl have been monitored at various sites in Greece. Here we present the first estimates of gamma dose rates, an essential parameter in the dating of archaeological materials by thermoluminescence (TL) and ESR methods.

The dose rates are derived from the long-lived radionuclides of ¹³⁷Cs, ¹³⁴Cs, ¹⁰⁶Ru and ¹⁴⁴Ce (with ).

The present dose rates vary between 30 and 60 mrad/yr, but maximum values of around 811 mrad/yr have also been recorded, for ground-surface exposures.

These dose rate values must be regarded as very significant to TL and ESR dating of samples from now on and a correction factor should be applied.     

Luminescence quartz dating of lime mortars. A first research approach

Lime mortars mixed with sand are well suited for connecting structural materials, like stones and bricks, due to the mechanical properties this material exhibits. Their extensive use in architectural and decorative works during the last 4000 years motivated the introduction of the 'Luminescence clock' for age determination of mortars. The same principles as for quartz optically stimulated luminescence (OSL) dating of sediments were applied for age estimation of a mortar fragment removed from a Byzantine church monument dated by archaeological means to 1050-1100 years ago (the first half of the 10th century). The OSL from the quartz was monitored under blue light stimulation and UV detection, using a single-aliquot-regenerative-dose protocol. The quartz-OSL dating of the mortar resulted in 870 +/- 230 a. TL polymineral fine grain dating was also performed on a brick fragment which was connected to the mortar, resulting in a TL age of 1095 +/- 190 a.     

Thermoluminescence of cement

Cement is found to be a thermoluminescent material. The glow curves of ordinary portland cement obtained from two different sources are found to be qualitatively similar. White cement (J K Brand) exhibits intense thermoluminescence (TL) compared to Birla white brand. The emission of J K white cement seems to be mainly due to Mn impurities which enters the product through limestone, the major ingredient in the preparation of cement. The possible use of TL as a spectroscopic technique to characterize cement is discussed.     

Triboluminescent properties of zinc sulfide phosphors due to hypervelocity impact

The emission of light due to crystal fracture, or triboluminescence (TL), is a phenomenon that has been known for centuries. One of the most common examples of TL is the flash created from chewing Wint-O-Green Lifesavers^®. From 2004 to 2006, research was completed using the two-stage light gas gun located at the NASA Marshall Space Flight Center (MSFC) in Huntsville, Alabama to measure the TL properties for zinc sulfide doped with both manganese (ZnS:Mn) and copper (ZnS:Cu). Results clearly show that hypervelocity impact-induced TL has been observed for both ZnS:Mn and ZnS:Cu. For ZnS:Mn, TL produced during 4.7 and 5.7 km/s impacts was statistically more luminous than was observed from similar data collected at 3.3 km/s. The TL decay time for ZnS:Mn was found to be 292 ± 58 μs, which is totally consistent with earlier measurements that did not use impact as an excitation source. Further, the emission of TL from ZnS:Mn undergoing hypervelocity impact has been demonstrated to have a significant component at the known peak emission wavelength of ZnS:Mn of 585 nm. Small TL emission generated as a result of hypervelocity impact was also observed from ZnS:Cu. The most intriguing conclusion from this research is that it may be possible to discriminate impact velocity by measuring the time-integrated luminosity of TL phosphors. An ability to measure the velocity of a hypervelocity impact is a significant indicator of the potential usefulness for this concept for use as an impact sensor in future spacecraft.     

Development of LiF:Mg,Cu,Si TL material (new KLT-300) with a low-residual signal and high-thermal stability

LiF-based thermoluminescence (TL) materials have been widely used for radiation dosimetry due to their attractive features. LiF:Mg,Cu,P is one of the most sensitive tissue-equivalent TL materials, approximately 40 times more sensitive than LiF:Mg,Ti (TLD-100), but it has two main drawbacks: a thermal loss of the TL sensitivity when annealed at temperatures >240 degrees C, and a relatively high-residual signal. Recently, LiF:Mg,Cu,Na,Si TL material was developed to overcome these drawbacks at the Korea Atomic Energy Research Institute, but it provided only marginal improvements in reducing the residual signal. The newly developed LiF:Mg,Cu,Si TL material has a significantly lower residual signal and a better stability to thermal treatments. In this article, the preparation method and some dosimetric properties (sensitivity and residual signal) of the new LiF:Mg,Cu,Si TL material are presented. At the end of the preparation procedures, a dual-step annealing method is introduced and this has proved as a very efficient method to reduce the high-temperature peak and is the cause of residual signal. Therefore, the high-temperature peak in the glow curve was significantly reduced. The sensitivity is approximately 20 times higher than that of TLD-100 and the residual signal was estimated to be approximately 0.04%.     

Correlation between thermoluminescence and mechanoluminescence of γ-ray-irradiated Dy-doped BaB<Subscript>4</Subscript>O<Subscript>7</Subscript> phosphors

Undoped and dysprosium (Dy)-doped BaB₄O₇ phosphors have been synthesised by solid-state diffusion technique and its thermoluminescence (TL) and mechanoluminescence (ML) has been studied. A single peak at 162 °C along with two shoulders around 242 and 294 °C was observed in TL glow curve of undoped BaB₄O₇ phosphors. TL intensity increased with increasing dopant concentration and broad band was observed for the sample having 0.5 mol% of dopant concentrations. For higher concentration of dopant, concentration quenching occurred. ML has been excited impulsively by dropping a piston of mass 0.6 kg on the phosphors with various impact velocities. As the piston was dropped on to the sample, ML intensity initially increased with time attained an optimum value for a particular time then decreased and finally disappeared. ML intensity varied with dopant concentration and it has been obtained optimum for the sample having 0.5 mol% of dopant. TL and ML intensity increased with gamma doses given to the sample. ML intensity increased almost linearly with the impact velocity of the piston dropped on to the sample, however, time corresponding to ML peak shifted towards shorter time value with increasing impact velocity of the piston dropped on to it. ML emission spectrum showed characteristic emission of Dy³⁺ ions. In order to study the influence of deformation on TL, TL was recorded after deforming the sample by dropping the load on to it. When the TL was recorded after deforming the sample, it is found that TL yield decreased markedly and it further decreased with increasing the height of the piston from which it was dropped. Results suggest that though the mode of excitation is different in these two phenomena but similar states are responsible for TL and ML.     

Thermal pre-treatment in the OSL dating of quartz: is it necessary?

Thermal treatment before optically stimulated luminescence (OSL) measurement is an important step in all widely accepted OSL dating procedures used with quartz. This is a major constraint on the design of a portable luminescence instrument for estimating ages in the field. Preliminary experiments show that using a standard dating protocol without heating caused a 30-50% underestimation of equivalent dose. This underestimate arises mainly from OSL derived from the 110 degrees C thermoluminescence (TL) trap; because of the thermal instability of this trap, this OSL contribution is only present in unheated laboratory-regenerated signals, but not in the natural signal. An alternative to thermal pre-treatment is investigated, based on the mathematical separation of the stable dosimetry OSL signal from the total OSL; the latter is the sum of signals from several traps, including the 110 degrees C TL trap. Our results show consistency with dose estimates obtained using a standard measurement protocol including pre-heating.     

On the use of LiF:Mg,Ti thermoluminescence dosemeters in space--a critical review

The use of LiF:Mg,Ti thermoluminescence dosemeters (TLDs) in space radiation fields is reviewed. It is demonstrated in the context of modified track structure theory and microdosimetric track structure theory that there is no unique correlation between the relative thermoluminescence (TL) efficiency of heavy charged particles, neutrons of all energies and linear energy transfer (LET). Many experimental measurements dating back more than two decades also demonstrate the multivalued, non-universal, relationship between relative TL efficiency and LET. It is further demonstrated that the relative intensities of the dosimetric peaks and especially the high-temperature structure are dependent on a large number of variables, some controllable, some not. It is concluded that TL techniques employing the concept of LET (e.g. measurement of total dose, the high-temperature ratio (HTR) methods and other combinations of the relative TL efficiency of the various peaks used to estimate average Q or simulate Q-LET relationships) should be regarded as lacking a sound theoretical basis, highly prone to error and, as well, lack of reproducibility/universality due to the absence of a standardised experimental protocol essential to reliable experimental methodology.     

The identification of thin amorphous films at grain-boundaries in Al2O3

The presence of amorphous grain-boundary phases in ceramic materials can significantly influence their properties. Such grain-boundary films can be identified by the dark-field diffuse scattering technique, the Fresnel fringe technique, and analytical electron microscopy (energy-dispersive spectroscopy). However, spectrum artefacts can present major problems for the use of such techniques. Specifically, grain-boundary grooving, surface damage of the specimen and silicon contamination are shown experimentally to arise from ion-milling during the preparation of TEM specimens. It is experimentally shown that, with the above techniques, these artefacts can cause grain-boundaries in commercial alumina specimens to appear to contain glassy phases. The ambiguity in interpreting the results from the use of each of these techniques is discussed in detail.     

UV-induced bleaching of deep traps in Harshaw TLD LiF:Mg,Cu,P and LiF:Mg,Ti

The effects of UV-induced bleaching of deep traps on Harshaw thermoluminescent (TL) LiF:Mg,Cu,P and LiF:Mg,Ti materials were investigated. During a normal heating cycle, LiF:Mg,Cu,P is limited to a maximum temperature of 240 °C. LiF:Mg,Ti can be read to higher temperatures; however, encapsulation in polytetrafluoroethylene limits the maximum readout temperature to 300 °C. Generally, for both materials, these respective temperatures are sufficient for emptying traps corresponding to the main dosemetric peaks. However, when the dosemeters are subjected to a high dose level, such as 1 Gy (much higher than individual monitoring dose levels), higher temperature traps are filled that cannot be emptied without exceeding the above-mentioned maximum temperatures. These high temperature traps tend to be unstable during normal readout and can significantly increase the residual TL signal. The purpose of this study was to investigate the applicability of a UV-induced bleaching technique for emptying higher temperature traps following high-dose applications. In addition, in the case of LiF:Mg,Cu,P, where the maximum readout temperature is significantly lower, we investigated the possibility of reducing the residual signal using the application of repeated readout cycles. The optical bleaching approach was found to be effective in the case of LiF:Mg,Ti; however, for LiF:Mg,Cu,P, no reduction in the residual signal was observed. For this latter material, the application of repeatable readout cycles is very effective and residual signals equivalent to dose levels as low as 0.01 mGy were observed following an initial dose of 5 Gy. To the best of our knowledge, this work is the first attempt to apply an 'optical annealing' technique to the Harshaw thermoluminescent dosemeter (TLD) materials.     

Energy responses of the LiF series TL pellets to high-energy photons in the energy range from 1.25 to 21 MV

The energy responses for the KLT-300(LiF:Mg,Cu,Na,Si, Korea), GR-200(LiF:Mg,Cu,P, China) and MCP-N(LiF:Mg,Cu,P, Poland) thermoluminescence(TL) pellets were studied for a photon radiation with energies from 1.25 MeV(60Co) to 21 MV (Microtron) to verify the usefulness of the calibration for the radiotherapy beams. The International Atomic Energy Agency (IAEA) and the World Health Organization (WHO) have performed thermoluminescence dosimetry (TLD) audits to verify the calibration of the beams by TL powder, but TL pellets were used in this study because the element correction factor (ECF), defined as the factor to correct the variations that all TL dosemeters cannot be manufactured to have exactly the same TL efficiency, for each TL pellet could be accurately derived and be handled conveniently when compared with the powder. Also several works for the energy response of the TLDs were done for the low-energy photon beams up to 60Co, but they will be extended in this experiment to the high photon energies (up to 20 MV), which are widely used in the therapy level of a radiation. The PTW 30006 ionisation chamber was calibrated by the Korea primary standards to establish the air-kerma rates and the TL pellets were irradiated in a specially designed waterproof pellet holder in a water phantom (30 x 30 x 30 cm3) just like the IAEA postal audits programme. This result was compared with that of another type of phantom [10 (W) x 10 (L) x 10 (H) cm3 PMMA Perspex phantom for the 60Co and 6 MV photon, and 10 x 10 x 20 (H) cm3 for the 10 and 21 MV photon] for its convenient use and easy handling and installation in a hospital. The results show that the differences of the responses for the water phantom and PMMA Perspex phantom were negligible, which is contrary to the general conception that a big difference would be expected. For an application of these results to verify the therapy beams, an appropriate energy correction factor should be applied to the energies and phantom types in use.     

Experimental determination of the dose deposition profile of a 90Sr beta source

Three different methods for characterising the dose deposition profile of a (90)Sr/(90)Y radioactive source are described: GAFChromic film dosimetry, Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL). For the film measurements, GAFChromic film samples were stacked at different depths between polyethylene terephthalate (PET) foils. For TL, the thickness of a TLD-500 dosemeter was gradually reduced by polishing and the TL from chips of different thickness was used in conjunction with a mathematical model based on the exponential attenuation of dose inside the crystal to determine the decay constant for the dose-depth profile. Finally, an OSL reader with confocal stimulation / detection capabilities was used to map the two-dimensional dose distribution in TLD-500 dosemeters as a function of depth. The shapes of the dose deposition profiles obtained from all the investigated methods are in good agreement.     

The influence of post-exposure heating on the stability of MCP-N (LiF:Mg,Cu,P) TL detectors

Post-exposure annealing of highly sensitive LiF:Mg,Cu,P (MCP-N) detectors, at 100 degrees C over 10 or 20 min prior to readout, is usually recommended for routine dosimetry. The purpose of this anneal is to eliminate low-temperature peaks, especially peak 3, which fades at room temperature in about 3 months. However, as this annealing procedure does not entirely eliminate peak 3, 10% of its thermoluminescent (TL) signal still being readable, a fading correction must be applied. The aim of this work was to optimise the conditions of post-exposure treatment, i.e. its temperature and duration, in order to facilitate the use of MCP-N detectors in routine dosimetry. MCP-N detectors were annealed in standard conditions, i.e. at 240 degrees C over 10 min and exposed to a dose of 5 mGy (137Cs). For post-exposure annealing, six different temperatures between 100 degrees C and 150 degrees C and two time periods (10 and 20 min) were tested. TL glow curves were deconvoluted with the GCA code. A post-exposure anneal at 120 degrees C over 10 min was found to be optimal. Heating at this temperature eliminates 100% of the TL signal of peak 3, while maintaining the area and maximum intensity of the main peak 4 unchanged. In this case, no fading correction needs to be applied. Annealing at higher temperatures, up to 150 degrees C, results in a loss of peak 4 signal, and is therefore not recommended.     

Isotachophoresis in free-flow using a miniaturized device

For the first time, we report a miniaturized approach for isotachophoresis employing the technique of free-flow electrophoresis. Using a micromachined separation chamber with a volume of 200 nL, a sample mixture of fluorescein, eosin G, and acetylsalicylic acid was separated, stacked, and concentrated in less than a minute. Additionally, an isotachophoretic separation of a reaction mixture of myoglobin and fluoresceinisothiocyanate as a fluorescence label has shown the potential of this method for on-line sample preparation.     

In situ measurement on ultraviolet dielectric components by a pulsed top-hat beam thermal lens

A simple and sensitive mode-mismatched thermal lens (TL) technique with a pulsed top-hat beam excitation and a near-field detection scheme is developed to measure in situ the thermoelastic and the thermooptical responses of ultraviolet (UV) dielectric coatings as well as bulk materials under excimer laser (193- or 248-nm) irradiations. Owing to its high sensitivity, the TL technique can be used for measurements at fluences far below the laser-induced damage threshold (LIDT). We report on the measurement of both linear and nonlinear absorption of the UV dielectric coatings and bulk materials as well as the investigation of time-resolved predamage phenomena, such as laser conditioning of highly reflective dielectric coatings and irradiation-induced changes of a coating's various properties. The pulsed TL technique is also a convenient technique for accurate measurement of the LIDT of dielectric coatings and for distinguishing different damage mechanisms: thermal-stress-induced damage or melting-induced damage.     

Identification of static exposure of standard dosimetric badge with thermoluminescent detectors

There are three main methods used in individual monitoring: radiographic films, thermoluminescence (TL) and optically stimulated luminescence (OSL). Distinguishing between static (e.g. by leaving it accidentally or purposely in the radiation field) and dynamic exposures can be almost routinely performed for radiographic and OSL methods but is still unsolved for TL detectors. The main aim of this work is to develop a method for identifying static exposures of standard TL detectors at doses which are typical of radiation protection. For this purpose, a new TLD reader equipped with a CCD camera was developed to measure the two-dimensional signal map and not only the total light emitted (as is performed with standard photomultiplier-based TL readers). Standard MCP-N (LiF:Mg,Cu,P) TL pellets of 4.5 mm diameter and 0.9 mm thickness were installed in the standard Rados TL personal badges with special, non-uniform filters and exposed statically to 33 keV X-ray beams at three angles: 0 degrees , 30 degrees and 60 degrees . The detectors were readout in the CCD camera reader and 2-D images were collected. The analysis of these CCD images allows the identification of the static exposure cases and partly the angle of incidence at a dose level of 20 mSv.