A system to irradiate and measure luminescence at low temperatures

We have developed a system to irradiate samples and record radioluminescence (RL), optically stimulated luminescence (OSL), and thermoluminescence (TL) at temperatures ranging from -150 degrees C to 200 degrees C. The system consists of a cryostat, an irradiation/stimulation unit fitted with an X-ray tube (40 kV Moxtek) and a quartz window for optical stimulation, and a detection unit that utilises a photomultiplier tube and an interchangeable filter pack. Experiments have been conducted with quartz and albite (a feldspar). TL and OSL experiments show that several optically sensitive trapping states are stable below -50 degrees C. In addition, an increase in OSL is seen as the OSL stimulation temperature is lowered below -50 degrees C, and an increase in RL is apparent as the temperature is lowered during irradiation. This indicates that not only are optically sensitive low temperature traps present but that luminescence becomes more efficient at low temperatures.     

OSL and TL in LiF:Mg,Ti following alpha particle and beta ray irradiation: application to mixed-field radiation dosimetry

The optically stimulated luminescence (OSL) of LiF:Mg,Ti (TLD-100) following irradiation by beta and alpha particles was investigated by the measurement of the excitation and emission spectra of OSL and comparison with thermoluminescence (TL) characteristics. Measurements were also carried out on nominally pure LiF monocrystals. The preferential excitation of OSL compared to TL following high-ionisation density (HID) alpha irradiation is naturally explained via the identification of OSL with the 'two-hit' F2 or F3+ centre, whereas the major component of composite TL glow peak 5 is believed to arise from a 'one-hit' complex defect. This discovery allows near-total discrimination between HID radiation and low-ionisation density radiation and may have significant potential in mixed-field radiation dosimetry.     

Performance of CVD diamond as an optically and thermally stimulated luminescence dosemeter

Diamond is a material with extreme physical properties. Its radiation hardness, chemical inertness and tissue equivalence qualify it as an ideal material for radiation dosimetry. In the present work, the optically stimulated luminescence (OSL) and thermoluminescence (TL) characteristics of a 10 microm thick CVD diamond (polycrystalline diamond films prepared by chemical vapor deposition) film were studied in order to test its performance as a beta radiation dosemeter. The TL response is composed of four main TL glow peaks; two of these are in the range of 150-200 degrees C and two additional peaks in the 250-400 degrees C temperature range. The integrated TL as a function of radiation dose is linear up to 100 Gy and increases with increasing dose exposure. The dose dependence of the integrated OSL exhibits a similar behavior. The observed OSL/TL behavior for the CVD diamond film clearly demonstrate its capability for applications in radiation dosimetry with special relevance in medical dosimetry owing to the diamond's intrinsic material properties.     

Optical and dosimetric properties of zircon

Irradiation effects were investigated in zircon crystals by methods of optical absorption and luminescence. Special attention was given to the effects of vacuum ultraviolet (VUV) radiation. The same main thermoluminescence (TL) peaks with the same thermal activation energies appeared after VUV as after X- or beta irradiation, indicating that the same traps were induced by the different irradiations. TL excitation spectra in the VUV showed an increase <220 nm and maxima near 190 and 140 nm. Excitation spectra of phototransferred TL (PTTL) and optically stimulated luminescence (OSL) were also measured. Most TL emission bands also appeared in the X-luminescence, PTTL and OSL. Dosimetric properties such as the TL radiation sensitivity, thermal stability of radiation-induced defects and TL dose dependence were also investigated. The radiation sensitivity of zircon was by an order of magnitude lower than that of TLD-100. The 355 K TL peak showed linear dose dependence only up to approximately 500 Gy and the 520 K peak up to approximately 1800 Gy.     

Influence of the stem effect on radioluminescence signals from optical fibre Al2O3:C dosemeters

This paper analyses the influence of the Cerenkov radiation and other noise sources, the so-called stem effect, on radioluminescence (RL) signals generated in optical fibre Al2O3:C dosemeters used in medical dosimetry. The optical fibre dosemeter consists of a sensitive Al2O3:C crystal coupled to an optical fibre cable that carries the RL and optically stimulated luminescence (OSL) signals generated in the Al2O3:C crystal. During irradiation of the dosemeter, the real-time dose rate can be determined from the RL signal and after irradiation the total dose absorbed is determined from the OSL signal stimulated using a focused green solid-state laser. In particular, the components of the stem effect generated in the fibres were analysed to determine their impact on the RL signal.     

Optically stimulated luminescence dosimetry performance of natural Brazilian topaz exposed to beta radiation

Optically stimulated luminescence (OSL) has become the technique of choice in many areas of dosimetry. Natural materials like topaz are available in large quantities in Brazil and other countries. They have been studied to investigate the possibility of use its thermoluminescence (TL) properties for dosimetric applications. In this work, we investigate the possibility of utilising the OSL properties of natural Brazilian topaz in dosimetry. Bulk topaz samples were exposed to doses up to 100 Gy of beta radiation and the integrated OSL as a function of the dose showed linear behaviour. The fading occurs in the first 20 min after irradiation but it is <6% of the integrated OSL measured shortly after exposure. We conclude that natural colourless topaz is a very suitable phosphor for OSL dosimetry.     

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.     

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.     

A real-time,fibre optic dosimetry system using Al2O3 fibres

Al2O3:C optical fibres were examined for potential use as real-time luminescence dosemeters for use in radiotherapy applications. The dosimetric properties of the fibres were studied in order to determine their usefulness as luminescence dosemeters. The measurements were performed by connecting the Al2O3:C fibres to a standard fused silica optical fibre and the optically stimulated luminescence (OSL) and radioluminescence (RL) were measured through the fibre. The OSL and RL responses of the Al2O3 fibre probes were measured during irradiation to determine the potential of the Al2O3:C fibres in a real-time fibre optic dosimetry system.     

Ionisation density dependence of the optically and thermally stimulated luminescence from Al2O3:C

This paper presents an overview of recent results on ionisation density dependence of the thermally stimulated luminescence (TL) and optically stimulated luminescence (OSL) signals from Al2O3:C, with emphasis on the sensitivity, efficiency, shape of the TL/OSL curves and the emission spectrum. High-ionisation densities are created uniformly by accumulated high doses of low-linear energy transfer radiation (gamma, beta, X rays) or non-uniformly in heavy charged particle tracks, even at low fluences, as in the case of space radiation fields. Significant deep trap filling, which occurs at these high-ionisation densities, ultimately results in changes in the concentration of recombination centres (F+-centres) and, consequently, in sensitivity changes and other effects. An OSL emission band at 335 nm has been observed in addition to the main F-centre luminescence band, and the relative intensities of these bands have been observed to be dependent on the ionisation density. The implications of these results and open issues are discussed.     

Design of a finger ring extremity dosemeter based on OSL readout of alpha-Al2O3:C

A finger-ring dosemeter and reader has been designed that uses OSL readout of alpha-Al2O3:C (aluminium oxide). The use of aluminium oxide is important because it allows the sensitive element of the dosemeter to be a very thin layer that reduces the beta and gamma energy dependence to acceptable levels without compromising the required sensitivity for dose measurement. OSL readout allows the ring dosemeter to be interrogated with minimal disassembly. The ring dosemeter consists of three components: aluminium oxide powder for measurement of dose, an aluminium substrate that gives structure to the ring, and an aluminised Mylar cover to prevent the aluminium oxide from exposure to light. The thicknesses of the three components have been optimised for beta response using the Monte Carlo computer code FLUKA. A reader was also designed and developed that allows the dosemeter to be read after removing the Mylar. Future efforts are discussed.     

Blue light stimulated luminescence in calcium fluoride, its characteristics and implications in radiation dosimetry

Strong optically stimulated luminescence (OSL), stimulated by blue light, has been observed, for the first time, in natural calcium fluoride (CaF(2)) phosphor, used as thermoluminescence dosemeters. Traps responsible for all three thermoluminescence (TL) peaks appearing upto 300 degrees C, i.e. 126, 196 and 264 degrees C, were observed to contribute to the blue light stimulated luminescence (BLSL) in CaF(2). When the areas under the respective curves (BLSL and TL) were measured, the BLSL measured at room temperature was found to be approximately 1.8 times the TL output of the dosimetry peak that appeared at approximately 264 degrees C. However, when measured after thermally annealing the first two TL peaks, the BLSL signal was found to be 0.26 times the TL output of the dosimetry peak at 264 degrees C. This paper describes the characteristics of the BLSL signal using linearly modulated OSL after subjecting the phosphor to different annealing treatments. Feasibility studies to assess the usefulness of BLSL in CaF(2) for environmental radiation monitoring are also discussed.     

Angular dependence of the TL reading of thin alpha-Al2O3:C dosemeters exposed to different beta spectra

The angular dependence of the thermoluminescent (TL) signal of thin alpha-Al2O3:C dosemeters was investigated for a series of beta-emitting radionuclides commonly employed in nuclear medicine and characterised by different mean energies (99Tc, 177Lu, 90Sr/90Y and 90Y). Irradiations were performed in a controlled geometry, using a properly designed irradiator intended to realistically reproduce the situation of exposure of hospital personnel to beta-emitting pharmaceuticals. Under the conditions of extended source and short source to detector distance, the TL signal of thin alpha-Al2O3:C layers per unit irradiation time was observed to be independent on the angle of incidence within acceptable limits, particularly for those radionuclides with maximum energy >500 keV. This property may be easily explained by using simple physical considerations, such as the limited thickness of the dosemeters. The results confirm that these detectors are suitable for beta-ray extremity dose measurements, when the photon contribution is negligible, as in the case considered.     

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.     

A comparison of quartz OSL and isothermal TL measurements on Chinese loess

The reliability of equivalent doses (De) from Chinese loess, measured using isothermal thermoluminescence (ITL) is tested. Dose calculations use the single-aliquot regenerative-dose (SAR) procedure. Despite good reproducibility of laboratory-induced signals and negligible response at zero dose, a significant overestimation of De is observed, compared with OSL measurements. Measurement of a known laboratory dose administered after optical bleaching, but before any heating, demonstrates that the first heating during measurement of the natural signal causes a significant sensitivity change, undetected by SAR. Using the single-aliquot regeneration and added (SARA) dose procedure, which allows for initial sensitivity change, good agreement with OSL is obtained after allowance is made for initial incomplete bleaching. It is concluded that SAR-ITL, in its present form, is not a suitable method for dating Chinese loess; it is very important to undertake a dose recovery test before any TL procedure is used to date sediments.     

Development of the IFJ single ion hit facility for cell irradiation

In recent years, a single ion hit facility has been constructed at the IFJ ion microprobe. The setup is used for the precise irradiations of living cells by a controlled number of ions. Investigations of such type have two very important requirements: (1) cells must be examined in their natural state and environment (i.e. without previously being killed, preferentially neither fixed nor stained) and (2) the possibility of automatic irradiation of large number of cells (including computer recognition of cells positions) must be provided. This work presents some of the crucial features of the off-line and on-line optical systems, including self-developed software responsible for automatic cell recognition.     

Electron spin resonance evaluation of pure CaSO4 and as a phosphor doped with P and Dy

Polycrystalline CaSO4 powder, doped with different elements but mainly rare earths, is one of the most interesting thermoluminescent (TL) materials. Although many electron spin resonance (ESR) analyses have been reported for these materials few studies have been published about the potential of CaSO4 for ESR dosimetry; almost all studies used CaSO4:Dy with a very low Dy concentration as the material for TL measurements. Pure CaSO4 from Merck was used to prepare CaSO4:Dy and CaSO4:P:Dy with different Dy concentrations. Samples were annealed at 600 degrees C for 1 h before irradiation in a Gammacell 220 irradiator with a 60Co gamma source at a dose rate of 100 Gy x min(-1). The ESR spectra of the pure CaSO4 and CaSO4 doped with P and Dy show the lines usually observed with these types of material, with the factor g around 2.036 and an intense line at g = 2.0011 found only in the pure material. This line, probably an axial SO4-, grows linearly with absorbed dose until 1.0 kGy and shows good stability with time. The line should be stabilized by matrix impurities because it can be removed by a simple treatment with hot sulphuric acid.     

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.     

A thermoluminescence study on the state of Cl in ZnS:Ag by electron beam

The degradation behavior of ZnS:Ag, Cl as a phosphor for CL by EB irradiation at 7 kV was examined by TL measurement. After EB irradiation, TL intensity decreased and the TL peak shifted to the lower temperature side. By comparing TL thermograms of mechanically damaged ZnS:Ag, Cl, ZnS:Cl with varying Cl concentration as well as ZnS:Ag, Al after EB irradiation, we conclude that the decrease in the effective concentration of Cl⁻, serving as active luminescence center, is responsible for the CL degradation of ZnS:Ag, Cl by EB irradiation.     

The PTB microbeam: a versatile instrument for radiobiological research

The PTB microbeam is routinely used for the irradiation of living cells using protons (1-20 MeV) and alpha particles (1-28 MeV). The beam diameter is approximately 2 microm (fwhm), achieved by focussing, resulting in an excellent energy resolution and practically no scattered particles. Recently, an electrostatic beam scanner was added to the facility which allows targeting of each cell within 1 ms. This and other improvements led to an increase in the experimental speed of the system to a maximum of 50,000 cells per hour including all experimental steps. To improve the versatility of the facility further, a module for automatic quantification of immunocytochemical staining was implemented. This allows the analysis of protein activation, taking into account the positional information of the irradiation run.