OSL, RL and TL characterization of rare-earth ion doped K2YF5: Application in dosimetry

Optically stimulated luminescence (OSL) properties of K₂YF₅ crystals singly doped with different concentrations of Tb³⁺ ions and doubly doped with Tb³⁺ and Ce³⁺ or Tb³⁺ and Dy³⁺ have been investigated for the first time. Radioluminescence spectra and OSL efficiency for stimulation with different wavelengths of light have been analyzed for each compound. Also, dosimetric characteristics of the most efficient composition, namely K₂YF₅:1 at.% Tb³⁺, have been studied. Finally, the OSL signal peculiarities for K₂YF₅:1 at.% Tb³⁺ have been compared to those of a commercial Al₂O₃:C dosimeter.     

TL and OSL dosimetric properties of Opal gemstone for gamma radiation dosimetry

In this work, the response of the natural material Opal was studied in relation to its thermoluminescence (TL) and optically stimulated luminescence (OSL), after exposure to the gamma radiation of a ⁶⁰Co source. The structure of the powdered Opal was verified using the X-ray diffraction, scanning electronic microscopy and energy-dispersive X-ray spectroscopy techniques. The material, in its stone form, was turned into powder and mixed to Teflon (also in powder) in three different concentrations, and then pellets were manufactured. The aim of this work was to evaluate the response of these pellets in high-doses of gamma radiation beams, and to observe their possible application as dosimeters, using the TL and OSL techniques. The dosimetric properties of the samples were analyzed by means of different tests, as: TL emission curves and OSL signal decay curves, reproducibility of TL and OSL response, minimum detectable dose, TL and OSL dose–response curves (5 Gy–10 kGy), and fading. The results obtained in this work, for the TL and OSL phenomena, demonstrated that the pellets of Opal + Teflon present an adequate performance e possibility of use as dosimeters in beams of high-dose gamma radiation.     

Light induced fading associated with the application of OSL to personal dosimetry

Al₂O₃:C is the best material example that presents OSL response and adequate dosimetric behaviour for OSL dosimetry. It was the first commercial material manufactured for use in personal monitoring based on an OSL reader system from Landauer. The purpose of this paper was to report the results of optical fading experiments for the nanoDot commercial OSL detectors (Al₂O₃:C), provided by Landauer Inc. Five groups of different experimental conditions were formed with all detectors, exposing them to fluorescent and semiconductor light sources and to sun light. The loss of OSL signal when the detectors are kept open, was verified, which was already expected, but a loss in the OSL signal even when the detectors are exposed to light and covered with the manufacturer plastic protection are also revealed. The results show also that the use of Mylar filters can delay the OSL fading of the detectors.     

Investigation of a fibre-coupled beryllium oxide (BeO) ceramic luminescence dosimetry system

The purpose of this study is to investigate the potential use of a beryllium oxide (BeO) ceramic as a radioluminescence (RL) and optically stimulated luminescence (OSL) probe material for fibre-coupled luminescence dosimetry. A portable dosimetry system, named RL/OSL BeO FOD was developed, consisting of a 1 mm diameter, 1 mm long BeO ceramic cylinder coupled to a silica/silica optical fibre. The reader measures the RL signal and also uses a 450 nm laser diode to stimulate the BeO ceramic. A second background optical fibre is used to remove the stem effect. The RL/OSL BeO FOD was characterised in a solid water phantom, using a 6 MV x-ray beam. The RL was found to be reproducible and have a linear response to doses ranging from 30 cGy–15 Gy and dose rates from 100 cGy/min – 600 cGy/min. The OSL response was linear to doses of 10 Gy, becoming supralinear at higher doses. Measured percentage depth curves using the RL/OSL BeO FOD agreed with those measured using an IC15 ion chamber to within 5%, beyond the build up region. It was also found that the RL from BeO ceramic is unaffected by the delivered dose to the probe and hence, it remains constant for a given dose-rate. The insensitivity of the RL to accumulated dose makes BeO ceramic potentially capable of accurate dose-rate measurements without any corrections for the accumulated dose. This study demonstrates the feasibility of BeO ceramic as a versatile fibre-coupled luminescence dosimeter probe.     

Photon dosimetry methods outside the target volume in radiation therapy: Optically stimulated luminescence (OSL), thermoluminescence (TL) and radiophotoluminescence (RPL) dosimetry

Dosimetry methods outside the target volume are still not well established in radiotherapy. Luminescence detectors due to their small dimensions, very good sensitivity, well known dose and energy response are considered as an interesting approach in verification of doses outside the treated region. The physical processes of thermoluminescence (TL), radiophotoluminescence (RPL) and optically stimulated luminescence (OSL) are very similar and can be described in terms of the energy band model of electron-hole production following irradiation.This work is a review of the main dosimetric characteristics of luminescence detectors which were used in experiments performed by EURADOS Working Group 9 for in-phantom measurements of secondary radiation (scattered and leakage photons). TL LiF:Mg,Ti detectors type MTS-7 (IFJ PAN, Poland), types TLD-100 and TLD-700 (Harshaw), OSL Al₂O₃:C detectors type nanoDot™ (Landauer Inc.) and RPL rod glass elements type GD-352M (Asahi Techno Glass Coorporation) are described. The main characteristics are discussed, together with the readout and calibration procedures which lead to a determination of absorbed dose to water.All dosimeter types used show very good uniformity, batch reproducibility and homogeneity. For improved accuracy, individual sensitivity correction factors should be applied for TL and OSL dosimeters while for RPL dosimeters there is no need for individual sensitivity corrections.The dose response of all dosimeters is linear for a wide range of doses.The energy response of GD-352M type dosimeters (with Sn filter) used for out-of-field measurements is flat for medium and low energy X-rays.The energy dependence for TLDs is low across the range of photon energies used and the energy correction was neglected. A significant over response of Al₂O₃:C OSLDs irradiated in kilovoltage photon beams was taken into account. The energy correction factor f_en was calculated by using the 2006 PENELOPE Monte Carlo code.With suitable calibration, all dosimeter types are appropriate for out-of-field dose measurements as well as for the in-phantom measurements of radiotherapy MV X-rays beams.     

The use of the TL and OSL phenomena for determination of absorbed dose rates of 90Sr + 90Y sources by a postal method

International recommendations establish that ⁹⁰Sr + ⁹⁰Y clinical applicators have to be calibrated in order to determine the absorbed dose rates in the case of the sources that do not have original calibration certificates, or to update the absorbed dose rates presented in the source certificates. Following these recommendations, a postal dosimetric system was developed to calibrate clinical applicators using two luminescent techniques: thermoluminescence (TL) and optically stimulated luminescence (OSL). In this work, Al₂O₃:C commercial detectors were characterized and their TL and OSL responses were analyzed. The results showed the efficiency and the optimal behavior of this material in beta radiation beams. After characterization, the system was sent to the Federal University of Sergipe (UFS), Brazil, for calibration of five ⁹⁰Sr + ⁹⁰Y clinical applicators, where the detectors were irradiated and returned to IPEN, for their evaluation and determination of the absorbed dose rates. A comparison between these absorbed dose rates and those adopted by the UFS as original was made; the differences obtained were within those of other studies, and they demonstrated the usefulness of the system.     

White light-emitting diodes for optical stimulation of aluminium oxide in OSL dosimetry

The results of comparative investigations into the optically stimulated luminescence (OSL) of anion-defective corundum excited by radiation of blue and white light-emitting diodes (LEDs) are reported. The continuous-wave OSL (CW-OSL) measurements showed that the white LED (compared to the blue LED) and the chosen geometry allow the amplitude of the OSL response to increase by a factor of more than 40 and the dosimetric information readout time to decrease by a factor of 20.The effect of deep traps on the behavior of the CW-OSL curves of anion-defective corundum was studied. It was found that the filling of deep traps essentially increases the TL yield with a dosimetric peak at 450 K and the CW-OSL-yield under stimulation with blue and white LEDs. It was also found that this filling causes a considerable change in the shape of the OSL curve and the time parameters of the decay.     

Time-resolved OSL studies of YAlO3:Mn2+ crystals

Time-Resolved Optically Stimulated Luminescence (TR-OSL) from single crystalline YAlO₃:Mn²⁺ samples was investigated using a green light emitting diode (λ ∼ 525 nm) as stimulation light source. The TR-OSL decay curve of the material can be described with a single exponential decay function with a lifetime about 80 ms that does not depend on irradiation dose in the range from 50 mGy to 1 kGy. This OSL decay is superposed on a photoluminescence signal with a much shorter (3.5 ms) decay lifetime. The Mn²⁺ photoluminescence decay with a lifetime of 3.5 ms can be easily eliminated by corresponding time resolution using pulsed OSL readout. Dose response and thermal stability of the OSL signal are consistent with the previous thermoluminescent (TL) studies of the material.     

Real time dose rate measurements with fiber optic probes based on the RL and OSL of beryllium oxide

This work covers the examination of fiber optical probes based on the radioluminescence and real time optically stimulated luminescence of beryllium oxide. Experiments are carried out to determine the fundamental dosimetric and temporal properties of the system and evaluate its suitability for dose rate measurements in brachytherapy and other applications using non-pulsed radiation fields. For this purpose the responses of the radioluminescence and optically stimulated luminescence signal have been investigated in the dose rate range of 20 mGy/h to 3.6 Gy/h and for doses of 1 mGy up to 6 Gy. Furthermore, a new, efficient analysis procedure, the double phase reference summing, is introduced, leading to a real time optically stimulated luminescence signal. This method allows a complete compensation of the stem effect during the measurement. In contrast to previous works, the stimulation of the 1 mm cylindrical beryllium oxide detectors is performed with a symmetric function during irradiation. The investigated dose rates range from 0.3 to 3.6 Gy/h. The real time optically stimulated luminescence signal of beryllium oxide shows a dependency on both the dose rate and the applied dose. To overcome the problem of dose dependency, further experiments using higher stimulation intensities have to follow.     

The dependence of quartz OSL on stimulation energy

Quartz is the mineral most commonly used for sediment dating. In dating practice, the optically stimulated luminescence (OSL) of quartz is measured mainly using the stimulation light whose wavelength is 470 ± 30 nm. The parameters of traps active in the OSL process are also determined for this stimulation band. The zeroing of the OSL is the fundamental condition of applicability of the luminescence dating for specific sediment and takes place in sunlight whose spectrum differs significantly from the band 470 ± 30 nm. In order to be able to know the course of OSL process in nature, a wider knowledge of the dependency of the trap parameters on the stimulation band is needed. Here the results are presented for the OSL measurements carried out with different wavelengths of stimulation light. For each stimulation band the components of the OSL signal are determined by the fitting procedure, and in this way the wavelength dependence of an individual component is found. The experiment has been repeated for two temperatures of OSL detection – the room temperature, which corresponds to natural conditions, and for 125 °C, which is the temperature usually applied for OSL measurement in dating. Four OSL components are presented in both experimental series. The values of their optical cross-section changes along with stimulation energy and temperature, as it is predicted by the model of OSL process including crystal lattice vibrations.     

Analysis of TL and OSL kinetics of lithium aluminate

Lithium aluminate (LiAlO₂) polycrystalline material showing high OSL sensitivity and linear dose response was prepared at IFJ Krakow. The kinetic parameters of OSL and TL processes were evaluated using various experimental techniques: LM-OSL deconvolution, TL glow-curve deconvolution, variable heating rate and isothermal decay. The OSL signal was found to consist of four components, one of them exhibiting a very slow decay. The TL glow-curve possesses two apparent peaks at approximately 85 °C and at 165 °C, which both seem to follow first order kinetics. These peaks seem to have a composite structure and as many as six peaks were found in the glow-curve.     

OSL dosimetric properties of cerium doped lutetium orthosilicates

This paper presents selected optically stimulated luminescence properties of Lu₂SiO₅:Ce single crystalline films grown using Liquid Phase Epitaxy technique. Comparison of continuous wave optically stimulated luminescence decay curves under blue and green light stimulation is shown. The dose response characteristic is found to be linear in the studied range from 100 μGy to 1 Gy. Analyses of the linearly modulated optically stimulated luminescence signal enabled establishing of the photoionization cross sections for blue light (470 nm). Bleachability and thermal stability of CW–OSL signal are discussed, as well as preliminary results of the fading study.     

A new modular high capacity OSL reader system

A new modular OSL system built on a 60-sample automation platform is described, upon which are installed a compatible family of sample elevator/heater mechanisms, OSL exciters, photon counting detectors, and irradiators. All components may be changed out, including the control electronics, firmware, and status display. The excitation family includes modules for both large area and arrays of single grains. The detector family has both single and quad (multispectral) capabilities. Both irradiation and detection stations are temperature controlled.     

Influence of pre-measurement thermal treatment on OSL of synthetic quartz measured at room temperature

Much effort has been made to study the influence of pre-measurement thermal treatment and ionizing radiation on quartz specimens owing to its use in a large number of applications. Optically stimulated luminescence (OSL) being a structured and sensitive phenomenon promises to correlate the responsible color center and luminescence emission. OSL studies on quartz with such conditions can reveal many significant results.The aim of the present investigation is to understand the effect of annealing temperature on OSL characteristics of synthetic quartz recorded at room temperature. At identical annealing duration and β-dose, the shape of OSL decay curve remains non-exponential; when specimens annealed at lower temperature (∼400 °C). The shape of decay curve changes to exponential in nature along with rise in OSL intensity when the specimen was given higher temperature of annealing (>400 °C). The effects of such protocol on pattern of OSL sensitivity as well as area under the OSL decay curve are also presented here. The presence of shallow traps, when OSL decay curve was recorded at room temperature seems to be responsible for the changes in OSL pattern. The influence of shallow traps is attributed to non-exponential decay of OSL recorded at room temperature.     

Investigations of OSL properties of LiMgPO4:Tb,B based dosimeters

Lithium magnesium phosphate LiMgPO₄ (LMP) doped with Tb and B is one of new materials intended for use in optically stimulated luminescence (OSL) dosimetry. LMP doped with Tb and B luminophors were synthetized at IFJ PAN in Krakow. The investigations were carried out on self-developed dosimeters consisting of a slide with four LMP detectors and a light tight cover. LMP detectors were investigated in regard to their OSL properties using OSL reader named HELIOS adopted to the readouts of dosimetric cards. New LMP detectors showed high sensitivity to the ionizing radiation, good repeatability of OSL signal and good dose response, 25% of fading in the first two weeks after irradiation. Also, the pronounced dependence of OSL response on the energy of the measured radiation requires to apply the compensation filters.     

Emergency OSL dosimetry with commonplace materials

Several commonplace materials were studied as possible emergency optically stimulated luminescence (OSL) dosimeters. The materials included: paper currency (banknotes) and coins of different denomination and from different countries; plastic cards of different types (credit and debit cards, driver's license cards, membership cards, etc.), parts and details of clothing and shoes as well as samples of different fabrics.The samples displayed significant variability in their OSL properties. They differed in the intensity of the initial ‘native’ signal; the bleaching time of the OSL signal; the sensitivity to light of different wavelengths; the fading rate of OSL signals, etc. Procedures of OSL analysis were proposed to account for this variety.Values of the minimum measurable dose (MMD) were below 2 Gy for most tested samples if OSL measurements were conducted within one week of exposure and the samples were kept in dark since exposure (except samples of shoes that were kept under environmental light).The OSL signals in banknotes appear to originate from compounds containing aluminum, silicon, calcium and titanium – these elements were detected using X-ray microanalysis. For coins, the source of the OSL signals is speculated to be small particles of quartz, which were detected on the coins' surfaces. The X-ray microanalysis spectra from fabrics and shoes revealed sodium, aluminum, titanium, iron and nickel as elements that appeared to be responsible for the radiation sensitivity of those samples.It was concluded that, under certain constrained circumstances, paper and metallic money, personal plastic cards, clothing and shoes could be used as emergency OSL dosimeters in triage applications.     

Optically stimulated luminescence in Ag doped Li2B4O7 single crystal and its sensitivity to neutron detection and dosimetry in OSL mode

Optically stimulated luminescence (OSL) measurements have been carried out on single crystals of Ag doped Li₂B₄O₇ (LTB:Ag) after exposure to various nuclear radiations. The time integrated OSL intensity is found to be linear in the range from 0.1 Gy to 500 Gy. Fading of the OSL signal was found to be around 36% in 48 h. The presence of ⁶Li and ¹⁰B has been gainfully utilized to measure doses of thermal neutrons. Further, the large difference between the wavelength of the stimulation source (∼460 nm) and emission from the LTB:Ag at 270 nm has enhanced the signal-to-noise ratio in a simple OSL set-up with suitable filters. The high sensitivity of the LTB:Ag to thermal neutrons will be useful in variety of applications including personal dosimetry in mixed-fields and imaging devices for neutron radiography.     

Characterisation of a real-time fibre-coupled beryllium oxide (BeO) luminescence dosimeter in X-ray beams

For the first time the feasibility of using beryllium oxide (BeO) ceramics as a fibre-coupled radioluminescent dosimeter is investigated. BeO ceramic exhibits both radioluminescence (RL) and optically stimulated luminescence (OSL), and has the potential to be a near tissue equivalent alternative to Al₂O₃:C. A BeO fibre-coupled radioluminescence dosimeter is demonstrated and characterised for 6 MV X-rays and superficial X-ray energies, 150 kVp and 120 kVp. Based on the results, we demonstrate the capability of the RL BeO FOD for accurate and reproducible dose measurements with a linear dose rate and dose response. It has also been found that the percentage depth dose curves for 6 MV agreed with ion chamber measurements to within 2%, except in the build up region. For the 150 kVp and 120 kVp photon beams, the depth dose measurements agreed with ion chamber measurements to within 2.5% and 4%, respectively.     

Influence of thermal treatment on OSL regeneration in potassium chloride

Optically stimulated luminescence (OSL) of pure analytical potassium chloride (KCl) prepared in two different forms (crystals and pellets) was studied. The occurrence of regeneration effect (self-renewal of the OSL signal) in the material was examined. The experiments using the variable delay OSL (VD-OSL) method were carried out. Performed measurements allowed to determine time scale of the phenomenon, as well as quantitative changes of regeneration depending on thermal treatment before and after irradiation. Significant increase of the OSL regeneration was noticeable for pellets after the application of the annealing before irradiation, while for crystals a substantial decrease of regeneration was observed. Preheating applied after irradiation caused that self-renewal of OSL signal was drastically reduced or completely suppressed depending on the form of KCl samples.