Luminescence properties of biotite relevant to dating and dosimetry

Biotite mineral grains from granitic rocks were subjected to luminescence studies with optical and thermal stimulation. Moderate thermoluminescence (TL) signals and weak optically stimulated luminescence (OSL) with blue-green light stimulation were detected after 50 Gy beta irradiation. No detectable infrared-stimulated luminescence (IRSL) was observed for natural and laboratory beta-irradiated samples. TL peaks at 118, 300, 360 and 480 °C can be identified from laboratory-irradiated samples. The 360 °C TL peak saturates at a higher dose than quartz, but shows significant anomalous fading after 80 days stored at room temperature. The potentials and problems for biotite used as a natural dosimeter are discussed.     

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.     

Study of TSL and OSL properties of dental ceramics for accidental dosimetry applications

Interest is increasing in the development of new methodologies for accidental dose assessment, exploiting the luminescence and dosimetric properties of objects and materials which can be usually found directly on exposed subjects and/or in the contaminated area.In this work, several types of ceramics employed for dental prosthetics restoration, including both innovative materials used as sub-frames for the construction of the inner part of dental crowns (core), and conventional porcelains used for the fabrication of the external layer (veneer), were investigated with regard to their thermally and optically stimulated luminescence (TSL and OSL respectively) properties, in view of their potential application in accidental dosimetry.The sensitivity to ionizing radiation proved to strongly depend on the type and brand of ceramic, with minimum detectable dose ranging from few mGy up to several tens of mGy. A linear dose–response was observed for most of the samples. However, the luminescence signals were characterised by a significant fading, which has to be taken into account for a reliable accidental dose assessment after a radiation exposure event.     

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.     

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.     

Luminescence from NaCl for application to retrospective dosimetry

The alkali halide NaCl (Common salt) is an environmentally-abundant phosphor of considerable potential for retrospective dosimetry and radiological event analysis due to its high sensitivity to ionising radiation when analysed by Thermoluminescence (TL), Optically-stimulated luminescence (OSL) or Infrared-stimulated luminescence (IRSL). We report here aspects of luminescence from NaCl relevant to the development of valid protocols for measurement of recent ionising radiation exposure. The timescale of interest in this application is from days to decades, hence our emphasis is on detection and characterisation of TL emission in the 100–300 °C range, and of OSL and IRSL emissions measured following only low temperature preheating (160 °C). A collection of 19 salt samples was assembled, including samples of rock salt and domestic salt produced by evaporation from brine. Analysis of TL emission spectral changes, together with previously reported TL, OSL and IRSL sensitivity changes, confirmed activation of sensitivity change by exposure to temperatures exceeding 160 °C. Kinetic analysis using Chen's method found E = 0.943 eV and s = 5.1 × 10¹¹ s^?1 for the 100 °C TL peak, giving a lifetime at 20 °C consistent with previous calculations and in the range of 7–14 h.     

Medical dosimetry using a RL/OSL prototype

A portable and robust instrument has been developed for the routine assessment of patient exposure to ionizing radiation during radiotherapy treatments. The design principles of hardware and software are described, along with preliminary measurements that illustrate the operation of the system and its capabilities. In this study the authors used radioluminescence (RL) and Optically Stimulated Luminescence (OSL) from Al₂O₃:C detectors coupled to a PMMA optical fibre to acquire dose in medical dosimetry. The RL/OSL prototype can provide two independent dose estimates from the same in vivo treatment: one integrated dose estimate (OSL) and one real-time dose estimate (RL), which can be compared to one another. The authors first characterized the dose–response to a calibration source (¹³⁷Cs), analysing the OSL and the RL signal to doses from 0.5 to 3 Gy. Later the percentage dose depth from RL is presented for two gamma (6 and 15 MV) and two electron (6 and 12 MeV) medical beams.     

Crushing effects on TL and OSL on quartz: relevance to fault dating

The effect of crushing on the TL and OSL signals in quartz was investigated to examine the feasibility of using OSL and TL for dating of faulted rocks. 275°C TL signals were not reduced by crushing by hand (mortar and pestle), in a pellet die press, or using an automatic mortar and pestle, but the sensitivity of the 100°C TL signal to a test dose decreased in crushed samples. Green light-stimulated OSL signal intensities were not decreased after crushing, but showed strongly increased inter-aliquot variability after crushing. We concluded that OSL and TL in quartz might be useful to characterize the crushing history of quartz in fault rocks, but their usefulness in dating fault events was not evident because we did not find evidence of signal zeroing under the conditions used in this study.     

Quartz OSL: Effects of thermal treatment and their relevance to laboratory dating procedures

In dating procedures, whether single or multiple aliquot, OSL signals are obtained after samples have been heated in the laboratory with preheat procedures as short as a few seconds or as long as several hours. The OSL signals may be obtained whilst stimulating at a variety of temperatures. These thermal treatments will affect both the trapped electron population(s) in the material and the recombination centres (or trapped hole populations). Several effects may occur simultaneously. Experimental evidence is presented which is used to select the most appropriate thermal treatments in laboratory dating procedures.     

IRSL characteristics of NaCl and KCl relative to dosimeter

The aim of this work is to determine and compare the dosimetric properties of NaCl and KCl samples using infrared-stimulated luminescence (IRSL) technique. For a material to be used as dosimeter, both the IRSL temperature dependence and the radiation dose response have critical importance. In this work the IRSL characteristics from NaCl and KCl samples were experimentally investigated as a function of temperature and laboratory radiation doses. Dosimetric properties of NaCl and KCl samples were found significantly different. The IRSL signals displayed by NaCl were found to be more stable, reliable and agreeable than those of KCl.     

A spectral radioluminescence study for dating and dosimetry

The spectral distribution of radioluminescence (RL) and its dose dependence was investigated on various substances to get information about the applicability in dosimetry and dating. The list comprises archaeometallurgical slag components (quartz relicts, glassy fraction), bone, cooking salt, corals, egg shell, flint, mussel shell, natural gypsum, natural halite, quartz (sediments, vein quartz) and sugar. The different emission wave-bands and basic features of their RL-dose-characteristics are reported for 18 different samples. Furthermore results of some materials are discussed in more detail.     

The effects of low ambient temperatures on optically stimulated luminescence (OSL) processes: Relevance to OSL dating of martian sediments

Advances in luminescence dosimetry have made geochronological dating of materials from extreme environments possible through the use of optically stimulated luminescence (OSL) single-aliquot techniques. However, these environments present challenges not always encountered in routine OSL dating, such as sediments that have been stored at low, and possibly highly variable, ambient temperatures. In recent years OSL has been proposed as a method for dating recent depositional events on surfaces of other planets, specifically, Mars. As a result it has become necessary to examine the constraints that may be imposed on the OSL method by the extreme environments of extraterrestrial planetary bodies. In this paper we report on investigations of the possible effects a low storage and/or a low OSL measurement temperature could have on the OSL process and the subsequent results. Pertinent OSL properties include the stability of electron traps, the overall luminescence efficiency, and possible thermal assistance processes. The particular focus of the work is on the potential application of the OSL technique for dating surface sediments on Mars. We report the results of OSL experiments on martian simulant materials, and of generalized computer simulations of potential OSL behavior. It is concluded that the stimulation and irradiation/calibration temperatures need to be maintained fixed throughout the experiment – i.e. the dose estimation process – and that the temperature during OSL stimulation needs to be appreciably higher than the highest temperature experienced during natural irradiation. The consequences of these findings for establishing an OSL protocol and instrument package for dating martian regolith material are discussed.     

OSL and TL in TLD-100 following alpha and beta 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 measurement of the excitation and emission spectra of OSL and comparison with thermoluminescence (TL) characteristics. The OSL excitation spectra of all the samples following both beta and alpha irradiation are very similar.Identical emission bands with very similar relative intensities following both beta irradiation and alpha particle irradiation have been recorded in the OSL induced in nominally pure LiF mono and TLD-100 polycrystals. The identical excitation and emission bands in the doped and pure crystals are strong evidence indicating that the observed OSL is due to an intrinsic trapping structure. The OSL has indeed been previously attributed to F₂ centers and F₃⁺ centers.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⁺ center, 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 (LID) radiation and may have significant potential in mixed-field radiation dosimetry.     

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.     

OSL and TL retrospective dosimetry with a fluorapatite glass-ceramic used for dental restorations

Optically Stimulated Luminescence (OSL) and Thermoluminescence (TL) properties of a fluorapatite glass-ceramic have been investigated, with a view to developing a dose assessment technique for medical triage following unplanned exposures of individuals to ionizing radiation. The ceramic is an innovative material used in dental prostheses and restorations. It is strongly sensitive to radiation and the intensity of both the OSL and TL signals are proportional to the absorbed radiation dose. We focused on the optimization of the measuring procedure and investigated characteristics such as reproducibility, fading, minimum detectable dose (MDD), dose response and photon energy response of TL and OSL signals. The dental ceramic exhibited very good reproducibility (<5% at 2σ level) when measured and a linear dose response for a wide range of doses (50 mGy–20 Gy). The MDD values for the samples investigated were ∼5 mGy. The material is not tissue equivalent and the OSL and TL signals are strongly dependent on incident photon energy. Both the luminescence signals exhibited significant fading during the first few hours after irradiation. Its rate was dependent on the parameters of measurement. The results indicate that the material can be used for the purposes of accident dosimetry, however, the fading and photon energy response have to be properly corrected for a reliable dose assessment.     

Synthesis and luminescence in some fluoro-silicates for the possible applications in OSL dosimetry

Various fluoro-silicates, viz. M₂SiF₆ (M=Li, Na, K) were synthesized by reacting the mixture of corresponding salt and silicic acid with Hydrofluoric acid. The thermal analysis of these materials was performed. These materials were doped with ions Ce³⁺, Cu⁺, Ag⁺ and photoluminescence, TL, OSL properties were studied. Intense TL and OSL was observed from these materials. Due to decomposition during heating, these materials may not be suitable as TL Phosphors, but will be good phosphors for radiation dosimetry using OSL.     

Application of the optically stimulated luminescence (OSL) technique in space dosimetry

This paper reviews the state of the optically stimulated luminescence (OSL) technique for space dosimetry applications, focusing on the properties of carbon-doped aluminum oxide (Al₂O₃:C). New data presented include the most complete and recent values for the relative efficiency η_HCP,γ for heavy charged particles as a function of the incident radiation's linear energy transfer (LET), obtained through ground-based experiments at heavy ion accelerators. We also discuss the factors influencing the OSL efficiencies, the LET-dependent properties of Al₂O₃:C, and the experience gained from past space experiments using Al₂O₃:C. The characterization of the OSL efficiency values as a function of LET allows the use of the OSL of Al₂O₃:C in combination with plastic nuclear track detectors for personal dosimetry of astronauts, as proposed by the NCRP Report 142.