Commercial optical fibre as TLD material

This work presents a study of commercial SiO2 optical fibre thermoluminescence (TL) properties as part of the efforts within the Dosimetric Application Project at the Physics Institute of the University of Mexico to develop new radiation detection materials and technologies. The SiO2 commercial optical fibre studied demonstrates useful TL properties and is an excellent candidate for use in TL dosimetry of ionising radiation. The optical fibre's glow curve was observed between 30 and 400 degrees C after exposure to 60Co gamma radiation. One very well-defined glow peak has a maximum at 230 degrees C. The TL response between 100 and 350 degrees C increases monotonically over a wide dose range, from 0.1 Gy to several kGy. It is linear in the range 0.1-3 Gy, which is important for clinical high dose or accident dosimetry. The optical fibre demonstrated high data reproducibility, low residual signal and almost no fading in our study. Moreover, the optical fibre can be re-used several times, after thermal annealing, without any detriment in the dose-response. All these TL characteristics, plus the small size of the 150 microm diameter SiO2 optical fibre, the high flexibility, easy handling and low cost compared with other TL materials, make the commercial optical fibre a very promising TL material for use in research, medicine, industry, reactors, and a variety of other applications.     

A system for rapid large-area monitoring of gamma dose rates in the environment based on MCP-N (LiF:Mg,Cu,P) TL detectors

One lesson learned from the Chernobyl accident was that the spatial distribution of far-field contamination was strongly non-uniform due to local variation of atmospheric conditions, such as wind direction, rain etc. An environmental monitoring system using highly sensitive thermoluminescent LiF:Mg,Cu,P (MCP-N) detectors has been completed and field-tested. The system consists of 3000 MCP-N detectors in 1000 TLD cards (three TLDs per card), two Mikrolab automatic TL readers, heating ovens, and specially developed software which includes a database for rapid evaluation of results. The main dosimetric parameters of MCP-N dosemeters, such as thermally-induced fading, light sensitivity, minimum detectable dose, self-dose, zero-dose, energy response up to 6-7 MeV, influence of annealing and readout conditions on detector stability, have been tested. About 100 locations over an area of about 15,000 km2 in the south of Poland were selected for measurements lasting from 4 days to 3 months. The kerma rates measured over a 4 day screening period agree well with kerma rates determined over a 75 day monitoring period. Results from short- and long-term exposure periods agree well with those performed using MTS-N (LiF:Mg,Ti) over southern Poland in 1985, before the Chernobyl accident. Thus, using the system based on MCP-N detectors, one is able simultaneously to monitor environmental radiation kerma rates at a large number of locations over periods of four days or less. Provided natural background kerma rates at selected monitoring points are available prior to the accident, the system can be applied to assess kerma rates rapidly in the environment, following a nuclear accident.     

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.     

Thermoluminescence properties of LiF:Mg,Cu,Na,Si pellets in radiation dosimetry

Sintered LiF:Mg,Cu,Na,Si thermoluminescence (TL) pellets have been developed for application in radiation dosimetry. LiF:M,Cu,Na,Si TL pellets were made from TL powders using a sintering process, that is, pressing and heat treatment. These pellets have a diameter of 4.5 mm, and a thickness of 0.8 mm are blue in colour and have a mass of 28 mg each. After 400 pellets had been produced they were irradiated with 137Cs gamma radiation and samples having a sensitivity within a +/-5% standard deviation were selected for experimental use. In the present study, the physical and dosimetric properties of LiF:Mg,Cu,Na,Si TL pellets were investigated for their emission spectrum, dose response, energy response and fading characteristics. Photon irradiation for the experiments was carried out using X ray beams and a 137Cs gamma source at the Korea Atomic Energy Research Institute (KAERI). The average energies and the dose were in the range of 20-662 keV and 10(-6) - 10(2) Gy respectively. The glow curves were measured with a manual type thermoluminescence dosimetry reader (system 310, Teledyne) at a constant nitrogen flux and a linear heating rate. For a constant heating rate of 5 degrees C.s(-1). the main dosimetric peak of the glow curve appeared at 234 degrees C, its activation energy was 2.34 eV and the frequency factor was 1.00 x 10(23). The TL emission spectrum appeared at the blue region centred at 410 nm. A linearity of photon dose response was maintained up to 100 Gy. The photon energy responses relative to the 137Cs response were within +/-20% in the overall photon energy region. No fading of the TL sensitivity of the pellets stored at room temperature was found over the course of a year. Therefore LiF:Mg,Cu,Na,Si TL pellets can be used for personal dosimetry, but more research is needed to improve the characteristics for repeated use.     

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%.     

Pre- and post-irradiation fading effect for LiF:Mg,Ti and LiF:Mg,Cu,P materials used in routine monitoring

LiF is a well-known thermoluminescent (TL) material used in individual monitoring, and its fading characteristics have been studied for years. In the present study, the fading characteristics (for a period of 150 d) of various commercial LiF materials with different dopants have been evaluated. The materials used in the study are those used in routine procedures by the Personal Dosimetry Department of Greek Atomic Energy Commission and in particular, LiF:Mg,Ti (MTS-N, TL Poland), LiF:Mg,Cu,P (MCP-N, TL Poland), LiF:Mg,Cu,P (MCP-Ns, thin active layer detector, TL Poland) and LiF:Mg,Cu,P (TLD100H, Harshaw). The study showed that there is a sensitivity loss in signal of up to 20 % for the MTS-N material for a 150-d period in the pre-irradiation fading phase. The MCP-N has a stable behaviour in the pre-irradiation fading phase, but this also depends on the readout system. As far as the post-irradiation fading effect is concerned, a decrease of up to 20 % for the MTS-N material is observed for the same time period. On the other hand, the LiF:Mg,Cu,P material presents a stable behaviour within ± 5 %. These results show that the fading effect is different for each material and should be taken into account when estimating doses from dosemeters that are in use for >2 months.     

MCP-N (LiF:Mg,Cu,P) TLDs for radon measurements with charcoal canisters

A method of measurement of radon concentration in air was developed, based on high-sensitivity LiF:Mg,Cu,P (MCP-N, TLD Poland) thermoluminescent detectors installed in charcoal canisters. The canisters were exposed typically for 72 h in a calibration chamber with a radon concentration ranging from 100 Bq x m(-3) to 87 kBq x m(-3). It was found that in these conditions the signal registered by the TL detectors was proportional to the 222Rn concentration and the lowest limit of detection (LLD) was at a level of 100 Bq x m(-3). The proposed method can be used in large-scale, multi-site surveys aimed at screening for high levels of indoor radon concentration or for measuring ground radon exhalation rates.     

Energy response of different types of RADOS personal dosemeters with MTS-N (LiF:Mg,Ti) and MCP-N (LiF:Mg,Cu,P) TL detectors

The photon energy response of different RADOS (Mirion Technologies) personal dosemeters with MTS-N (LiF:Mg,Ti) and MCP-N (LiF:Mg,Cu,P) thermoluminescence (TL) detectors was investigated. Three types of badges were applied. The irradiation with reference photon radiation qualities N (the narrow spectrum series), and S-Cs and S-Co nuclide radiation qualities, specified in ISO 4037 [International Organization for Standardization (ISO). X and gamma reference radiations for calibrating dosemeters and doserate meters and for determining their response as a function of photon energy. ISO 4037. Part 1-4 (1999)], in the energy range of 16-1250 keV, were performed at the Dosimetry Laboratory Seibersdorf. The results demonstrated that a readout of a single MTS-N or MCP-N detector under the Al filter can be used to determine Hp(10) according to requirements of IEC 61066 [International Electrotechnical Commission (IEC). Thermoluminescence dosimetry systems for personal and environmental monitoring. International Standard IEC 61066 (2006)] for TL systems for personal dosimetry. The new RADOS badge with the experimental type of a holder (i.e. Cu/Al filters) is a very good tool for identifying the radiation quality (photon energy).     

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.     

The application of computerised analysis of glow curves to personal dosimetry in LiF:Mg,Cu,P

In personnel monitoring services, it is important to omit the high-temperature annealing process so that large numbers of TL detectors can be produced economically. There are two efficient ways of reducing the residual signal of LiF:Mg,Cu,P. One is by increasing the maximum readout temperature and the other is by improving the preparation procedure (increasing the Cu concentration and the sintering temperature) but both reduce the TL sensitivity. In personal dosimetry the real dosimetric signals are separated from the residual signals by computerised analysis of glow curves. The adverse influence of the high residual signals of LiF:Mg.Cu.P TL material has been effectively eliminated and the sensitivity remains stable. A good dosimetric result using only reader measurement without pre-irradiation oven annealing is attained in a dose range of 50-80,000 microGy.     

Thermoluminescence properties of LiMgF3 doped with Ce,Er and Dy

The main dosimetric properties are reported of a new perovskite, LiMgF3, doped with Ce, Er and Dy impurities. An annealing temperature of 400 degrees C for one hour is necessary to erase any previous signal and to stabilise its sensitivity. A readout up to 450 degrees C gives the same result. The glow curve structure consists of two intense and isolated glow peaks at 170 degrees C and 315 degrees C. The sensitivity of both glow peaks to beta irradiation increases as the dopant concentration increases. The sensitivity is higher than that of LiF:Mg,Ti using the glow peaks 4+5 integral. Other properties like TL dose response, fading, sensitivity versus successive readout and ammealing cycles, sensitivity versus the heating rate, sensitivity to light and trapping parameter evaluation were also carried out.     

Optically and thermally stimulated luminescence characteristics of MgO:Tb3+

In this paper main optically stimulated luminescence (OSL) and thermoluminescence (TL) characteristics are presented of a newly synthesised material MgO doped with terbium (Tb) developed at the Institute of Nuclear Science, Vinca. A thermally stimulated emission spectrum showed the characteristic lines of Tb3+ in a wide range of wavelengths. The TL sensitivity of the main TL glow peak at 315 degrees C is 1.7 times higher than the TL of Al2O3:C. The highest OSL sensitivity was obtained under green lamp (500-570 nm) stimulation. The fast component in the OSL decay curve is 2.4 times faster than Al2O3:C. The OSL signal is linear with dose up to 10 Gy. The lower limit of detection was found to be 100 microGy. These first results show that the newly synthesised material has some promising properties for the application in radiation dosimetry.     

Method of thermoluminescent measurement of radiation doses from micrograys up to a megagray with a single LiF:Mg,Cu,P detector

On the basis of the newly discovered behaviour of LiF:Mg,Cu,P detectors at high and ultra-high doses, a new method of thermoluminescence (TL) measurement of radiation doses ranging from micrograys up to a megagray, has been recently developed at the Institute of Nuclear Physics (IFJ). The method is based on the relationship between the TL signal, integrated in the given temperature range and dose. It is quantified by a parameter called the 'ultra-high temperature ratio'. It has been demonstrated that this new method can measure radiation doses in the range of about 1 μGy to 1 MGy, using a single LiF:Mg,Cu,P detector. This method was recently successfully blindly tested for 10 MeV electrons up to doses of 200 kGy. It can be used for dosimetry in high-energy accelerators, especially in the Large Hadron Collider at CERN, and has great potential for accident dosimetry in particular.     

Nanostructure of pure iron anodically oxidized in borate buffer solution and annealed by infrared radiation

The behavior of oxide film on pure iron passivated in a borate buffer solution and subsequently radiated by infrared light (IR) was investigated in comparing to that by just IR annealing without passivation, and was evaluated by film structure, etc. The effect of thermal annealing over 250 degrees C was observed with gamma-Fe2O3 grain growth and sharp increase in surface roughness, film thickness and oxygen content. An ellipsometric parameter of tan psi was sensitively reflected by annealing effect, and tan psi curve had a shoulder at 150 degrees C for 5 min and a peak of tan psi was shifted from 350 nm to 450 nm in wavelength. This shift was also caused by the formation of gamma-Fe2O3, because the peak was also observed in tan psi of the bulk Fe2O3 family. Passivation effects at 800 mV prior to IR annealing on thickness and oxygen content changed at 150 degrees C, and decreased tan psi at 350 nm and excessive film growth over 250 degrees C, and increased oxygen content under 100 degrees C and surface roughness at 50-250 degrees C. The terrace width with atomic scale flatness was slightly increase by passivation prior to IR annealing at 50-250 degrees C, and the maximum terrace width reached larger than 10 nm by passivation and IR annealing at 100 degrees C for 30 min.     

CVD diamonds as thermoluminescent detectors for medical applications

Diamond is believed to be a promising material for medical dosimetry due to its tissue equivalence, mechanical and radiation hardness, and lack of solubility in water or in disinfecting agents. A number of diamond samples, obtained under different growth conditions at Limburg University, using the chemical vapour deposition (CVD) technique, was tested as thermoluminescence dosemeters. Their TL glow curve, TL response after doses of gamma rays, fading, and so on were studied at dose levels and for radiation modalities typical for radiotherapy. The investigated CVD diamonds displayed sensitivity comparable with that of MTS-N (Li:Mg,Ti) detectors, signal stability (reproducibility after several readouts) below 10% (1 SD) and no fading was found four days after irradiation. A dedicated CVD diamond plate was grown, cut into 20 detector chips (3 x 3 x 0.5 mm) and used for measuring the dose-depth distribution at different depths in a water phantom, for 60Co and six MV X ray radiotherapy beams. Due to the sensitivity of diamond to ambient light, it was difficult to achieve reproducibility comparable with that of standard LiF detectors.     

Thermoluminescence in CVD diamond films: application to actinometric dosimetry

Diamond is considered a tissue-equivalent material since its atomic number (Z =6) is close to the effective atomic number of biological tissue (Z =7.42). Such a situation makes it suitable for radiation detection purposes in medical applications. In the present work the analysis is reported of the thermoluminescence (TL) and dosimetric features of chemically vapour deposited (CVD) diamond film samples subjected to ultraviolet (UV) irradiation in the actinometric region. The TL glow curve shows peaks at 120, 220), 320 and 370 degrees C. The 120 and 370 degrees C peaks are too weak and the first one fades away in a few seconds after exposure. The overall room temperature fading shows a 50% TL decay 30 min after exposure. The 320 degrees C glow peak is considered to be the most adequate for dosimetric applications due to its low fading and linear TL behaviour as a function of UV dose in the 180-260 nm range. The TL excitation spectrum presents a broad band with at least two overlapped components around 205 and 220 nm. The results indicate that the TL behaviour of CVD diamond film can be a good alternative to the currently available dosemeter and detector in the actinometric region as well as in clinical and medical applications.     

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.     

Radiation dosimetry by potassium feldspar

The thermoluminescence (TL) properties of raw and annealed feldspar have been studied for their use in gamma dosimetry. The raw gamma exposed feldspar shows glow peaks at 120°C and 319°C. Gamma dose beyond 500 cGy can be measured without any significant fading even after 40 days of termination of exposure. The annealed feldspar shows a glow peak at 120°C after gamma exposure. This peak can be used to measure gamma doses beyond 25 cGy when the TL is measured after 24 h from termination of exposure.     

Combined TL and 10B-alanine ESR dosimetry for BNCT

The dosimetric technique described in this paper is based on electron spin resonance (ESR) detectors using an alanine-boric compound acid enriched with (10)B, and beryllium oxide thermoluminescent (TL) detectors; with this combined dosimetry, it is possible to discriminate the doses due to thermal neutrons and gamma radiation in a mixed field. Irradiations were carried out inside the thermal column of a TRIGA MARK II water-pool-type research nuclear reactor, also used for Boron Neutron Capture therapy (BNCT) applications, with thermal neutron fluence from 10(9) to 10(14) nth cm(-2). The ESR dosemeters using the alanine-boron compound indicated ESR signals about 30-fold stronger than those using only alanine. Moreover, a negligible correction for the gamma contribution, measured with TL detectors, almost insensitive to thermal neutrons, was necessary. Therefore, a simultaneous analysis of our TL and ESR detectors allows discrimination between thermal neutron and gamma doses, as required in BNCT.     

Preparation,dosimetric characterisation and investigation of related TSL defect centres in Li3Po4:Mg,Cu phosphor

L3PO4:Mg,Cu, a low effective atomic number and high sensitivity TSL phosphor, has been prepared. Its TSL glow curve shows a major peak around 360 degrees C with minor peaks around 110 degrees C and 230 degrees C. The optimum concentrations of the dopants are found to be 200 ppm each. Its gamma sensitivity is 1.2 times as compared to CaSO4:Dy (0.1 mol%). The optimum preirradiation annealing treatment is found to be 650 degrees C, 15 min. Its PL emission shows a band at 370 nm with excitation band at 250 nm. Dose to TSL response shows that its response is linear up to the gamma dose of 100 Gy for irradiations carried out at RT. An irradiated sample shows a distinct new ESR signal, which is tentatively assigned to an electron/hole localised on one of the oxygen(s) of the phosphate group. Step annealing experiments show decay of the defect centre around 340 degrees C. This correlates well with the TSL peak around 360 degrees C.