An investigation of the thermoluminescence of Ge-doped SiO2 optical fibres for application in interface radiation dosimetry

We investigate the ability of high spatial resolution (～120 μm) Ge-doped SiO2 TL dosimeters to measure photoelectron dose enhancement resulting from the use of a moderate to high-Z target (an iodinated contrast media) irradiated by 90 kVp X-rays. We imagine its application in a novel radiation synovectomy technique, modelled by a phantom containing a reservoir of I2 molecules at the interface of which the doped silica dosimeters are located. Measurements outside of the iodine photoelectron range are provided for using a stepped-design that allows insertion of the fibres within the phantom. Monte Carlo simulation (MCNPX) is used for verification. At the phantom medium I2-interface additional photoelectron generation is observed, ～60% above that in the absence of the I2, simulations providing agreement to within 3%. Percentage depth doses measured away from the iodine contrast medium reservoir are bounded by published PDDs at 80 kVp and 100 kVp.     

Establishment of Ge-doped optical fibres as thermoluminescence dosimeters for brachytherapy

This study aims to establish the sensitive, ～120 μm high spatial resolution, high dynamic range Ge-doped optical fibres as thermoluminescence (TL) dosimeters for brachytherapy dose distribution. This requires investigation to accommodate sensitivity of detection, both for the possibility of short range dose deposition from beta components as well as gamma/x-mediated dose. In-air measurements are made at distances close to radionuclide sources, evaluating the fall off in dose along the transverse axis of 133Ba and 60Co radioactive sources, at distances from 2 mm up to 20 mm from their midpoints. Measurements have been compared with Monte Carlo code DOSRZnrc simulations for photon-mediated dose only, agreement being obtained to within 3% and 1% for the 133Ba and 60Co sources, respectively. As such, in both cases it is determined that as intended, beta dose has been filtered out by source encapsulation.     

The thermoluminescence response of doped SiO2 optical fibres subjected to fast neutrons

This paper describes a preliminary study of the thermoluminescence (TL) response of doped SiO₂ optical fibres subjected to ²⁴¹AmBe neutron irradiation. The TL materials, which comprise Al- and Ge-doped silica fibres, were exposed in close contact with the ²⁴¹AmBe source to obtain fast neutron interactions through use of measurements obtained with and without a Cd filter (the filter being made to entirely enclose the fibres). The neutron irradiations were performed for exposure times of 1-, 2-, 3-, 5- and 7-days in a neutron tank filled with water. In this study, use was also made of the Monte Carlo N-particle (MCNP^TM) code version 5 (V5) to simulate the neutron irradiations experiment. It was found that the commercially available Ge-doped and Al-doped optical fibres show a linear dose response subjected to fast neutrons from ²⁴¹AmBe source up to seven days of irradiations. The simulation performed using MCNP5 also exhibits a similar pattern, albeit differing in sensitivity. The TL response of Ge-doped fibre is markedly greater than that of the Al-doped fibre, the total absorption cross section for Ge in both the fast and thermal neutrons region being some ten times greater than that of Al.     

Thermoluminescent dosimeters for exposure assessment in gamma or x radiation fields with unknown spectral distribution

The determination of the effective energy of a radiation field using the energy dependence of the response ratio of two dosimeters with different energy dependences is called the “Tandem Method”. Having in view the choice of the best pair of dosimeters to be used, the energy response characteristics of LiF: Mg, Ti; CaSO₄: Dy; CaF₂: Dy and CaF₂: Mn thermoluminescent (TL) dosimeters were studied. Two different physical forms of TL dosimeters were investigated: hot pressed chips and Teflon disc dosimeters. The calibration factors were obtained for the energy of ⁶⁰Co γ rays and their energy dependence, normalized to ⁶⁰Co γ-radiation, was determined using spectral width as a parameter. Tandem systems formed by all TL dosimeters evaluated were compared. It was concuded that the Tandem DCaSO₄: Dy−0.4/ LiF: Mg, Ti (TLD-100) determines the effective energy with a maximum uncertainty of only 10 keV and permits the assessment of the energy correction factor for the TLD-100 with a precision of better than 1.7% for the spectral distribution studied in the effective energy range from 30 to 100 keV.     

Evaluation of doses in radiotherapy using solid-state composites based on natural colourless topaz.

The thermoluminescent properties of composites containing powdered topaz embedded in Teflon or glass were studied and compared with the corresponding properties of the well known TLD-100 commercial dosimeters. Relative sensitivity, TL fading, reproducibility of the sample preparation process, and possibility of re-utilisation of the dosimeters were investigated. Measurements of absorbed doses in simulated radiotherapy treatments were also taken. The irradiations were performed using gamma rays from a 60Co source in the dose range from 1cGy to 2Gy. The dosimeters were installed in badges and attached inside acrylic plates of various thicknesses in the radiation fields. The dose profiles obtained with this procedure are very similar to the ones obtained with equivalent tissues. It is concluded that these composites of natural colourless topaz crystals can be efficiently used as TL dosimeters.     

The thermoluminescence response of doped SiO2 optical fibres subjected to photon and electron irradiations

Modern linear accelerators, the predominant teletherapy machine in major radiotherapy centres worldwide, provide multiple electron and photon beam energies. To obtain reasonable treatment times, intense electron beam currents are achievable. In association with this capability, there is considerable demand to validate patient dose using systems of dosimetry offering characteristics that include good spatial resolution, high precision and accuracy. Present interest is in the thermoluminescence response and dosimetric utility of commercially available doped optical fibres. The important parameter for obtaining the highest TL yield during this study is to know the dopant concentration of the SiO₂ fibre because during the production of the optical fibres, the dopants tend to diffuse. To achieve this aim, proton-induced X-ray emission (PIXE), which has no depth resolution but can unambiguously identify elements and analyse for trace elements with detection limits approaching μg/g, was used. For Al-doped fibres, the dopant concentration in the range 0.98–2.93 mol% have been estimated, with equivalent range for Ge-doped fibres being 0.53–0.71 mol%. In making central-axis irradiation measurements a solid water™ phantom was used. For 6-MV photons and electron energies in the range 6, 9 and 12 MeV, a source to surface distance of 100 cm was used, with a dose rate of 400 cGy/min for photons and electrons. The TL measurements show a linear dose–response over the delivered range of absorbed dose from 1 to 4 Gy. Fading was found to be minimal, less than 10% over five days subsequent to irradiation. The minimum detectable dose for 6-MV photons was found to be 4, 30 and 900 μGy for TLD-100 chips, Ge- and Al-doped fibres, respectively. For 6-, 9- and 12-MeV electron energies, the minimum detectable dose were in the range 3–5, 30–50 and 800–1400 μGy for TLD-100 chip, Ge-doped and Al-doped fibres, respectively.     

A comparison of the performance characteristics of four film dosimeters in a 10-MeV electron beam.

Performance characteristics of four routine film dosimeters (CTA, B-3, PVC and LiF (Sunna)) in a 10-MeV electron beam were investigated. Dose response curves for the range 5-40kGy are presented. The dose response curve is linear for the CTA film, supralinear for the LiF (Sunna) film and sublinear for the B-3 and PVC films. The low sensitivity of the CTA film to ionizing radiation restricts its use to high doses, while the supralinear response curve of the LiF (Sunna) dosimeter allows this film to be used only in measurements of low doses. The optical absorption temperature coefficients for the CTA, B-3 and LiF (Sunna) films were found to be at the level of +/-0.1%/( composite function)C. The temperature coefficient for the PVC film decreased from +0.35%/( composite function)C immediately after irradiation to +0.04%/( composite function)C three months later. Because of the significant time dependence of the PVC film signal, a careful standardization of the heating regimen and of the time between the irradiations and measurements is necessary.     

Thermoluminescent detector performance in low-dose slow-rate environments

This study is concerned with the use of Thermoluminescent Detectors (TLDs) in low-dose and slow-rate radiation environments, as encountered by manned or unmanned satellites in space. In the first phase of this work, samples of four types of TLDs (LiF and CaF₂ of small and large size) were exposed to an absorbed dose rate of 10 μGy/min (1 mrad/min) of ⁶⁰Co γ rays at irregular, intermittent intervals for a total of 62 min/day. Irradiations lasted for seven days and were followed by one day of annealing at room temperature, prior to the final measurements. Results show that the larger size TLDs followed the expected linear increases of light output with dose for each day without indication of either fading (due to the relatively long time period between irradiations) or discrepancies (due to the low dose rates in comparison to background and noise), whereas the smaller samples deviated significantly from the linear increase of a projected dose-per-day curve, implying an effective and substantial daily fading process in the slow-rate environment. These latter results, however, need further investigation. Some contributing sources of error in the small LiF dosimeters have been identified, such as the existence of high temperature traps in the 400°–600°C temperature range. Conclusions and recommendations are presented.     

Thermoluminescence property of LiMgF3 erbium activated phosphor

The perovskite-like LiMgF(3):ErF(3) pellets were obtained from the melt formed by LiF and MgF(2) mixed salts in the stoichiometric ratio. The perovskite material was doped with 1, 2 and 4 mol% of ErF(3) impurity. The pellets samples were (60)Co gamma irradiated and their thermoluminescence (TL) properties were analyzed, i.e., dose-response, fading at RT and under UV irradiation, TL signal reproducibility, and kinetic parameters. The intensity of the TL response against irradiation dose was increased remarkably by the high concentration of impurity, and a linear dose-response was observed in the range of 1-10 Gy. The fading observed at RT was about 10-30% after 24h from irradiation. All samples were exposed from 1 to 200 Gy gamma dose range. The TL glow peaks were found around 367-376, 438-447, 509-521, and 594-611 K, when the doped samples were 1, 2 and 4 mol% of the erbium impurity concentration. The thermoluminescence kinetics parameters of the glow curves have been analyzed using the Computerized Glow Curve Deconvolution (CGCD) method.     

A personal thermoluminescence dosimeter using LiF:Mg,Cu,Na,Si detectors for photon fields.

A new personal thermoluminescence (TL) dosimeter for photon fields using LiF:Mg,Cu,Na,Si TL detector was developed by taking advantage of its dosimetric properties including energy dependencies. Solid pellet type LiF:Mg,Cu,Na,Si detector was developed and fabricated at Korea Atomic Energy Research Institute (KAERI) and has been studied on its dosimetric properties such as TL grow curve, dose response, energy response and reusability. Its dosimetric properties show the feasibility of application of LiF:Mg,Cu,Na,Si TL detector to personal dosimetry fields. A new dosimeter using LiF:Mg,Cu,Na,Si TL detector was designed and tested through irradiation experiments. This multi-element TL dosimeter allows the measurement of a personal dose equivalent Hp(d) in photon fields. Based on the experimental results of the proposed dosimeter, it was demonstrated that a personal TL dosimeter using sintered LiF:Mg,Cu,Na,Si TL detector is appropriate to estimate personal dose equivalent for wide range energy of photon fields.     

Further studies on higher temperature TL glow peaks of 7LiF:Mg,Ti

Thermoluminescence (TL) characteristics of the higher temperature peaks of LiF:Mg,Ti, which exhibit a unique property of high relative response to high LET radiation, were studied in view of some recent findings and discussions. By making separate readouts of dosimetric peaks (mainly peak 5) and higher temperature peaks (mainly peak 7), the precision in TL measurements, reusability and, fading were found comparable for the TL readouts in the two regions. However, the intensity of higher temperature peaks was found to be susceptible to the annealing treatments. In the standard annealing treatment of LiF:Mg,Ti, namely, 400 °C for 1 h followed by 100 °C for 2 h, the intensity of the higher temperature glow peaks was significantly affected when the second step of lower temperature annealing treatment at 100 °C for 2 h was not used. The dose response function f(D) of higher temperature peaks to gamma rays in the range from 30 to 150 mGy was found to be within about 10% (−4 and +9%) but above 200 mGy it increased sharply. The intricacies of dosimetry of mixed fields of low and high LET radiation are discussed.     

The thermoluminescent properties of Brazilian topaz

The TL properties of Brazilian topaz were investigated. The glow curve up to 573 K presents peaks close to 373, 403, 473 and 523 K. A linear response from 7 to at least 10⁴ mGy is observed. The TL sensitivity is about 150 times lower than that of LiF—TL 100 Harshaw. The fading behaviour was investigated during a period of 15 days, at room temperature. The third peak intensity, after 24 h, becomes 80% of its initial value and then seems to stabilize.     

Dose-response and intrinsic efficiency of thermoluminescent dosimeters in a 15 MV clinical photon beam in a liquid water phantom

This paper compares the performance of CaSO4:Dy and LiF dosimeters irradiated with a 15 MV photon beam of a clinical linear accelerator to 0.1-10 Gy in a liquid water. The dose-response curves are linear up to 5 Gy. The average TL sensitivity of CaSO4:Dy is 26 and 287 times higher than the sensitivities of LiF:Mg,Ti and microLiF:Mg,Ti, respectively. CaSO4:Dy has an intrinsic efficiency 71% and 94% higher than the intrinsic efficiencies of LiF:Mg,Ti and microLiF:Mg,Ti, respectively.     

Characterization of the glow-peak fading properties of six common thermoluminescent materials

The pre-irradiation and post-irradiation fading rates of the thermoluminescent glow peaks of six commonly used thermoluminescent dosimeters under controlled environmental conditions over approximately 30 d are examined. Glow peaks were fit to the first-order kinetics model using a computerized glow curve deconvolution program. Dosimeters studied were LiF:Mg,Ti, CaF₂:Dy, CaF₂:Tm, CaF₂:Mn, LiF:Mg,Cu,P, and CaSO₄:Dy. LiF:Mg,Ti and LiF:Mg,Cu,P experienced significant pre-irradiation fading. All types except CaF₂:Mn experienced post-irradiation fading. Ratios of glow-peak areas were fit to exponential decay functions when possible.     

A search for novel thermoluminescent radiation dosimeter media

We describe two example pilot efforts to help define new thermoluminescent dosimeter media. The first concerns ZnS:Mn nanophosphors, prepared by chemical precipitation using zinc and sodium sulfate, doped with manganese sulfate at concentrations varying from 1 to 3 mol. The second concerns chemical vapor deposited diamond, produced as a thin film or as amorphous carbon on a single-crystal silicon substrate, each deposited under the same conditions, use being made of the hot filament-chemical vapor deposition (HFCVD) technique. The gas concentrations used were 1% CH₄ in 99% H₂ and 25% CH₄ in 75% H₂. Characterization of formations used FESEM, XRD and EDX. The nanophosphors consisted of particles of sizes in the range 85–150 nm, the thermoluminescence (TL)-based radiation detection medium giving rise to a single peaked glow curve of maximum yield at a temperature of 250 °C at a heating rate of 5 °C/s. The TL response increased linearly with radiation dose, ZnS doped to 2 mol of Mn being found the most sensitive. Regarding chemical vapor deposited (CVD) carbon, inappreciable TL was found for the resultant ball-like amorphous carbon films, graphite, and the silicon substrate, whereas CVD diamond films showed a promising degree of linearity with dose. For both the ZnS and diamond samples, TL signal fading was appreciable, being some 40% per day for ZnS and>50% per day for CVD films even under storage in the dark at room temperature, making it apparent that there is need to adjust parameters such as the size of nanoparticles.     

Fading characteristics of an alanine-polystyrene dosimeter

Alanine dosimetry is useful for transfer dosimetry by long distance mailing, because of its stability. It has the advantage that the measurement of electron spin resonance (ESR) spectral signal is non-destructive to the dosimeter, with the promise that the method may supply archival dosimetry data, depending on the degree of post-irradiation stability of the signal. The effects of temperature during irradiation and storage on fading of the ESR signal were studied using an alanine dosimeter molded with polystyrene (alanine-PS dosimeter). This investigation covered a long range of storage time (up to 160 days) after irradiation to absorbed doses in the range 1 to 100 kGy, for application to transfer dosimetry between Japan and neighboring Asian countries.Dose response of an alanine-PS dosimeter depends on the temperature during irradiation. The same temperature coefficient of +0.24%/°C was measured at different dose levels of 1, 10 and 100 kGy administered at a constant dose rate of 7 kGy/h. Fading of the dose response was measured under storage at various temperatures (5–40°C). The fading curve generally has two phases with fast and slow fading rates. The response of an alanine dosimeter is relatively stable for doses of 1.4 and 14 kGy, when stored at temperatures below 25°C. However, the degree of fading was roughly 3 and 5% under a storage temperature of 40°C for 5 and 100 days, respectively, after irradiation to 14 kGy. The fading percentages at 100 kGy were 2 and 4% (after 5 days) and 6 and 15% (after 100 days) under the storage temperature of 25 and 40°C, respectively. The fading rates have a relatively small dependence on irradiation temperature. This is observed even when irradiation are made at high temperatures (60°C) and for the doses 100 kGy and above. The mechanism of decay of radicals is discussed to explain the fading characteristics of the two phases of fading. The alanine-PS dosimeter is useful for transfer standard dosimetry up to a dose level of 10 kGy when stored after irradiation at temperature below 40°C. However, consideration of temperature effects during and after irradiation is vital for accurate transfer dosimetry of high doses, especially in the southern Asian countries.     

Dosimetric study of thermoluminescent detectors in clinical photon beams using liquid water and PMMA phantoms

The purpose of this study was the dosimetric evaluation of thermoluminescent detectors of calcium sulphate doped with dysprosium (CaSO4:Dy) produced by IPEN compared to the TL response of lithium fluoride doped with magnesium and titanium (LiF:Mg,Ti) dosimeters and microdosimeters produced by Harshaw Chemical Company to clinical photon beams dosimetry (6 and 15 MV) using liquid water and PMMA phantoms.     

Dose measurements using thermoluminescent dosimeters and DoseCal software at two paediatric hospitals in Rio de Janeiro.

A dosimetric survey in paediatric radiology is currently being carried out at the paediatric units of two large hospitals in Rio de Janiero city: IPPMG (Instituto de Pediatria e Puericultura Martag?o Gesteira, University Hospital of Federal University of Rio de Janeiro) and IFF (Instituto Fernandes Figueira, FIOCRUZ). Chest X-ray examination doses for AP, PA and LAT projections of paediatric patients have been obtained with thermoluminescent dosimeters (TLDs) and with use of a software package DoseCal. In IPPMG and IFF 100 patients have been evaluated with the use of the TLDs and another group of 100 patients with the DoseCal software. The aim of this work was to estimate the entrance skin dose (ESD) for frontal, back and lateral chest X-rays exposure of paediatric patients. For ESD evaluation, three different TL dosimeters have been used, namely LIF:Mg,Ti (TLD100), CaSO4:Dy and LiF:Mg,Cu,P (TLD100H). The age intervals considered were 0-1, 1-5, 5-10 and 10-15 years. The results obtained with all dosimeters are similar, and it is in good agreement with the DoseCal software, especially for AP and PA projections. However, some larger discrepancies are presented for the LAT projection.     

The gamma-ray response of clear polymethylmethacrylate dosimeter radix RN15®

Basic characteristics of different batches of Radix RN15® dosimeter, a commercially available undyed polymethylmethacrylate dosimeter, was studied for its application to process control of radiation sterilization. Radix has relatively small deviation of thickness, optical absorption spectrum, and optical density values before irradiation. The response curves, in terms of net optical density per unit thickness (ΔOD/mm) as a function of absorbed dose, D_PMMA, are nearly linear up to 15 kGy and become sublinear at higher doses. Scattering of dose response in 5 dosimeter replicates is ± 1% (1 σ). The dose-response slope at 25 kGy while held at irradiation temperatures in the range 0–60°C, relative to those under 25°C, increases with temperature up to 40°C, the maximum point, and decreases at higher temperatures. Over the temperature range of 10–50°C, the variation with temperature of evaluated dose derived from the calibration curve at 25°C is less than 5% when using a dose rate of 6 kGy/h. At lower dose rates (e.g. 0.7 kGy/h) the irradiation temperature dependence is negligible over this temperature range. The temperature dependence at 40 kGy is less severe than that at 25 kGy. The post-irradiation stability of dose response is less than 5% for more than 100 h after 25 kGy irradiation and storage at 0–35°C. The change in optical density of unirradiated dosimeters 3 years after manufacturing is negligible when the dosimeters are stored at controlled laboratory conditions of temperature (25°C) and relative humidity (40%). The 3-year-old dosimeters by irradiation to a dose of 25 kGy show about 2% lower response than that at 25 kGy at the beginning of the 3-year period.     

CaSO4 (Dy) thermoluminescent dosimeters for the determination of gonadal doses.

For the measurement of gonadal doses sensitive dosimeters are necessary. Since CaSO4 (Dy) thermoluminescent dosimeters are very sensitive the energy dependence has been measured as compared to LiF in the tube potential region between 50 and 150 kV. Moreover the output of the LiF dosimeters was compared with the results of ionization chamber measurements. Although the energy dependence of CaSO4 (Dy) is well-known the actual dependence on the potential appears to be within +/- 10% for moderately filtered beams in the region from 50 to 150 kV.