Thin layer alpha-Al2O3:C beta dosemeters for the assessment of current dose rate in teeth due to 90Sr intake,and comparison with electron paramagnetic resonance dosimetry

The use of thin-layer alpha-Al2O3:C thermoluminescent detectors (TLDs) for the assessment of current beta dose rate in human teeth due to 90Sr intake is investigated. The teeth used in this study were collected from members of the Techa river population who were exposed to radiation as a result of releases of the Mayak plutonium production facilities (Southern Urals-Russia) between 1949 and 1956. The beta dose rates from different parts of the tooth (enamel, crown dentine, and root) were determined by storing the detectors over the samples in a shielded environment. The cumulative dose measured by electron paramagnetic resonance (EPR) in different dental tissues is found to be proportional to current dose rate obtained from alpha-Al2O3:C thermoluminescence dosemeters. The retention of 90Sr in various parts of the teeth is discussed.     

Monte Carlo calculation and experimental verification of the photon energy response of tooth enamel in a head-sized plexiglas phantom

The use of electron paramagnetic resonance (EPR) tooth dosimetry for calculation of organ doses requires conversion of the measured absorbed dose in enamel. Before deriving conversion factors from simulation calculations with a realistic anthropomorphic human phantom, in the current study a simplified phantom was chosen to compare EPR measurement and Monte Carlo calculation. The dose response of tooth enamel of molars at various positions inside a cylindrical Plexiglas phantom of head-size was calculated hy Monte Carlo modelling in parallel photon beams of X rays of 63 keV equivalent energy and 60Co gamma rays (1.25 Mev). For X ray exposure, preliminary results of EPR dosimetry with tooth enamel samples prepared from molars irradiated in the phantom were in agreement with calculation. The mean value of the ratio of the measured to the calculated dose was 0.93 +/- 0.08.     

Dose reconstruction with electron paramagnetic resonance spectroscopy of deciduous teeth

In the present study the feasibility of using whole, naturally loose deciduous incisors for dose reconstruction with electron paramagnetic resonance (EPR) spectroscopy was investigated. The properties of EPR signals were analysed before and after laboratory irradiation. The parameters of the native EPR signal of deciduous incisors was found to be different from those from enamel of permanent molars. The native EPR signal of deciduous incisors with peak-to-peak line width of 0.65 mT was located at g = 2.0050. The evaluated parameters of the dosimetric EPR signal (CO2-) of deciduous incisors were in agreement with those for enamel of permanent molars. A detection threshold for absorbed dose of about 100 mGy was estimated.     

Calibration of EPR signal dose response of tooth enamel to photons: experiment and Monte Carlo simulation

The experimental energy dependence of the electron paramagnetic resonance (EPR) radiation-induced signal at irradiation by photons in the energy range of 13 keV-1.25 MeV was analysed in terms of the absorbed dose in human tooth enamel. The latter was calculated using a Monte Carlo simulation of the photon and electron transport. The dependence of the calculated absorbed dose on the sample thickness was analysed. No energy dependence of the EPR signal on the absorbed dose in enamel was verified in the range of 37 keV-1.25 MeV. At 13 and 20 keV the EPR signal dose response was reduced by 8% probably due to sample powdering. Dose-depth profiles in enamel samples irradiated by 1.25 MeV photons in polymethylmethacrylate and aluminium build-up materials were calculated. It was concluded that secondary electron equilibrium conditions are better fulfilled for irradiation in aluminium, which makes this material preferable for calibration.     

Quantification of low dose signal in EPR tooth dosimetry--a novel approach

For radiation exposures below 100 mGy, the dosimetric signal in tooth enamel is too small to be measured by using the traditional dose reconstruction procedure. This is because low amplitude zero-added-dose signal can not be identified in an EPR spectrometer. A technique is presented wherein, zero-added-dose signal. when amplified by a proper known dose, can be measured in the EPR spectrometer. Mathematically, the accidental dose x is modified by a known amount of exposure, y (large enough so that the signal is now visible), and total exposure becomes x' = x + y, which is the modified-zero-added dose. The exposure x' is then quantified using the conventional backward extrapolation method and the accidental dose can be measured. In a laboratory controlled experiment, the feasibility of dose reconstruction in the 100 mGy range has been demonstrated. This may enable measurements of dose even due to suspected low exposure in tooth enamel.     

Review of reconstruction of radiation incident air kerma by measurement of absorbed dose in tooth enamel with EPR

Electron paramagnetic resonance dosimetry with tooth enamel has been proved to be a reliable method to determine retrospectively exposures from photon fields with minimal detectable doses of 100 mGy or lower, which is lower than achievable with cytogenetic dose reconstruction methods. For risk assessment or validating dosimetry systems for specific radiation incidents, the relevant dose from the incident has to be calculated from the total absorbed dose in enamel by subtracting additional dose contributions from the radionuclide content in teeth, natural external background radiation and medical exposures. For calculating organ doses or evaluating dosimetry systems the absorbed dose in enamel from a radiation incident has to be converted to air kerma using dose conversion factors depending on the photon energy spectrum and geometry of the exposure scenario. This paper outlines the approach to assess individual dose contributions to absorbed dose in enamel and calculate individual air kerma of a radiation incident from the absorbed dose in tooth enamel.     

Diagnostic X ray dose profiles in molar teeth using Monte Carlo simulation

The dose profiles in molar teeth from diagnostic X rays was calculated using the Monte Carlo software program MCNP4c2. The information calculated supports needs in EPR retrospective dosimetry to account for diagnostic X ray exposures in teeth. Only tooth positions 6, 7 and 8 were simulated (the three teeth furthest back including the wisdom teeth) using a very detailed model of the pertinent physiology. The lingual and buccal halves of teeth were evaluated as were the crown dentin and roots in tooth position 7. Linear dose profiles through the enamel were also calculated.     

EPR dosimetry in a mixed neutron and gamma radiation field

Suitability of Electron Paramagnetic Resonance (EPR) spectroscopy for criticality dosimetry was evaluated for tooth enamel, mannose and alanine pellets during the 'international intercomparison of criticality dosimetry techniques' at the SILENE reactor held in Valduc in June 2002, France. These three materials were irradiated in neutron and gamma-ray fields of various relative intensities and spectral distributions in order to evaluate their neutron sensitivity. The neutron response was found to be around 10% for tooth enamel, 45% for mannose and between 40 and 90% for alanine pellets according their type. According to the IAEA recommendations on the early estimate of criticality accident absorbed dose, analyzed results show the EPR potentiality and complementarity with regular criticality techniques.     

Retrospective dosimetry using synthesized nano-structure hydroxyapatite

Micro and nano-structure hydroxyapatite samples were synthesized via several different methods. The samples were characterised utilising the Fourier transmission infra-red, scanning electron microscope and X-ray diffraction methods, to find out the structure most similar to human tooth enamel, and the best method was found. The electron paramagnetic resonance (EPR) signals of the gamma-irradiated samples were measured using an EPR spectrometer system. A calibration curve was established by irradiation of the samples at four doses of 50-500 mGy. The parameters of the calibration curve, slope and intercept with dose axis are determined by linear regression analysis. This calibration curve can be used for human tooth enamel for retrospective dosimetry purposes.     

Possibilities of using human teeth for retrospective dosimetry: analysis of the Techa River data

Different methods for utilising teeth were applied for the reconstruction of internal and external doses for the population of the Techa riverside area contaminated as a result of radioactive releases from the Mayak plutonium-production facility. Information on 90Sr content in the enamel of teeth obtained from the Techa River residents has been used for the reconstruction of intakes of this nuclide. Analyses of dosimetric investigations on dental tissues performed in the Techa River region provide an understanding of the possibilities and limitations of using human teeth in retrospective dosimetry studies.     

Gamma-irradiated EPR response of nano-structure hydroxyapatite synthesised via hydrolysis method

In this paper, the gamma-irradiated EPR responses of hydroxyapatite (HAP) samples were investigated from a dosimetric point of view. For this purpose, nano-structure hydroxyapatite was synthesised via a hydrolysis method. A portion of the produced powder was annealed at 600 °C for 4 h. All the samples were irradiated under the (60)Co gamma-ray source at different absorbed doses from 0.1 to 45 kGy. EPR signal intensities of HAP samples were measured at room temperature in air. Subsequently, the EPR signal intensities were constructed as a function of radiation dose and were compared with the results of bone powder samples. The results show that the EPR responses of non-annealed HAP samples are higher than others for several times.     

Relations between tooth enamel dose and organ doses for electron spin resonance dosimetry against external photon exposure

An analysis of doses to tooth enamel and to organs was carried out to develop a method that can predict the organ doses and the effective dose by electron spin resonance (ESR) dosimetry using tooth samples for external photon exposure. Absorbed dose to tooth enamel and organ doses were obtained by Monte Carlo calculations using the EGS4 code in combination with a mathematical human model with a newly defined teeth part. The calculations gave quantitative relations between tooth enamel dose and organ doses for some cases of external photon exposure. It was also found that tooth enamel dose depends more significantly on energy of incident photons than the other organ dose or the effective dose. The obtained data are to be useful for the assessment of individual dose in past exposure events by the ESR dosimetry using tooth enamel.     

The Third International Intercomparison on EPR Tooth Dosimetry: part 2, final analysis

The objective of the Third International Intercomparison on EPR Tooth Dosimetry was to evaluate laboratories performing tooth enamel dosimetry <300 mGy. Final analysis of results included a correlation analysis between features of laboratory dose reconstruction protocols and dosimetry performance. Applicability of electron paramagnetic resonance (EPR) tooth dosimetry at low dose was shown at two applied dose levels of 79 and 176 mGy. Most (9 of 12) laboratories reported the dose to be within 50 mGy of the delivered dose of 79 mGy, and 10 of 12 laboratories reported the dose to be within 100 mGy of the delivered dose of 176 mGy. At the high-dose tested (704 mGy) agreement within 25% of the delivered dose was found in 10 laboratories. Features of EPR dose reconstruction protocols that affect dosimetry performance were found to be magnetic field modulation amplitude in EPR spectrum recording, EPR signal model in spectrum deconvolution and duration of latency period for tooth enamel samples after preparation.     

Gamma-ray and neutron dosimetry by EPR and AMS, using tooth enamel from atomic-bomb survivors: a mini review

The electron paramagnetic resonance (EPR, or electron spin resonance) method was used to measure CO??· radicals recorded in tooth enamel by exposure to atomic-bomb gamma rays. The EPR-estimated doses (i.e. ??Co gamma-ray equivalent dose) were generally in good correlation with cytogenetic data of the same survivors, whereas plots of EPR-estimated dose or cytogenetically estimated dose against DS02 doses turned out to scatter more widely. Because those survivors whose EPR doses were higher (or lower) than DS02 doses tended to show also higher (or lower) responses for cytogenetic responses, the apparent variation appears primarily due to problems in individual DS02 doses rather than the measurement errors associated with the EPR or cytogenetic technique. A part of the enamel samples were also used for evaluation of neutron doses by measuring ?1Ca/??Ca ratios using the accelerator mass spectrometry technique. The results for the measured ratios were on average ~85 % of the calculated ratios by DS02 (but within the 95 % confidence bounds of the simulated results), which lends support to DS02-derived neutron doses to the survivors.     

Organ dose conversions from ESR measurements using tooth enamel of atomic bomb survivors

Dose conversions were studied for dosimetry of atomic bomb survivors based upon electron spin resonance (ESR) measurements of tooth enamel. Previously analysed data had clarified that the tooth enamel dose could be much larger than other organ doses from a low-energy photon exposure. The radiation doses to other organs or whole-body doses, however, are assumed to be near the tooth enamel dose for photon energies which are dominant in the leakage spectrum of the Hiroshima atomic bomb assumed in DS02. In addition, the thyroid can be a candidate for a surrogate organ in cases where the tooth enamel dose is not available in organ dosimetry. This paper also suggests the application of new Japanese voxel phantoms to derive tooth enamel doses by numerical analyses.     

Electron paramagnetic resonance of human tooth enamel at high gamma ray doses

Powdered human tooth enamel was exposed to 60Co gamma rays up to a dose of 100 kGy. The electron paramagnetic resonance (EPR) signal intensity (1) of the radiation-generated carbon dioxide radicals was measured for dependence on absorbed dose (D). The EPR dose response can be fitted with an exponential saturation function I = I(M)[1 - exp(-D/D37)] with the saturated signal intensity (I(M)) and the dose saturation value (D37). The obtained value D37 = 9.64 (+/- 0.96) kGy (measured at least one month after irradiation) exceeds those given in the literature. The saturated concentration of orthorhombic CO2- radicals was estimated at 6.5 x 10(17) per gram of enamel by comparing the integrated EPR spectra of enamel and a standard MgO:Cr probe. For enamel samples, which were heated before irradiation for one hour at +405 degrees C, the value of D37T = 3.89 (+/- 0.44) kGy and the saturated value of CO2- radicals 3.4 x 10(17) per gram of enamel were lower than for unheated samples. The initial rise of the signal with the dose was slightly higher (8.8 x 10(13) radicals/g x Gy) for heated compared with unheated samples (6.8 x 10(13) radicals/g x Gy).     

Optimisation of recording conditions for the electron paramagnetic resonance signal used in dental enamel dosimetry

Optimisation of the parameters for recording the electron paramagnetic resonance (EPR) spectra of dental enamel for absorbed dose reconstruction was performed for an EMX (Bruker) spectrometer supplied with a high-sensitivity microwave cavity. Dose determination was performed using a previously developed automatic spectra processing procedure, which uses the non-linear fit of a model spectrum. The experimental error was estimated as the standard deviation of the results from the nominal doses for the set of spectra recorded for 10 samples prepared from teeth of different persons and irradiated in the dose range 0-500 mGy. The microwave power and magnetic field modulation amplitude corresponding to the minimum of dependencies of the error on these parameters were adopted as the optimal ones. For the sets of spectra recorded at optimal parameters for sample masses 100, 50 and 30 mg, the errors of dose determination were obtained as 18, 27 and 37 mGy respectively.     

Influence of thermal treatments on the response of sand radiation detectors for high-dose dosimetry

The dosimetric properties of sand from Brazilian beaches have shown to be useful for high-dose dosimetry. The thermoluminescent (TL) and electron paramagnetic resonance (EPR) techniques were utilised, and the sand samples were recently studied in relation to their main dosimetric properties. The EPR signal at g = 1.999 grows significantly in function of the absorbed dose, and the TL peaks appear at 110 and 170 degrees C. However, these sand samples present a post-irradiation thermal decay at room temperature, which is a problem for dosimetric procedures. In this study, sand samples have been studied in relation to different thermal treatments. Post-irradiation treatments were performed at 50 degrees C up to 230 degrees C.     

An in vitro L-band electron paramagnetic resonance study of highly irradiated whole teeth

Regarding in vivo L-band dosimetry with human teeth, a number of preliminary experiments were carried out that were linked to the resonators response and the relative contribution of enamel to the EPR signal intensity of irradiated whole teeth. The sensitivity of the extended loop resonator varies in the antenna plane, but this variation tends to vanish when the sample is moved away from this plane. When the loop antenna is placed just above the highly irradiated molar, around 88% of the dosimetric signal is due to the crown enamel. The sensitivity inside a birdcage cavity is approximately equal over the volume of a molar; only 30% of the molar's total dosimetric signal results from enamel. Some decrease in the intensity of the dosimetric signal from enamel is observed after irradiation. At room temperature, the signal is reduced by about 20% within 90 days and approaches a plateau with a time constant of about 35 days.     

Dosimetric calculations for uranium miners for epidemiological studies

Epidemiological studies on uranium miners are being carried out to quantify the risk of cancer based on organ dose calculations. Mathematical models have been applied to calculate the annual absorbed doses to regions of the lung, red bone marrow, liver, kidney and stomach for each individual miner arising from exposure to radon gas, radon progeny and long-lived radionuclides (LLR) present in the uranium ore dust and to external gamma radiation. The methodology and dosimetric models used to calculate these organ doses are described and the resulting doses for unit exposure to each source (radon gas, radon progeny and LLR) are presented. The results of dosimetric calculations for a typical German miner are also given. For this miner, the absorbed dose to the central regions of the lung is dominated by the dose arising from exposure to radon progeny, whereas the absorbed dose to the red bone marrow is dominated by the external gamma dose. The uncertainties in the absorbed dose to regions of the lung arising from unit exposure to radon progeny are also discussed. These dose estimates are being used in epidemiological studies of cancer in uranium miners.