Deconvolution of complex EPR spectrum of tooth enamel into three components: native,dosimetric and mechanical

A software was developed on the base of non-linear simulation, which allowed the deconvolution of EPR spectra of tooth enamel into three components: native, radiation- and mechanically induced. The software was designed for the reconstruction of individual absorbed doses by EPR spectra of tooth enamel using the method of additive irradiation of samples. It has been demonstrated with the help of this program that the presence of mechanically induced paramagnetic centers in enamel samples led to an excessive individual absorbed dose reconstructed by EPR spectra of tooth enamel.     

Feasibility of Q-Band EPR Dosimetry in Biopsy Samples of Dental Enamel, Dentine and Bone

Electron paramagnetic resonance (EPR) dosimetry of tooth enamel in X-band has been established as a suitable method for individual reconstruction of doses 0.1 Gy and higher. The objective was to demonstrate the feasibility of using Q-band EPR in small biopsy tooth enamel samples to provide accurate measurements of radiation doses. Q-band spectra of small (<10 mg) irradiated samples of dentine and bone were studied to investigate the possibility of using Q-band EPR for dose measurements in those materials if there are limited amounts of enamel available, and there is no time for the chemical sample preparation required for accurate X-band measurements in dental enamel. Our results have shown that Q-band provides accurate measurements of radiation doses higher than 0.5 Gy in tooth enamel biopsy samples as small as 2 mg. Q-band EPR spectra in powdered dentine and bone demonstrated significantly higher resolution and sensitivity than in conventional X-band measurements.     

Analysis of EPR tooth enamel spectra exposed to combined radiation and mechanical effects

In the EPR spectra of tooth enamel samples exposed to sequential radiation and mechanical effect, the intensity of the signal in the spectra of tooth enamel samples exposed to sequential mechanical and radiation effects exceeded the amplitude of a signal in enamel samples that were only exposed to radiation. The increased dosimetric signal can be explained by superposition of mechanically and radiation-induced signals. The contribution of the mechanically induced component to the individual dose load reconstructed by EPR-spectra of tooth enamel has been evaluated.     

Interlaboratory comparison of tooth enamel dosimetry on Semipalatinsk region: Part 1, general view

For intercomparison of methods of dose determination using electron paramagnetic resonance (EPR) spectroscopy of tooth enamel, the same sets of enamel samples were analyzed in different laboratories using similar recording parameters. The sets of samples included calibration samples irradiated in known doses, test samples irradiated to doses unknown to the participants and accidental dose samples prepared from teeth of humans affected by radioactive fallout from nuclear tests in the Semipalatinsk Nuclear Test Site in Kazakhstan. The test samples were analyzed to determine the differences in the resulting doses using different spectrometers and different spectra processing methods. The accidental dose samples were analyzed in order to test the precision of doses determined by EPR spectroscopy and to obtain more accurate values by averaging the results from different laboratories.     

Electron paramagnetic resonance radiation dosimetry in fingernails

There is now an increased need for accident dosimetry due to the increased risk of significant exposure to ionizing radiation from terrorism or accidents. In such scenarios, dose measurements should be made in individuals rapidly and with sufficient accuracy to enable effective triage. Electron paramagnetic resonance (EPR) is a physical method of high potential for meeting this need, providing direct measurements of the radiation-induced radicals, which are unambiguous signatures of exposure to ionizing radiation. For individual retrospective dosimetry, EPR in tooth enamel is a proven and effective technique when isolated teeth can be obtained. There are some promising developments that may make these measurements feasible without the need to remove the teeth, but their field applicability remains to be demonstrated. However, currently it is difficult under emergency conditions to obtain tooth enamel in sufficient amounts for accurate dose measurements. Since fingernails are much easier to sample, they can be used in potentially exposed populations to determine if they were exposed to life-threatening radiation doses. Unfortunately, only a few studies have been carried out on EPR radiation-induced signals in fingernails, and, while there are some promising aspects, the reported results were generally inconclusive. In this present paper, we report the results of a systematic investigation of the potential use of fingernails as retrospective radiation dosimeters.     

EPR dosimeter material properties of potassium tartrate hemihydrate

The ability of potassium tartrate hemihydrate as a radiation sensitive material for electron paramagnetic resonance (EPR) dosimetry was investigated. The samples were subjected to different doses, in the range of 1–9 Gy of ⁶⁰Co gamma rays at room temperature. The EPR spectra were investigated through variation of signal intensity with respect to absorbed dose, magnetic field modulation amplitude, microwave power and time stability. The results indicate that the sensitivity of potassium tartrate hemihydrate is about 30% higher than that of alanine. However, the EPR signal is timely less stable within the first two weeks after irradiation.     

Signal processing for radiation dosimetry using EPR in dental enamel: comparison of three methods

We are reporting an alternative method of extracting useful dose information from complex EPR spectra of dental enamel. Digital differentiation of the initial first derivative spectrum followed by filtering is used to clearly distinguish the radiation-induced signal from the native background signal. The peak-to-peak height of the resulting second derivative of the signal is then measured as an indication of absorbed dose. This method does not require preliminary elimination of the native background signal, and is not effected by any uncertainty in the determination of the background signal or by errors resulting from the subtraction of two signals of comparable magnitude. Ten enamel samples were irradiated with known doses in the range of 250–10⁵ mGy. There was agreement for all the samples, within the typical experimental error of ±10% for EPR dosimetry in dental enamel, between the doses determined by two common techniques using native signal subtraction and the doses determined by the new second derivative method proposed here.     

ISS protocol for EPR tooth dosimetry

The accuracy in Electron Paramagneetic Resonance (EPR) dose reconstruction with tooth enamel is affected by sample preparation, dosimetric signal amplitude evaluation and unknown dose estimate. Worldwide efforts in the field of EPR dose reconstruction with tooth enamel are focused on the optimization of the three mentioned steps in dose assessment. In the present work, the protocol implemented at ISS in the framework of the European Community Nuclear Fission Safety project “Dose Reconstruction” is presented. A combined mechanical–chemical procedure for ground enamel sample preparation is used. The signal intensity evaluation is carried out with powder spectra simulation program. Finally, the unknown dose is evaluated individually for each sample with the additive dose method. The unknown dose is obtained by subtracting a mean native dose from the back-extrapolated dose. As an example of the capability of the ISS protocol in unknown dose evaluation, the results obtained in the framework of the 2nd International Intercomparison on EPR tooth enamel dosimetry are reported.     

EPR dose reconstruction of two Kazakh villages near the Semipalatinsk nuclear test site

Electron paramagnetic resonance (EPR) dose reconstruction has been performed on archived tooth samples from residents of two villages near the Semipalatinsk nuclear test site in Kazakstan. The context of this work is a large multidisciplinary study of thyroid disease prevalence and radiation dose among long-term residents of villages near that nuclear test site, in which EPR is used for biodosimetric validation of the gamma-ray component of dose reconstruction algorithms applied to the data for various villages whose residents were exposed to radioactive fallout during 1949–1962, the period of above-ground atomic bomb testing. The tooth samples, nine from the village of Kainar and 23 from the village of Znamenka, were extracted in 1964 and 1967, respectively, and stored indoors in closed boxes in Semipalatinsk. According to provided information, some time in the past, the teeth from Kainar were heated to 80°C for one day. Experiments carried out on 12 teeth from US sources to determine the effects of long-term storage and heat treatment found that EPR assay findings were not compromised for storage times less than 35 years and annealing at temperatures below 200°C. For tooth enamel samples prepared from molars and premolars the average reconstructed gamma dose was 390±70 mGy for Kainar residents and 95±40 mGy for Znamenka residents.     

EPR-dosimetry with carious teeth

The effect of caries in EPR dosimetry of tooth enamel (in the dose range of 0–1 Gy) was investigated. The enamel of each tooth was divided into carious, non-carious and intermediate portions. The EPR signals of enamel at g = 2.0018 (dosimetric) and g = 2.0045 (native) were examined. The intensity of the dosimetric signal was the same for all three portions, while that of the native signal was higher for carious portions than for non-carious and intermediate portions. Reconstruction of the laboratory applied doses was done using all portions. Reasonable correlation between nominal and reconstructed doses was found in most cases. The effect of alkali treatment on the native and dosimetric signals of enamel was also tested. Reduction of the native signal intensity, particularly in the carious portions, was found to be the only significant effect. This resulted in a slight improvement in the accuracy of the reconstructed doses.     

Thermal induced EPR signals in tooth enamel

Electron paramagnetic resonance (EPR) spectroscopy was used to detect the effects of temperature on powdered human tooth enamel, not irradiated in the laboratory. Samples were heated at temperature between 350 and 450, at 600 and at 1000°C, for different heating times, between 6 min and 39 h. Changes in the EPR spectra were detected, with the formation of new signals. Possible correlation between the changes in EPR spectra and modifications in the enamel and in the mineral phase of bone detected with other techniques is discussed. The implications for dosimetric applications of signals induced by overheating due to mechanical friction during sample preparation are underlined.     

Egyptian limestone for gamma dosimetry: an electron paramagnetic resonance study

The electron paramagnetic resonance (EPR) properties of limestone from a certain Egyptian site were investigated in order to propose an efficient and low-cost gamma dosimeter. Radiation-induced free radicals were of one type which was produced in the limestone samples at g=2.0066 after exposure to gamma radiation (⁶⁰Co). EPR spectrum was recorded and analyzed. The microwave power saturation curve and the effect of changing modulation amplitude on peak-to- peak signal height were investigated. The response of limestone to different radiation doses (0.5–20 kGy) was studied. Except for the decrease in signal intensities during the first five hours following irradiation, over the period of two months fair stabilities of signal intensities were noticed. From the current results, it is possible to conclude that natural limestone may be a suitable material for radiation dosimetry in the range of irradiation processing.     

Radiation dose reconstruction from L-band in vivo EPR spectroscopy of intact teeth: Comparison of methods

In vivo EPR tooth dosimetry is a more challenging problem than in vitro EPR dosimetry because of several potential additional sources of variation associated with measurements that are made in the mouth of a living subject. For in vivo measurement a lower RF frequency is used and, unlike in the in vitro studies, the tooth cannot be processed to optimize the amount and configuration of the enamel that is measured. Additional factors involved with in vivo measurements include the reproducibility of positioning the resonator on the surface of the tooth in the mouth, irregular tooth geometry, and the possible influence of environmental noise. Consequently, in addition to using the theoretical and empirical models developed for analyzing data from measurements of teeth in vitro, other unconventional and more robust methods of dose reconstruction may be needed. The experimental parameter of interest is the peak-to-peak amplitude of the spectrum, which is correlated to the radiation dose through a calibration curve to derive the reconstructed dose. In this study we describe and compare the results from seven types of computations to measure the peak-to-peak amplitude for estimation of the radiation induced signal. The data utilized were from three sets of in vivo measurements of irradiated teeth. Six different teeth with different doses were placed in the mouth of a volunteer in situ and measurements of each tooth were carried out on three different days. The standard error of dose prediction (SEP) is used as a figure of merit for quantifying precision of the reconstruction. We found that many of the methods gave fairly similar results, with the best error of prediction resulting from a computation based on a Lorentzian line model whose center field corresponds to the known parameter of the radiation-induced EPR spectra of teeth, with corrections from a standard sample that was measured as part of the data acquisition scheme. When the results from the three days of measurement were pooled, the SEP decreased dramatically, which suggests that one of the principal sources of variation in the data is the ability to precisely standardize the measurements conditions within the mouth. There are very plausible ways to accomplish improvements in the existing procedures.     

EPR dosimetry sensitivity enhancement by detection of rapid passage signal of the tooth enamel at low temperature

The four-fold improvement of EPR signal-to-noise ratio for radiation-induced paramagnetic centres in comparison with a conventional way is achieved by detection of the tooth enamel EPR signal at 77 K and rapid passage conditions.     

Pulsed Electron Spin Resonance Ex Situ Probe for Tooth Biodosimetry

An electron spin resonance (ESR) probe that includes a static field source and a microwave resonator for the measurement of paramagnetic defects in tooth enamel is presented. Such defects are known to be a good marker for quantifying the amount of ionizing radiation dose absorbed in the tooth. The probe can measure the tooth when it is positioned just above its outer surface, i.e., in ex situ geometry. It is operated in pulsed mode at a frequency of ~6.2 GHz that corresponds to the magnitude of the static magnetic field of its permanent magnet. A detailed design of the probe is provided, together with its specifications in terms of measurement volume and signal-to-noise-ratio for a typical sample. Experimental results that verify its sensitivity and capability to measure gamma-irradiated teeth are provided. The current minimal detected signal by the probe corresponds to a radiation dose of ~4 Gy.     

Formation of nanodefects in LiF crystals under gamma irradiation

The absorption spectra, photoluminescence spectra, and microhardness of LiF crystals exposed to gamma radiation from a shutdown reactor and a ⁶⁰Co source at a dose rate of 7.65 Gy/s are investigated. The structure of these crystals is determined using x-ray diffraction analysis. It is revealed that the Li sublattice contains not only point and complex radiation-induced defects but also 28-nm LiOH particles induced by gamma radiation. It is shown that the formation of defects occurs more efficiently upon exposure to radiation from a shutdown reactor than from a ⁶⁰Co source.     

Radiation Dosimetry Using Alanine and Electron Paramagnetic Resonance (EPR) Spectroscopy: A New Look at an Old Topic

The detection and quantification by electron paramagnetic resonance (EPR) spectroscopy of stable radicals formed in alanine by exposure to γ-radiation is used as a secondary standard for radiation dosimetry measurements, even though the EPR signal is actually derived from >1 radical with different spectral properties. For high radiation doses, microwave power saturation and spectral linewidths are both dependent on the received dose, and result in non-linear calibration curves. Furthermore, using a high-sensitivity microwave cavity, the power at which EPR signal saturation commences is ~0.3–0.4 mW for samples with irradiation doses ≤10 kGy; these values are an order of magnitude lower than those normally used in alanine dosimetry. In addition, the central peak of the first derivative spectrum, the height of which is commonly used in dosimetry measurements, is the most susceptible to microwave power saturation. Therefore, for high-level dosimetry we now recommend that analyses be performed under non-saturating conditions, and that the spectral acquisition parameters should be determined with a standard irradiated to ≤10 kGy to eliminate any intensity problems associated with variable saturation characteristics. At low radiation doses, variations in spectral saturation characteristics are negligible, and partially saturating conditions along with modulation amplitudes much higher than those normally used can reliably produce improved signal-to-noise ratios and allow extension of the methodology to practical working limits of ~0.1–0.2 Gy.     

Multi-frequency EPR study of radiation-induced radicals in tooth enamel

Human tooth enamel powders, unheated as well as heated prior to X -irradiation at room temperature, have been investigated by means of Q - and W -band Electron Paramagnetic Resonance (EPR). Upon irradiation of enamel, carbonate-derived radicals are generated. The simplest acquired EPR spectra in this study consist mainly of a group of three different \hbox{CO}_3^{3-} signals, with a very weak \hbox{CO}_2^{-} contribution. The characterisation of the paramagnetic species in enamel is quite important for the reliability of EPR applications ( e.g. , EPR retrospective dosimetry). The spectra from the heated samples reveal a striking resemblance with spectra from certain irradiated synthetic apatite powders. The spin Hamiltonian parameters obtained from the computer simulations of the Q - and W -band spectra are compared with those reported in the literature.     

In Vivo EPR For Dosimetry

As a result of terrorism, accident, or war, populations potentially can be exposed to doses of ionizing radiation that could cause direct clinical effects within days or weeks. There is a critical need to determine the magnitude of the exposure to individuals so that those with significant risk have appropriate procedures initiated immediately, while those without a significant probability of acute effects can be reassured and removed from the need for further consideration in the medical/emergency system. In many of the plausible scenarios there is an urgent need to make the determination very soon after the event and while the subject is still present. In vivo EPR measurements of radiation-induced changes in the enamel of teeth is a method, perhaps the only such method, which can differentiate among doses sufficiently for classifying individuals into categories for treatment with sufficient accuracy to facilitate decisions on medical treatment. In its current state, the in vivo EPR dosimeter can provide estimates of absorbed dose with an error approximately +/- 50 cGy over the range of interest for acute biological effects of radiation, assuming repeated measurements of the tooth in the mouth of the subject. The time required for acquisition, the lower limit, and the precision are expected to improve, with improvements in the resonator and the algorithm for acquiring and calculating the dose. The magnet system that is currently used, while potentially deployable, is somewhat large and heavy, requiring that it be mounted on a small truck or trailer. Several smaller magnets, including an intraoral magnet are under development, which would extend the ease of use of this technique.