Resonance Dosimetry Research Articles

A new ESR dosimeter based on polytetrafluoroethylene

A new electron spin resonance (ESR) dosimetry system based on the ESR response of polytetrafluoroethylene is presented. The dose response of these dosimeters irradiated with 60Co gamma radiation was linear in the range from 6 x 10(2) up to 1.5 x 10(5) Gy, having a repeatability of +/-1% and a high degree of reliability (Cf = 1.054). The persistence of the signal was monitored over a period of one month. ESR signal decay was 5-7% in the temperature range from room temperature up to 40 degrees C.

Electron spin resonance dosimetry of teeth of Goiânia radiation accident victims

Electron spin resonance (ESR) spectroscopy is used to assess absorbed doses of six teeth belonging to victims of the highly irradiated group of Goiânia accident. The influence of the broad background signal at g = 2.0040 as well as of the unstable fraction of CO2- radicals was taken into account in dose estimates. Three victims teeth showed absorbed doses comparable to those estimated by chromosomal analysis. For the other three teeth, the doses were higher by a factor of 1.3, 1.8 and 2.2.

Cavity theory applied to the dosimetry of systemic radiotherapy of bone metastases

A two-component model of an osteoblastic metastatic lesion has been developed to determine the absorbed dose delivered to soft tissue during systemic radiotherapy of osseous metastases. Doses to soft tissue from radioisotopes distributed in bone were calculated using Burlin's general cavity theory. A correction term was used to account for the absence of charged particle equilibrium within the metastatic lesion. Radiation doses for 153Sm, 186Re, 89Sr and 32P were calculated for several physiologically realistic lesion structures. Burlin's cavity weighting factor was greatest for higher energy isotopes and it decreased as the soft tissue cavity size increased. The correction for the absence of charged particle equilibrium also decreased with soft tissue pathlength, but increased with average bone pathlengths. Doses to soft tissue cavities ranged from 0.1 to 0.2 Gy MBq-1 d-1 for 153Sm to 0.5 to 0.6 Gy MBq-1 d-1 for 32P. Using the factors calculated in this work, the dose to soft tissue cavities within bone metastases can be calculated when the dose to adjacent bone has been determined, perhaps by autoradiography or electron paramagnetic resonance dosimetry. The doses calculated with this more accurate model of bone metastases demonstrate errors of 20% to 50% in previous calculations of the average dose to homogeneous metastatic lesions.

Thesis Abstract: Electron paramagnetic resonance dosimetry: methodology and material characterization

Thesis Abstract: Electron paramagnetic resonance dosimetry: methodology and material characterization

ESR Solid State Dosimetry: Behaviour of Various Amino Acids and Blend Preparation Procedures

In several laboratories all around the world, electron spin resonance (ESR) dosimetry is a well-established reference dosimetric system in industrial applications of ionising radiation, and its use is also proposed in radiation therapy and accident dosimetry. In the present experimental investigation preparation procedures of alanine-polyethylene solid state dosemeters (SSD) with optimised characteristics were defined, both modifying the commonly used blend composition and preparation, and choosing the best ESR spectra recording conditions, some other amino acids that could be alternatives to alanine in obtaining ESR dosemeters with better performances than alanine ones were also tested. Results obtained up to now (the research is still under way) confirm that alanine seems to be the most suitable material for ESR dosimetry. Methods to improve reproducibility are also discussed.

An EPR dosimetry method for rapid scanning of children following a radiation accident using deciduous teeth.

Electron paramagnetic resonance dosimetry may be applied to whole deciduous teeth of children. This makes it feasible to make direct measurement of absorbed gamma ray dose in the days and weeks following a nuclear accident, particularly if used in conjunction with a public awareness program. The technique reported here requires little sample preparation and has resulted in precision of approximately 30 mGy (1 sigma) for a deciduous incisor. Under conditions for rapid screening procedures, the methodology is estimated to provide 0.5 Gy accuracy. The largest error in the process is the determination of an appropriate background native signal for subtraction from the whole tooth spectrum. The native signal is superimposed on the radiation-induced signal, and the subtraction requires knowledge of a sample's relative content of enamel and dentin along with their relative native signal intensities. Using a composite background standard, an equivalent absorbed dose of 70+/-38 mGy (1 sigma) was determined. The lower detection limit of the technique was achieved by the elimination of anisotropic effects through rotation of the sample during measurement, together with subtraction of the standard native background signal and empty tube background spectra from the sample spectra.

A close correlation between electron spin resonance (ESR) dosimetry from tooth enamel and cytogenetic dosimetry from lymphocytes of Hiroshima atomic-bomb survivors

Purpose: To estimate gamma -ray doses received by Hiroshima atomic bomb survivors using electron spin resonance (ESR) of tooth enamel and to compare the results with cytogenetic data. Materials and methods: Tooth enamel ESR was performed for 100 teeth donated from 69 Hiroshima survivors, and conventional cytogenetic examinations were conducted for 61 of the tooth donors. To evaluate possible contamination from dental X-ray exposure, which primarily affects the tooth's buccal surface, each tooth was divided into buccal and lingual parts for subsequent independent enamel isolation and ESR measurement. Results: Almost 20 teeth showed considerably larger buccal doses than lingual doses, but most of these discrepant teeth were incisors and canines. The results are probably attributable to solar light exposure. In contrast, the buccal and lingual doses found in molars were similar. Conventional translocation data of lymphocytes and ESR-estimated doses of 40 donors of molars showed the dose-response for translocations to be almost the same as that expected from in vitro gamma -ray irradiation experiments. Conclusions: Both tooth enamel ESR and lymphocyte cytogenetics are useful measures for individual biodosimetry of acute radiation exposure, even half a century after the exposure occurred.

A mathematical approach to optimal selection of dose values in the additive dose method of EPR dosimetry

Additive dose methods commonly used in electron paramagnetic resonance (EPR) dosimetry are time consuming and labor intensive. We have developed a mathematical approach for determining optimal spacing of applied doses and the number of spectra which should be taken at each dose level. Expected uncertainties in the data points are assumed to be normally distributed with a fixed standard deviation and the linearity of the dose response is also assumed. The optimum spacing and number of points necessary for minimal error can be estimated as can the likely error in the resulting dose estimate. When low doses are being estimated for enamel samples, the optimal spacing is shown to be a concentration of points near the zero dose value with fewer spectra taken at a single high dose value within the range of known linearity. Optimization of the analytical process results in increased accuracy and sample throughput.

Alkaline denaturation of dentin--A simple way to isolate human tooth enamel for electron spin resonance dosimetry.

Electron spin resonance (ESR) of tooth enamel is a recently developed method for the retrospective dose estimation of human radiation exposures. The assay requires isolation of enamel from dentin, which is difficult because the boundary between enamel and dentin is not easily discernible. Here we describe a simple method for isolating enamel by alkaline denaturation of dentin. The method requires 4 weeks, but scratching of the denatured and hence softened dentin is needed only once a week. Above all, no special skill is required. We found that the alkaline treatment did not cause deterioration of the ESR signal recorded in enamel exposed to 2 Gy of gamma rays prior to its isolation. The assay is particularly suited for teeth containing many cracks that were generated during long-term storage after extraction of the teeth. Such teeth tend to disintegrate during enamel isolation processes, which poses difficulties to isolate enamel mechanically from individual small pieces.

Pilot study of the Urals population by tooth electron paramagnetic resonance dosimetry.

During 1949-1956, about 76 x 10(6)m3 of radioactive liquid waste containing a total activity of 10(17) Bq was discharged into the Techa River by the first Russian industrial nuclear facility Mayak. As a consequence, the population living in the river valley received considerable internal and external radiation doses. The results of a first application of electron paramagnetic resonance (EPR) of tooth enamel for a retrospective individual dose evaluation of the residents of the Techa riverside are presented. Three main contributions to the dose absorbed in tooth enamel have been considered: external exposure mainly from the Techa River sediments, internal exposure mainly due to 90Sr; and background radiation including all other sources of exposure except the Techa River. The teeth of 86 inhabitants of the town Kamensk-Uralskii were analysed to determine the age-dependent contribution of the background radiation to the enamel dose. For 22 residents of the middle and lower Techa riverside, measurements of the 90Sr whole-body content and EPR measurements of the absorbed dose in enamel were used to establish a correlation between these two quantities. Finally, absorbed doses in the enamel of five residents of the upper Techa riverside were determined by EPR method. Contributions of the background radiation and the internal 90Sr contamination were subtracted to determine the external exposure of the residents.

142 EPR/alanine dosimetry: Just another dose measuring system?

Electron paramagnetic resonance (EPR) dosimetry is based on a non-destructive quantitative measurement of stable free radicals in samples, induced by energy deposited by radiation. The amino acid L- α alanine shows favorable dosimetric properties: a linear response with dose, no energy nor dose rate dependence and no fading. The detector itself is small in size and tissue equivalent, which makes it an ideal measuring device for radiotherapy. Commercial available alanine dosimeters together with a low budget desktop spectrometer (Bruker EMS 104) are tested since more than two years at our department as an in vivo dose measuring system. All types of dosimeters show a perfect linear dose-response, but the background level (zero dose signal) can differ significantly between different manufacturers: from 2.5 Gy to 14 Gy. Measurement precision is less than 1% (1 σ ) if dose exceeds 10 Gy. No fading was observed over a period of one year. The reliability of alanine dosimetry for in vivo dosimetry will be illustrated with several case studies: dose measurements at the cervix wall during treatment of the cervix carcinoma with high and low dose rate brachytherapy, dose to the rectum wall; entry dose measurements during teletherapy. For all these very different cases correspondence of calculated and measured dose was excellent. From our experience we believe that alanine dosimetry can play an important role in clinical dosimetry in the future, combining advantages from TLD and diode dosimetry systems.

Research and development activities in electron paramagnetic resonance dosimetry

This work describes ongoing activities in Electron Paramagnetic Resonance (EPR) dosimetry at the National Institute of Standards and Technology. Progress in the commercialization of the alanine-EPR system will be discussed along with basic research in high-dose dosimetry, including EPR imaging.

Temperature and frequency effects in tooth enamel electron spin resonance dosimetry

Electron spin resonance of CO3(3-) molecule ions in human tooth enamel have been studied at various temperatures between 4 and 350 K and at various microwave powers in the 9 GHz (X) band. Signal saturation during cooling due to slowing down of the electron spin relaxation has been established. The 35 GHz (Q) band spectra of tooth enamel, irradiated with various gamma-ray doses, are also presented. Q band ESR dosimetry offers some advantages over the X-band dosimetry due to signal enhancement from the spin level population difference and especially due to a better filling factor which is important when only minute quantities (a few mg) of enamel are available.

The Use of Sugar Pellets in ESR Dosimetry

Table sugar (sucrose) is a convenient, common, tissue-equivalent material suitable for electron spin resonance (ESR) dosimetry of ionising radiation. The simple free radical signal in irradiated sugar is stabilised if the sugar is made into pellets using an inert silicone elastomer (Dow Corning 732). Such pellets, which offer greater convenience and signal stability and reproducibility, have been prepared and tested for their radiation response, sensitivity and post-irradiation stability. Irradiated sugar is detectable at ≥0.1 Gy, the signal intensity is linear with dose, and the fading of the signal, post-irradiation, is minimal for samples kept under ambient conditions

From earth to space: ESR dosimetry moves toward the 21st century

Abstract Future developments of electron spin resonance (ESR) dosimetry, dating and imaging (microscopy) are discussed following a brief review of the present state of the art. The Third International Symposium on ESR Dosimetry and Applications in 1991 gives on opportunity for an outline of further developments of the methods as we move toward 21st century. One direction these developments need to take is toward space sciences where ESR dosimetry of solar wind, particulate radiation as well as dating of planetary and interplanetary substances like comets and asteroids must be studied first in the laboratory. Physics on defects in solid H 2 O, CO 2 and CH 4 abundant in outer space must be studied. Improvement of the alanine dosimeters and monitoring irradiated foods and the in-vivo human tooth dosimeter for accident dosimetry are essential in the development of ESR dosimetry. ESR ages of geological substances must be refined on a firm physical basis by establishing models of defects whose signals are used for ESR dating. Finally, magnetic resonance imaging (MRI) both CT- and scanning ESR for spatial distribution of spins must be developed with the pulsed ESR method which can separate overlapping signals with different relaxation times. A small portable ESR will make this ESR metrology more practical in many fields. The sensitivity increase can be realized by cooling the oscillator and detector diode and electronics to reduce thermal noise.

Use of Alanine-Silicone Pellets for Electron Paramagnetic Resonance γ Dosimetry

Silicone is proposed as an alternative binding substance in the production of D-L alanine pellets used in electron paramagnetic resonance (EPR) dosimetry of gamma rays. The dosimeters are manufactured at room temperature, making the production simple. Examination by EPR silicone-alanine pellets irradiated with 60Co gamma rays in the dose range 10 to 10(6) Gy shows that the proposed silicone binder does not affect typical alanine dose-response curves. Thermal stability of the pellets below 40 degrees C is good, but their pre-dose EPR signal amplitude is slightly higher than for nonirradiated alanine.

An Electron Spin Resonance System for In-vivo Human Tooth Dosimetry

An electron spin resonance (ESR) dosimetry system for an in-vivo human tooth has been developed to measure, without extraction, the cumulative radiation dose in a tooth. The system consists of a TE102 cavity with an aperture at the end plate, a Nd–B–Fe (Neomax) oral magnet and a commercial ESR spectrometer. The front molar is attached to the aperture of the cavity to detect radicals created by radiation in the tooth enamel. Optimum dosimetry conditions were investigated using an extracted human tooth.

Electron spin resonance dosimetric properties of bone.

The characteristics of electron spin resonance (ESR) dosimetry using bovine bone samples are described. The number of paramagnetic centers created by gamma radiation in the inorganic bone matrix was measured as a function of absorbed dose. The minimum detectable dose was 0.5 Gy for 60Co gamma rays. The response was linear up to the maximum dose studied (30 Gy) and independent of dose rate up to the maximum dose rate used (1.67 Gy min-1). For different bone samples the reproducibility was 5%. This method may be valuable for nuclear accident dosimetry.