ABSTRACT
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).
Subject(s)
Cobalt Radioisotopes , Dental Enamel/radiation effects , Gamma Rays , Dental Enamel/anatomy & histology , Dose-Response Relationship, Radiation , Electron Spin Resonance Spectroscopy/methods , Humans , In Vitro Techniques , Molar, ThirdABSTRACT
Intercomparison of EPR-dosimetric techniques using tooth enamel had been performed in order to check whether the results produced by different laboratories are consistent and accurate. Participants were supposed to evaluate doses applied to pulverized enamel samples, using routine techniques from their laboratories. The intercomparison has demonstrated a great variety of methods used for dose reconstruction. Peculiarities of experimental approaches are discussed systematically in terms of procedure for recording the EPR-spectra, determination of the amplitude of the radiation induced signal, determination of the dose, and error propagation.
Subject(s)
Dental Enamel/radiation effects , Electron Spin Resonance Spectroscopy/methods , Radiometry/methods , Dental Enamel/chemistry , Electron Spin Resonance Spectroscopy/statistics & numerical data , Evaluation Studies as Topic , Free Radicals/analysis , Free Radicals/radiation effects , Humans , Laboratories , Radiation Tolerance , Radiometry/statistics & numerical dataABSTRACT
Paramagnetic centres are present in human tooth enamel after irradiation with ultraviolet light. Their thermal stability and electron spin resonance spectrum coincide with those of the ion radicals created with gamma-rays are used in geological or archaeological dating and accident dosimetry. The long wavelength tail of their creation spectrum intersects with the short wavelength tail of the solar spectrum reaching Earth's surface, thus raising the question about the possible effect of solar irradiation on dating and dosimetry.
Subject(s)
Dental Enamel/chemistry , Dental Enamel/radiation effects , Ultraviolet Rays , Dentin/chemistry , Dentin/radiation effects , Electron Spin Resonance Spectroscopy , Free Radicals/analysis , HumansABSTRACT
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.
