X- and Q-band EPR study on dosimetric biomaterials

Electron paramagnetic resonance (EPR) spectroscopy (X- and Q-band) was used for identification of stable radicals in: compact bone powder, shell of arcidae mollusc and crystalline alanine. The aim of our investigation was to analyze the complex EPR spectra of these materials and to identify paramagnetic species contributing to it. The most successful results were obtained in the EPR study (X- and Q-band) on deproteinized and irradiated bone powder and arcidae shell at room temperature

EPR and ESEEM study of silver clusters in ZK-4 molecular sieves

Silver clusters generated by g-irradiation in ZK-4 zeolites – isostructural with Linde type A (LTA) zeolite, have been studied by electron paramagnetic resonance (EPR) spectroscopy. It was shown that even a small decrease of cation capacity resulting from a lower Si/Al ratio in the framework affects distinctly silver agglomeration. In dehydrated ZK-4 with Si/Al = 1.2 and 2.4 only silver dimers are stabilized, whereas in Linde 4A silver hexamers were trapped. In ZK-4 exposed to H2O and CH3OH, silver tetramers Ag43+ efficiently are formed. The results of electron spin echo envelope modulation (ESEEM) showed that the adsorbate molecules are in close vicinity to the clusters. It was postulated that in zeolites with low cation capacity the adsorbate molecules make difficult Ag0 migration promoting the reactions with Ag+ cations located in the same sodalite cage

EPR study of highly stable methyl radicals trapped in synthetic H-rho zeolite

Methyl radicals generated by ă-irradiation in the proton form of synthetic rho zeolite exposed to CH4 have been investigated by electron paramagnetic resonance (EPR) in the temperature range 110-370 K. Depending on the methane adsorption temperature two EPR spectra of oCH3 radicals were recorded. The isotropic quartet observed after CH4 adsorption at room temperature was assigned to oCH3 radicals freely rotating in the middle of octagonal prism. After adsorption at 413 K, the isotropic quartet is overlapped with the second signal characterized with anisotropy of hyperfine splitting and g-value. It is postulated that anisotropic signal represents the oCH3 radicals located in á-cages and strongly interacting with silicaalumina framework. The mechanisms of radiolytic formation of methyl radicals and the possible stabilization sites are also discussed

EPR study of γ-irradiated feather keratin and human fingernails concerning retrospective dose assessment

In this paper we report the results of comparative EPR studies on free radicals generated in γ-irradiated powder samples of feather keratin powder and human fingernails. In degassed samples of both materials irradiated at 77 K the major component of EPR spectrum represents sulphur-centred radicals in cysteine residues. It quickly decays after air admission at room temperature while a singlet assigned to semiquinone melanin radicals remains the only one seen. The singlet recorded with fingernails decays slowly at room temperature and might be potentially useful for dose assessment by EPR. The advantages and limitations of fingernails EPR dosimetry are discussed

EPR study on biominerals as materials for retrospective dosimetry

Stable paramagnetic species, induced by irradiation in biominerals, can be successfully used as an EPR dosimeter in numerous domains of scientific activity. In hydroxyapatite, the main mineral component of bones, the most stable signal is assigned to CO2 - ion radical. The signal is dose dependent and allows to determine the absorbed dose in a wide range till 20 kGy, with detection limit for tooth enamel below 1 Gy. The additive dose method was applied to EPR dating of archeological objects and EPR dosimetry after accidental overexposing during radiotherapy. It was found that the age of remains excavated from the “tomb of giants” belonging to Nuraghic culture developed in Sardinia island is about 3160 years old (1160 years BC). The dose obtained by patients during the accident at the Białystok Oncological Center was evaluated at about 75 Gy. Searching for potential dosimeters among other biominerals shows that mollusc shells have very promising properties. The lowest dose detection limit was found for an Arcidae shell. Both fresh water and sea mollusc shells are useful to be used for dosimetry in the low dose range

Multifrequency EPR study on radiation induced centers in calcium carbonates labeled with 13C

In calcite and aragonite, γ-irradiated at 77 K, several paramagnetic centers were generated and detected by EPR spectroscopy; in calcite, CO3 – (orthorhombic symmetry, bulk and bonded to surface), CO3 3–, NO3 2–, O3 –, and in aragonite CO2 – (isotropic and orthorhombic symmetry) depending on the type of calcium carbonate used. For calcium carbonates enriched with 13C more detailed information about the formed radicals was possible to be obtained. In both natural (white coral) and synthetic aragonite the same radicals were identifi ed with main differences in the properties of CO2 – radicals. An application of Q-band EPR allowed to avoid the signals overlap giving the characteristics of radical anisotropy