N.D. Yordanov

Early-Stage Evolution of the EPR Spectrum of Crystalline Sucrose at Room Temperature after High-Dose X Irradiation

H. Vrielinck, H. De Cooman, Y. Karakirova, N.D. Yordanov, F. Callens
Radiation Research
172 (2), 226-233


X irradiation of sucrose single crystals at room temperature leads to the production of stable radicals, which give rise to the dosimetric electron paramagnetic resonance (EPR) signal. In the first few hours after irradiation, however, the shape of the EPR spectrum changes drastically. Based on two-dimensional field-frequency electron nuclear double resonance (FF-ENDOR) measurements, we demonstrate that, after high-dose (5 kGy) and high-dose-rate irradiation, several species with limited stability at room temperature are produced next to the stable radicals. For two of these species, the main characteristics could be determined. Analysis of the time evolution of the FF-ENDOR and room-temperature EPR spectra in the first few hours after irradiation leads to the conclusion that these meta-stable radicals mainly recombine into diamagnetic species, while transformation into stable radicals is at most a marginal process.

Radiation-induced defects in sucrose single crystals, revisited: A combined electron magnetic resonance and density functional theory study

H. De Cooman, E. Pauwels, H. Vrielinck, A. Dimitrova, N.D. Yordanov, E. Sagstuen, M. Waroquier, F. Callens
Spectrochimica Acta Part A (Mol. & biomol.)
69 (5), 1372-1383


The results are presented of an electron magnetic resonance analysis at 110 K of radiation-induced defects in sucrose single crystals X-irradiated at room temperature, yielding a total of nine 1H hyperfine coupling tensors assigned to three different radical species. Comparisons are made with results previously reported in the literature. By means of electron paramagnetic resonance and electron nuclear double resonance temperature variation scans, most of the discrepancies between the present 110 K study and a previous 295 K study by Sagstuen and co-workers are shown to originate from the temperature dependence of proton relaxation times and hyperfine coupling constants. Finally, radical models previously suggested in the literature are convincingly refuted by means of quantum chemical density functional theory calculations.

Dosimetric characteristics of different types of saccharides: An EPR and UV spectrometric study

Y. Karakirova, N.D. Yordanov, H. De Cooman, H. Vrielinck, F. Callens
Radiation Physics and Chemistry
79 (5), 654-659


The time stability and dose response of the free radicals produced in various types of “less-studied” mono- and disaccharides by γ-radiation is studied by EPR (Electron Paramagnetic Resonance) and UV spectrometry. The time evolution of the shape of the EPR spectra of irradiated saccharides is investigated from 5 min to 5 months after irradiation. The intensity of the stable EPR signal is studied as a function of the absorbed γ-dose in the range 0.5–20 kGy. Aqueous solutions of irradiated solid saccharides exhibit a UV absorption maximum in the range 250–290 nm. A linear dependency is found between the magnitude of the UV absorption maximum and the absorbed γ-dose. The time stability of the UV absorption maximum is also studied for every saccharide. The results are compared with those obtained for irradiated sucrose.

Tentative Models for Radiation-Induced Defects in Sucrose Single Crystals at Room Temperature: a Combined EMR and DFT study


Conference / event / venue 

10th International Workshop on Electron Magnetic Resonance Of Disordered Systems
Sofia, Bulgaria
Thursday, 7 June, 2007 to Thursday, 14 June, 2007
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