Yordanka Karakirova

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

Abstract 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.

Some Recent Developments of EPR Dosimetry

In the last three decades EPR spectrometry has expanded significantly in the field of practical applications. This is mainly due to its high sensitivity (1012–1013 molecules, which means 10–11 to 10–12 M) and selectivity (it can discover “needle in hayrick”). Moreover, it is a non-destructive technique and in some cases samples may be kept as documents for future inspection. The aim of the present chapter is to highlight the current status, as well as the near future trends in development of Solid State /EPR dosimetry. The main subjects considered are the recent developments in SS/EPR dosimetry in standard and emergency accidental cases, identification of irradiated foodstuffs as well as new approaches to the extension of the period of identification by EPR.

Heavy-ion-induced sucrose radicals investigated using EPR and UV spectroscopy.

The potential use of a sucrose dosimeter for estimating both linear energy transfer (LET) and the absorbed dose of heavy ion and X-ray radiation was investigated. The stable free radicals were produced when sucrose was irradiated with heavy ions, such as helium, carbon, silicon and neon ions, and when the X-ray radiation was similar to the obtained electron paramagnetic resonance (EPR) spectra, which were ∼7 mT wide and composed of several hyperfine structures. In addition, the total spin concentration resulting from heavy-ion irradiation increased linearly as the absorbed dose increased, and decreased logarithmically as the LET increased. These empirical relations imply that the LET at a certain dose can be determined from the spin concentration. For sucrose and alanine, both cross-sections following C-ion irradiation with a 50 Gy dose were ∼1.3 × 10(-12) [μm(2)], taking into account the molecular size of the samples. The values of these cross-sections imply that multiple ionizing particles were involved in the production of stable radicals. Furthermore, UV absorbance at 267 nm of an aqueous solution of irradiated sucrose was found to linearly increase with increasing absorbed dose. Therefore, the EPR and UV results suggest that sucrose can be a useful dosimeter for heavy-ion irradiation.