engleski

Relaxation mechanism of the first stable paramagnetic center in gamma-irradiated alanine; Application on ESR/Alanine Dosimetry

ESR and alanine have been successfully employed to detect irradiation dose. In the vicinity of therapy level doses (0.5-100 Gy) the intensity of detected signal is low and an additional possibility to improve signal/noise ratio implicates better sensitivity in the region of low doses. Indeed, it was shown that detection of stable paramagnetic centers in the gamma-irradiated L-alanine in the vicinity of 200 K yields around 30% larger signal than detection at room temperature for optimally tuned X-band ESR. The increase of signal was related to the extremal behaviour of relaxation rate due to fast motional dynamics of methyl group of stable L-alanine centres. It was suggested that electron proton cross-relaxation mechanism is involved in this relaxation rates. However, in the recent detail investigation of rotation correlation time of methyl groups the maximum contribution to the relaxation rate is expected at around 250 K for this relaxation mechanism. The relaxation mechanism responsible for maximum relaxation rate at 200 K has been investigated in this work. The temperature dependence of Transfer Saturation ESR Spectra, and transversal and longitudinal relaxation rates obtained by pulse ESR were studied. The complex temperature behaviours of relaxation rates are observed in the presence of strong spectral diffusion. The relaxation rates measured in the vide temperature range (5-280 K) are presented with corresponding relaxation mechanisms.

ESR; L-alanine; relaxation mechanisms

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