engleski

Relaxation rates of stable paramagnetic centers in L-alanine detected by transfer saturation EPR

EPR spectra of irradiated l-alanine currently employed in alanine/EPR dosimetry exhibit a complex relaxation rate behavior. The stable l-alanine radical was examined by transfer saturation EPR (CW-TSEPR) in the temperature region of fast motion of the methyl group (180 K-320 K). From the obtained spectral line broadening and saturation factors of the spectral intensities it was demonstrated that relaxation rate strongly depends on spectral diffusion mechanism. The effect of such spectral diffusion on the accurate estimation of correlation time for the methyl rotation was discussed. The obtained CW-TSEPR spectra indicate that an additional correlation time with higher potential barrier, than the barrier of the methyl group of stable radical center, should be involved in the relaxation process. This additional correlation time can be assignment to the neighbor methyl groups of the radical centers. The obtained dynamical parameters have been compared with those previously obtained by proton nuclear magnetic resonance (NMR) on undamaged crystals.

alanine; dosimetry; ESR

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