Study of the influence of grain size on the ESR angular response in alanine radicals

The simulation of electron paramagnetic resonance (EPR) spectra of radicals potentially due to alanine radiolysis has been done. Combining theoretical spectra in varying proportions allows computing different alanine spectra. The small changes in specific regions of experimental spectra correspond to weak variations in the proportion of radicals.As the study of several parameters, such as ESR angular response of powder or time after irradiation, is not possible in simulated spectra, experimental analyses have been carried out for the ESR angular response dependence on grain size in various combinations, corresponding to an available external surface. The stabilization of the angular response is associated with a spatial reorganization of radicals. It seems that available surface and radical proportions are linked. Predicted values of angular response calculated from pure powders do not correspond to experimental ones. Weak changes in spectra seem to confirm that these variations may be interpreted as a transformation of one radical into another.