A study of characteristics of the formation of stable paramagnetic centers in alanine exposed to alpha radiation by electron paramagnetic resonance spectroscopy

The dependence of the spectral shape of alanine on a microwave power in the spectrometer resonator when irradiated by gamma rays and alpha particles was investigated. No significant differences between the spectra recorded at a microwave power of less than 5 mW were observed. On the contrary, for values of microwave power in the spectrometer resonator more than 10 mW there is a considerable variation in the shape of the spectrum of irradiated alanine with different types of radiation. It is shown that the difference in the shape of the spectra when irradiated by alpha particles and gamma rays is caused by increase in the radiation output of recorded radicals of the second and the third types which are formed after the isolation of hydrogen atom from a central carbon atom and after radiolysis due to separation of two protons and oxygen atoms from an alanine molecule, respectively. These types of radicals are also formed during heating alanine to 200 °C. Thus, the results indicate that under the exposure of alpha radiation the increased yield of the same radicals in alanine as upon heating is observed what can be explained by local heating effect in the tracks of alpha particles with a high linear energy transfer. The comparative yield of three different types of radicals responsible for the components of the total spectrum when irradiated with alpha particles and gamma rays was studied by deconvolution into the components of the total EPR spectrum of irradiated alanine. It was shown that the yield of radicals of the third type under alpha radiation is more than 20% whereas under gamma-irradiation the contribution does not exceed 10%. It was also shown that the output of the second type of radicals becomes dominant when the microwave power in the spectrometer resonator is over 20 mW during irradiation by gamma rays and 40 mW when irradiated by alpha particles.