Development of the Theoretical Relationship between the Electron Paramagnetic Resonance (EPR) Intensity and Absorbed Dose by Alanine

The purpose of the present study is the development of a theoretical relationship between the Electron Paramagnetic Resonance (EPR) intensity and the levels of absorbed dose in Alanine based on the average energy of the radical production. To this end, in the first phase of the present study, the EPR intensity vs. Alanine radical population was simulated based on the quantum mechanics perturbation theory using the Easyspin code. In the second phase, the EPR intensity vs. the levels of absorbed dose in Alanine was measured in an experimental setting. In the EPR dosimetry method, the EPR intensity is obtained from a reference sample with a specified dose, and for an unknown sample, the dose is calculated through measuring the EPR intensity and then comparing it to the reference sample. Previous studies showed that the relationship between the EPR intensity and the absorbed dose is not linear, therefore, for dosimetry purposes, it is better to use the EPR intensity conversion factor in terms of the absorbed dose (calibration curve). The purpose of this study is to define this calibration curve. To this end, a relationship between the EPR intensity and the absorbed dose based on empirical measurement was established. the experimental measurements conducted by the EPR machine were employed to validate the effectiveness/accuracy of the proposed solution.Comparison of the signal intensity vs. absorbed doses in the simulation and the experimental studies showed a very close agreement at the low doses but at the high energy doses there is no linear relationship between them. Therefore, the growth of the population vs. the absorbed doses is not linear. In other word, the average energy of the radical production cannot be supposed constant. Therefore, a non-linear calibration equation was developed to link the EPR intensities with the radical populations and/or absorbed dose in Alanine. The simulation and experimental studies demonstrated the effectiveness of the proposed calibration equation at high-energy gamma radiation.