Applicability of the Dose Spiking Electron Paramagnetic Resonance Method for the Quantitative Measurements of Low Doses in Alanine Dosimetry

Ionizing radiation generates unpaired electrons or free radical centers in alanine. The electron paramagnetic resonance (EPR) detects, identifies, and quantifies these free radicals, proportional to the absorbed dose. The accurate measurements of low doses using EPR dosimetry with alanine are highly challenging due to (1) the weak EPR dosimetric signal from low dose alanine and measurement errors, (2) the sample anisotropy in crystalline alanine, and (3) the background signals from sample impurities. This study explores the feasibility of using the dose spiking EPR technique to overcome these challenges and decreases the detection limit up to 20 milligray (mGy) in a low dose measurement using EPR. The measurement errors from the sample anisotropy were reduced by rotating the samples relative to the constant magnetic field direction using a goniometer and averaging the resulting EPR spectra. This technique decreased the measurement errors at high doses; however, it was insufficient to decrease the detection limit and increase the measurement accuracy at low doses (<0.5 Gy). As a result, the high measurement accuracy at the high doses (>4 Gy) was exploited to increase the accuracy at the low doses using the dose spiking EPR technique. To this end, the low-dose alanine sample, undetectable and not reliably measurable in the X-band continuous wave (CW) EPR spectrometer, spikes with a high dose (4 Gy). Then, the total dose was measured and subtracted from a spike dose to get the initial low dose. This technique detected and measured the low doses with reliable accuracy (+/- 10%). As a result, we concluded that this method has great potential to solve the low dose measurement problems in alanine dosimetry.