Evaluation of 2-methylalanine and lithium formate monohydrate as alternative ESR dosimeters

<title>Abstract</title> <p>Electron spin or paramagnetic resonance (ESR or EPR) dosimetry is a reliable technique for radiation dose assessment based on the detection of radiation-induced stable radicals. L-alanine is a widely used material as an international reference for ESR dosimetry because of its tissue equivalence, excellent reproducibility, long-term signal stability, and linear dose response over a wide dose range of up to &gt; 100 kGy. However, the use of L-alanine for lower dose (&lt; 10 Gy) measurements is limited, although the health effects of radiation exposure are particulrly concerning in this dose range. An alternative material with enhanced sensitivity and similar favorable dosimetric properties should be developed. In this study, the ESR dosimetric characteristics of 2-methylalanine and lithium formate monohydrate were systematically evaluated and compared with those of L-alanine under identical irradiation and measurement conditions. The microwave saturation behavior differed among the three materials, with 2-methylalanine exhibiting the highest resistance to saturation, followed by lithium formate monohydrate, whereas L-alanine showed saturation at relatively lower microwave powers. Following X-ray irradiation in the dose range of 0–10 Gy, all three materials exhibited a dose-dependent increase in peak-to-peak ESR signal amplitude, demonstrating their suitability for quantitative dose evaluation. Among the investigated materials, 2-methylalanine showed the highest dose sensitivity, followed by lithium formate, whereas L-alanine exhibited the lowest response. The difference in ESR signal intensity between these materials became evident at absorbed doses above 2 Gy, where 2-methylalanine demonstrated a higher and more linear response than the other materials. All the materials maintained stable ESR signals during one week of storage. These results demonstrate that 2-methylalanine has the potential as an alternative ESR dosimeter that can adequately cover the radiologically concerned dose range.</p>