Determination of the number of radiation induced alanine radicals by measuring the magnetic moment using SQUID magnetometer

Abstract

This study proposes a technique for alanine dosimetry using a superconducting quantum interference device (SQUID) magnetometer. Conventional measurements performed using an electron spin resonance spectrometer typically detect the relative amount of stable radicals generated in irradiated alanine using a magnetic field and microwaves. The SQUID magnetometer uses a magnetic field and a pickup coil to measure the total magnetic moment of stable alanine radicals. In this study, we demonstrate the principle of the alanine/SQUID measurement system. SQUID successfully detected the alanine radical at 4.2 K, and the reproducibility test showed that the relative standard deviation were 0.13 % and 0.10 % at the minimum value and averaged value in the measurement with different angles after 11 repetitions. This study shows that calibration curves can be constructed between 0.3 and 101 kGy and that the magnetic moment of alanine radicals can be measured in that dose range. The magnetic moments corresponding to the dose range of the calibration curve were 6.7×10−3 to 1.1×10−1μA⋅m2⋅mg−1. The number of radicals in alanine pellet induced by 101 kGy irradiation was 1.91×1022kg−1, which was determined by measuring the magnetic moment in the range of 80 K–300 K. Radiation chemical yield (G-value) of the alanine derived from the measured radical number was 0.31 μmol⋅J−1.