Development of a compact electron spin resonance system for measuring ESR signals of irradiated fingernails

The aims of this study were to develop and improve the sensitivity of an electron spin resonance (ESR) spectrometer and to demonstrate its functionality for dosimetry in measuring ESR signals from radiation-exposed fingernails. The newly-developed spectrometer was a lightweight (22 kg) one-box ESR device with a resonator showing a Q-factor higher than that of a previous Keycom model, which is quieter, without influence from magnetic modulation, and contains a fingernail positioner. The authors obtained the best measurement result after the cavity Q-factor was increased to more than 7,200 by continuous polishing of the inner surface of the cavity using deerskin. The common mode noise of "magic T" was also successfully decreased to as low as one-half by completely tuning the arm balance. Moreover, the flatness of the modulated magnetic field was increased by as much as two-fold by changing the coil conformation. These efforts markedly decreased the noise level and extended downwardly the linear portion of dose dependence.