A Portable Femtoampere-Sensitive Readout System for a High-Pressure Argon Ionization Chamber

This article presents the design, implementation, and validation of a portable femtoampere-sensitive electronic readout system for a high-pressure argon-filled ionization chamber (IC) radiation detector. The system integrates an ionization tube designed and fabricated at TENMAK laboratories as a part of this study together with a low-noise analog front-end, precision digital processing, and a power-efficient embedded platform. At its core is a transimpedance amplifier (TIA) based on an electrometer-grade op-amp (ADA4530-1), enabling accurate conversion of ionization currents in the femtoampere range. A dual-path amplification architecture ensures dynamic range adaptability across low- and high-dose-rate conditions. The digital subsystem - featuring a 16-bit sigma-delta analog-to-digital converter (ADC)-equipped STM32 microcontroller - handles real-time digitization, temperature compensation, and self-adjustment offset via integrated digital-to-analog converters (DACs). The device was calibrated and tested at the Secondary Standard Dosimetry Laboratory (SSDL) of Turkish Nuclear Energy Research Institute (TENMAK), covering a wide radiation range from 3~μ Sv/h to 60 mSv/h using multiple 137Cs sources. The system demonstrated excellent linearity (R2 > 0.998 ), with a minimum detectable dose rate of approximately 2~μ Sv/h, and maintained a total measurement error below 10%. These results affirm the device's suitability for portable, high-precision radiation monitoring in field and safety applications. The novelty of this work lies in the integration of a high-pressure argon IC with a dual-path femtoampere readout front-end and a fully self-adjusting digital control unit, enabling portable, low-dose-rate detection below 3 μ Sv/h.