Eletrômetro para uso em metrologia de radiação ionizante

Abstract

Dosimeters perform an essential role in ionizing radiation applications. Its operation depends on the proportionality between the radiation dose rate and the current induced by ionizing radiation in a sensor element. Thus, it is possible to calculate the absorbed radiation dose by integrating the measured current over time. This work’s main objective was to develop an electronic circuit based on a transimpedance amplifier to work with currents of pico amperes generated by an ionization chamber exposed to radioactive sources. The first stage is the transimpedance amplifier, and a follower amplifier (for guarding circuit). The following stage is a summing amplifier, to allow zero and total gain adjustment, and, finally, a Butterworth filter, with the important role of filtering the 60 Hz frequency and adding a small gain to the circuit. The Butterworth filter output is sent to the STM32F103C8T6 microcontroller that manages the values read from the ADC port, buttons, and display for the user interface. The developed prototype can operate with currents from ±10 pA to ±1000 pA and generate polarization voltages for the ionization chamber in the range between ±100 V and ±400 V. It was assembled in a cabinet with a dedicated display and buttons. On the display, all necessary information is presented simultaneously. Tests were conducted to evaluate the effectiveness of the electronic filters used, repeatability (≤ 0,2%), stabilization time (≤ 0,05%), and linearity (R2 = 0.9993 for current and R2 = 0.9995 for accumulated charge), indicating the viability of the low-cost methodology proposed in this work for ionizing radiation dosimetry.