Design of a Low-Cost Auto-Ranging Electrometer for Current-Mode Dosimetry

This paper presents a low-cost auto-ranging electrometer for current-mode dosimetric applications. The proposed electrometer is based on a variable gain transimpedance amplifier, and has been realized with commercially available components. It can operate as a stand-alone unit with an integrated display for real-time measurement visualization, or can be interfaced to a personal computer (PC) over USB or RS-232 connections, allowing real-time visualization and data storage using custom-made PC application software. The electrometer is capable of measuring direct currents from 50 pA to 10 µA in three sensitivity ranges, with relative error less than 2.5%, and response time of approximately 0.2 s in each range. The performance of the proposed electrometer is comparable with custom-made electrometers reported in the literature, as well as with several standard commercial dosimetric electrometers. The electrometer has been validated experimentally for measuring the direct current of four commercial PIN photodiodes under gamma irradiation from a Co-60 source. The results have shown that the realized electrometer, combined with the investigated PIN photodiodes, can serve as a low-cost current-mode dosimeter for measuring the gamma radiation dose rates from 0.9 Gy/h to 34 Gy/h, and absorbed doses at least up to 33 Gy.