Feasibility study of a current mode gamma radiation dosimeter based on a commercial pin photodiode and a custom made auto-ranging electrometer

Abstract

An experimental study has been conducted to evaluate the feasibility of a current mode gamma radiation dosimeter, consisting of a commercial PIN photodiode as a radiation sensor, and a custom made auto-ranging electrometer for real-time measurement of the PIN photodiode?s response under radiation exposure. The radiation induced direct current response for single PIN photodiodes with different active areas, as well as for multiple PIN photodiodes connected in parallel, has been investigated. Three types of commercial silicon PIN photodiodes have been chosen for evaluation - S1223, BPW34, and PS100-6-CER2 PIN. During the experiment, five samples have been tested - three samples made of single PIN photodiodes (one sample of each photodiode type) and two samples formed by connecting multiple photodiodes in parallel (two BPW34 photodiodes in parallel and four BPW34 photodiodes in parallel). The samples have been irradiated with a 60Co gamma ray source and the relations between the induced photocurrent and the dose rate, and between the accumulated charge and the absorbed dose, have been determined. For measuring the photodiodes response, a custom made auto-ranging electrometer controlled by a personal computer, and capable of measuring direct currents from 50 pA to 10 mA with relative error less than 2.5%, has been used. Obtained results have shown very good linearity between the dose rate and the induced photocurrent for dose rates ranging from 0.93 Gy/h to 67 Gy/h. Also, very good linearity has been observed between the accumulated charge and the absorbed dose for all tested samples, within the investigated range of absorbed doses from 472 mGy to 3.3 Gy. On the basis of the obtained results, a simple model has been derived, enabling the estimation of the photodiode?s current response as a function of the dose rate and the photodiode?s geometry (active area and depletion layer width).