Multi-point gamma-ray monitoring at radioprotection levels with image devices

Abstract

A multi-point system for the simultaneous interrogation of several extrinsic polymer optical fiber-based gamma-ray sensors is demonstrated. As a proof of concept, four different sensing heads have been measured, all of them based on a chemically etched fiber tip plus an inorganic scintillator powder. Two inorganic scintillators have been tested, namely Terbium doped Gadolinium Oxysulfide (Tb:GADOX) and Cerium doped Yttrium-Aluminum garnet (YAG:Ce). These sensing heads are interrogated with a commercial image device (CMOS camera). Such device does not need any cooling stage, optical filters or image intensifier elements. The response for each individual transducer is inside a 2D grid-shape array image, which provides a multiplexing method scalable with the number of the desired interrogation points. The interrogation procedure takes advantage of well-stablished digital image processing techniques, which include the selection of the regions of interest (ROIs) associated to the response of each individual sensing-head, plus the suitable RGB channel selection to improve the signal to noise ratio in the final measurement. Thus, only the Green channel has been found to render useful signal for gamma ray monitoring. Furthermore, the selection of the exposure time in the CMOS camera also permits to adjust the radiation levels to be detected.All tests were run under gamma irradiation from a calibrated 137Cs source, the reference isotope for environmental protection. The obtained results show the feasibility of simultaneously interrogating several gamma ray sensors, which can provide reliable measurements to quickly detect the presence of hazardous radioactive materials in large accidental leakage scenarios.