Design of wide energy range coded aperture mask of an environment radiation monitoring system

It is of significant importance to develop an environment radiation monitoring system since the tracking and management of radiation sources are becoming more and more important in many sectors such as nuclear power plants, hospitals, isotope production facilities, research laboratories and so on. In this paper, we designed a coded aperture mask used in an environment radiation monitoring system, which is able to locate gamma-ray sources in the environment as well as to do the spectrum analysis of them. We determine the parameters of the coded aperture system through existed coded aperture theories and Monte-Carlo simulation to achieve high sensitivity, large field of view (FOV), best image quality in a wide energy range, and also acceptable spatial resolution. We defined a new figure of merit (FoM) which is different from the conventional FoM to evaluate the quality of the reconstructed images of the Monte-Carlo simulation. Using the anti-symmetric mask pattern (i.e. the mask exchange the blocked and hole pixels in the mask upon a 90 degree rotation, except the pixel in the center), the system is able to overcome the unavoidable detector deficiency and also has the potential to be used in a near-field situation with little near-field artifact. According to preliminary simulations, the mask design could enable Cs-137 and Co-57 imaging at an excellent image quality.