Low-cost radioactivity monitoring with scintillating fibers and silicon photomultipliers

ABSTRACT A new detector technology was developed, particularly suitable for low -cost radioactivity monitoring in radwaste storage sites. It consists of a scintillating optical fiber coupled at each end to a silicon photomultiplier (SiPM) . The single photon sensitivity of the SiPM, along with the left -right coincidence constraint, allows to achieve a reasonable sensitivity to gamma radiation even though using a thin 1mm diameter plastic scintillating fiber. Simulation results are in perfec t agreement with the measured behavior, and several implementations are under way. The possibility of choosing the fiber length and shape makes them very flexible both conceptually and mechanically. Any improvement in the SiPM development technology reflec ts immediately into an improvement in the detector performance. Keywords: Silicon Photomultiplier, SiPM, scintillating fiber, gamma detector, radiation detector, radioactive waste. 1. INTRODUCTION The term radioactive waste, or shortly radwaste, indicates waste containing radioactive material. It is usually produced as a residue of nuclear processes, such as nuclear fission, even though industrial processes and medical applications may also produce radioactive waste. Contrary to chemical waste dangerousnes s, radioactivity decreases with time, therefore one could in principle seal and isolate the waste for some time until its radioactivity poses no relevant risk. Unfortunately Osome timeO can range from a few hours to years for medical and industrial radwast e, and up to tens of thousands of years for high -level waste from nuclear fission reactors and nuclear weapons decommissioning. Moreover, mishandled radwaste could in principle contaminate the environment, people or, far worse, be used for the production of weapons. This is why all over the world there are regulations prescribing how the radwaste has to be handled and stored. Recently we have proposed a system for the online real -time monitoring of the radioactive waste repositories, consisting of an array of many radiation sensors to be deployed all around the radwaste drums [1]. In order to be suitable for mass deployment these detectors have to be small, cheap, robust, easy -to-use and reliable. The sensors we are going to describ e in this paper possess all these listed features.