New liquid scintillation counter development using Silicon Photomultipliers

In case of a nuclear incident, a radioactivity level estimation is expected in a few hours for environmental samples. Liquid scintillation counting is a rapid technique to directly measure alpha and beta activities in aqueous samples. But main available commercial Liquid Scintillation Counters (LSCs) are too heavy and fragile to be used outside a laboratory. Thus the French Institute for Radiation protection and Nuclear Safety (IRSN) chose to develop their own LSC. The main objective was to develop a robust, light, small and easy-to-handle LSC taking into account quenching effects, able to measure energy spectrum, and discriminating alpha and beta particles. In order to get smaller and more robust LSCs, photomultiplier tubes (PMTs) were replaced by HAMAMATSU Multi-Pixels Photon Counters (MPPC®), also called silicon photomultipliers (SiPMs). The inconvenient of MPPC is their high dark noise compared to PMT which lead to a lower sensitivity for low energy beta emitters. But for our purpose, beta emitters of interest have high enough energies to be detected (e.g. 90Sr with a beta mean energy of 195.7 keV). First tests were performed with MPPC S13360-3050CS and S13360-3025CS to prove the measurement capabilities of such detectors. 14C standard, alpha and beta sources measurements were performed and gave a counting efficiency of a few percent. Thus such a technology is suitable for our purpose.