Realization and characterization of a protective coating for plastic scintillators used as sensors of radioactive contaminants in water

A new sensor for alpha particles based on plastic scintillators immersed in water was demonstrated to provide a viable solution for real-time detection of radioactive contaminants in water. It is obtained by stacking an array of plastic modules composed by a thin layer of Ag-doped zinc sulphide, ZnS(Ag), deposited on a plastic scintillator foil. Alpha particles are detected in the ZnS(Ag) layer, whereas beta are detected inside the plastic substrate. One still unexplored aspect of this novel detection technology is how the long-term contact with water affects the detector performance. To protect its surface from water-induced damages, we identified a coating protocol based on a poly(methyl-methacrylate) film deposited by spraying on the ZnS(Ag) active layer of the scintillator. The ageing process of the scintillator was carried out by using suitable aqueous solutions and the effect on the sensing layer was monitored by measuring its wettability and surface morphology. The performance of the coated scintillator was tested by measuring the efficiency with alpha radioactive sources.