Increased sensitivity in optical scanning of irradiated CR39 foils with liquid thin films

The MoEDAL experiment employs solid-state nuclear track detector foils around Interaction Point 8 to search for traces of highly ionizing particles. The selected material, CR-39, has been used in several experiments and is capable of detecting ionization tracks down to the level of oxygen ions. However, due to the high-radiation environment of the Large Hadron Collider, the material becomes opaque after chemical etching and exhibits strong scattering properties. This complicates the identification of low-ionization tracks. By deploying liquid thin films on both sides of the irradiated foils and using machine-vision techniques, etch pits in the foils can be detected and classified.