The study of very low energy neutrinos requires a suppression of the natural radioactivity. This is what Borexino succeeded to achieve.
Technologies of the Borexino experiment: Introduction
Technologies of the Borexino experiment: Introduction Gianpaolo Bellini (guest editor) Int. Jour. Of Modern Physics Vol. 29 (2014) n. 16. DOI: https://doi.org/10.1142/S0217751X14020023