More and more experiments need materials with extremely low radioactive content. The require-
ments on contaminations levels are becoming so strict that "standard" techniques can not reach the
sufficient sensitivity to determine if a material complies with the specifications. In this contribu-
tion I use two widely applied materials (crystals and copper) as examples to show the main issues
in the achievement of a high radio-purity. Than, I present two newly developed technologies to
probe bulk and surface contaminations of several materials with unprecedented sensitivity.