High density scintillation crystal with low afterglow is the key material wildely to be used to detect the ionization radiation. There are a number of scintillation materials available to detect the Ionizing radiation.

Ionizing radiation is high energy and short wave length radiation that can pass through those kinds of materials with low density. 

The high-density scintillation crystal is cable to capture a small portion of the ionizing radiation and the energy of the captured radiation will transform to visible light. The tensity of visible light is measured and analyzed by a set of the algorithms to determine what radioactive nuclide present in the scene.