Figure 1: The detection efficiency and density of a 3 mm-thick CdTe semiconductor, Si semiconductor and NaI(TI) scintillation detector at gamma ray energy of 140 keV. CdTe has 76 %, 5.85 g/cm³, Si has 10%, 2.33 g/cm³ and NaI(TI) has 45%, 3.67 g/cm³.