In this work are used two types of detectors scintillation NaI(Tl) sizes (2"x2") ,(1"x1.5")for a comparative study between them and are used two sources of radioactive cobalt Co-60 has two energy (1.33&1.73 MeV) , cesium has energy (0.662 MeV) . and calculating the total area of the spectrum space scattering and area of peak optical and portability energy analysis, found the size large for crystal detector leads to probability escape photons outside the crystals to be less because it can reveal again and recorded pulse with pulse recorded by the electron apostate so increase the value of...