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 portability energy analysis, and increase the volume of detectors cause increased probability for scattering Compton, In other words the increase in the probability of interaction effect photoelectric be less than the increase in the probability of interaction scattering Compton so the Net Area under the peak at less an increase of scattering spectrum