The proposed scattering model can be used to express the total charge implanted in an insulator for Polyethylene terephthalate (PET). Using experimentally determined quantities in the ion mirror image method (IMIM) inside a focused ion beam (FIB) microscope. The scattering model establishes a physical foundation for IMIM charge determination. After theoretically obtaining the trapped charge values, using MATLAB simulationand compared it with the practically trapped charge value of the polyethylene terephthalate material to check if there is a match between the both results.