This lecture covers the physical models for X and gamma-ray imaging devices, including the uses in medical imaging and security scanners. It discusses the interesting aspects of modelling, X-ray sources, radiation matter interaction, detector system architecture, and various types of detectors such as radiological plates, gas detectors, scintillator detectors, and semiconductor detectors. The lecture also delves into semiconductor materials, detector parameters, energy resolution, comparison with scintillation detectors, position resolution, signal current, induced charge, Ramo's theorem, and charge transport mechanisms.