Flash X-ray radiography (FXR) is one of the electro-optical imaging methods and the most important diagnostic tool in the field of homeland security to detect explosive materials or drugs, terminal ballistics and detonation research to register and study such high-speed phenomena even under the roughest conditions like humidity, dust, smoke, debris, and metal. Physical principles of FXR technology and imaging with hard X-rays are presented. In order to take image sequences of high-velocity impacts using FXR and intensified high-speed cameras for image separation fast solid-state scintillator screens are necessary to convert the X-ray radiation into detectable visible light. The thickness of a scintillator screen is a significant parameter because there is a trade-off between the spatial resolution and the sensitivity. A low thickness means a high spatial resolution but also a lower sensitivity. In a study we investigated the influence of scintillator thickness on the FXR image quality and the emission decay of the scintillation response called decay time. Physical parameters like spatial resolution, signal-noise ratio and contrast are used to characterize image quality. High-speed sequences of FXR images at frame rates up to 50kfps of experimental investigations on the ballistic impact behavior of various protective components against projectiles and applications in the field of military and security agencies are presented. Finally, as a result of a literature study, some applications of X-ray backscatter technology in the field of homeland security and border control are shown to detect suspicious organic materials such as explosives, drugs using and landmines fast decay solid-state scintillators.