Final answer:
In a fluoroscopy system with a selenium panel, ionization events are responsible for converting X-ray energy into free electrons, which are then detected to form an image.
Step-by-step explanation:
In a fluoroscopy system that utilizes a selenium panel detection system, it is the ionization event that converts X-ray energy into free electrons. This ionization event occurs when the incoming X-ray photons interact with the selenium. The energy from the X-rays is sufficient to eject electrons from the selenium atoms, creating free electrons in the process. These free electrons are then detected and an image is formed. This process is crucial in fluoroscopy, providing real-time imaging to help with various medical and diagnostic procedures. It is similar to how scintillators work in other types of radiation detection systems, which convert radiation energy into light before being converted to an electrical signal by photomultipliers for image construction.