Final answer:
Electrons in an x-ray tube are made available through thermionic emission, where thermal agitation ejects electrons from a hot filament, which are then accelerated and produce x-rays upon striking the anode.
Step-by-step explanation:
Electrons are made available in the filament of the x-ray tube by a process called thermionic emission. This occurs when electrons are ejected by thermal agitation from a hot filament in a vacuum tube. These electrons are then accelerated through a high voltage, which gives them kinetic energy. When these electrons strike the anode, they convert their kinetic energy into various forms, one of which is electromagnetic (EM) radiation in the form of x-rays. This is different from the photoelectric effect, Compton scattering, and ionization, which are other processes that can involve electrons but are not responsible for their emission in an x-ray tube.