What is an essential factor for the production of X-rays?

The essential factor for the production of X-rays is a source of free electrons. In X-ray tubes, this is achieved through the process of thermionic emission, where the cathode is heated, causing electrons to be released. These electrons are then accelerated towards the anode, where they interact to produce X-rays through various interactions, primarily Bremsstrahlung and characteristic radiation.

The presence of free electrons is fundamental because without them, there would be no electric current to generate X-rays. The energy of the accelerated electrons is what contributes to the formation of X-rays upon striking the anode material. Thus, the availability of a source of free electrons is pivotal for the overall process of X-ray production.