What is produced when a projectile electron interacts with an inner shell electron of the target atom?

When a projectile electron interacts with an inner shell electron of a target atom, it can result in the emission of characteristic x-rays. This process occurs when the incoming electron has enough energy to knock out one of the inner shell electrons (like those in the K or L shell). This creates an electron vacancy.

To fill this vacancy, an electron from a higher energy shell (outer shell) will transition down to the lower energy level, and in doing so, it releases energy in the form of x-ray photons. The specific energy of the emitted x-rays corresponds to the difference in energy levels between the two shells involved, leading to what is called characteristic x-rays. These x-rays are called "characteristic" because their energies are characteristic of the specific element of the target atom.

In contrast, other processes listed, such as Bremsstrahlung radiation, occur when electrons are decelerated in the vicinity of the nucleus, resulting in the emission of x-rays due to the change in kinetic energy. Compton radiation involves the scattering of photons rather than direct interactions with inner shell electrons, and photon energy itself does not correspond to a particular emission outcome in this context. Thus, the interaction between the projectile electron and the inner shell electron distinctly produces characteristic x-rays