When X-rays are produced

When X-rays are produced in an X-ray tube, high-speed electrons from the cathode strike a metal target (anode), such as tungsten [t1, t4]. The vast majority of the kinetic energy from these incident electrons—typically over 99%—is converted into heat rather than X-rays [t2, t3]. This occurs because most electrons undergo multiple collisions that result in excitation and ionization of the target atoms, dissipating energy as thermal vibration [t1, t5]. Only a small fraction (less than 1%) of the energy is converted into electromagnetic radiation through processes like Bremsstrahlung (braking radiation) or characteristic X-ray emission [t2, t3]. Due to this extreme heat generation, targets are often made of materials with high melting points and are frequently water-cooled or rotated to prevent damage [t3, t4, t5].

Sources

1. [1] https://www.ncbi.nlm.nih.gov/books/NBK537046/