B

When cathode rays, which are streams of electrons, collide with a target anode of high atomic weight, the kinetic energy of the electrons is converted into electromagnetic radiation. This interaction typically results in the generation of X-rays due to the deceleration of electrons upon hitting the heavy metal target. This process, known as Bremsstrahlung, occurs because high atomic weight materials have a dense electron cloud which leads to a significant reduction in speed and thus produces X-rays.
Therefore, the correct answer is B: X-rays.