The type of radiation that has zero rest mass and no charge is called a “gamma ray”. Gamma rays are a form of electromagnetic radiation, like X-rays and radio waves, but they have much higher energy and shorter wavelengths. Unlike alpha and beta particles, which have mass and electrical charge, gamma rays are pure energy and have no charge or mass. They are produced by the decay of atomic nuclei, and can penetrate through most materials, including human tissue. Gamma rays can be both beneficial and harmful, depending on the dose and the context in which they are used.