Alpha radiation consists of clumps of two protons and two neutrons. These are usually called alpha particles instead of alpha radiation. These are the lowest-energy of the three types of radioactive emissions, and are the largest particles. Alpha particles can’t penetrate far into the human body by external exposure, but they are quite dangerous when ingested.
Beta radiation consists of electrons – one electron per radioactive decay. Although we are generally taught to regard electrons as a particle, when they are ejected from a radioactive decay event, they are often moving close to the speed of light and behave more like a form of energy. For this reason they are sometimes called beta particles and sometimes called beta radiation. They are much, much smaller and higher-energy than alpha particles, but have a lower energy than gamma rays. Its effects on the body fall between alpha and gamma radiation.
Gamma rays are high-energy, high-frequency electromagnetic radiation, similar to x-rays. Neutrons and larger clumps of protons and neutrons are highly damaging radiation, but they’re not normally emitted except as part of an uncontrolled chain reaction. In practical terms, gamma radiation can be the most dangerous type.