Some isotopes are stable, however radioisotopes are unstable and disintegrate, with the emission of three main types of radiation. Alpha emitters release a particle composed of 2 neutrons and 2 protons. The atomic number is therefore reduced by 2, and the atomic mass by 4.
Alpha particles are so heavy that even with low velocity their momentum is high.
They don't travel far, but when they collide with other molecules they do a lot of damage, therefore alpha emitters are considered to be quite hazardous. When a beta particle emitter decays, one of its extra neutrons is converted to a proton, increasing its atomic number by 1 without changing its atomic mass. The breakdown is accompanied by the emission of a negatively charged particle of low mass, called the beta particle, and an uncharged particle of low mass, called a neutrino. For example, hydrogen consists of just one proton and one electron. Gamma rays consist of electromagnetic radiation resembling X-rays.