Alpha radiation is the stream of alpha particles emitted when radioactive materials disintegrate. When radioactive material breaks down, there is a loss in the total mass of the products. According to the law of conservation of mass-energy there must be a corresponding energy release, which is the energy associated with the emission of the alpha particle. An alpha particle is a heavy nucleon, which is actually the nucleus of a heliumatom. They are most active in unstable elements of high atomic mass.
The stability of an atom relies on the balance of two forces, the force of repulsion among protons and the strong nuclear force. The number of protons in the atom influences the electromagnetic force by which the positively charged proton repels other (positively charged) protons. The strong nuclear force that holds the nucleus together is enhanced by the number of neutrons in the atom. There is a limit to the degree of influence that the number of neutrons has over the cohesion of the nucleus. When that limit is exceeded, the atom starts to lose particles. Because the alpha particle (the helium nucleus) with two protons and two neutrons is especially cohesive, the release of nuclear material is often in this form.
Alpha radiation is a result of alpha decay where a parent atom is profoundly changed through the release of alpha particles. With the release of each alpha particle, the atomic mass of the parent atom is reduced by 4 and the atomic number is reduced by 2. After a period of time, all atoms of a given amount of a radioactive element will reduce to a more stable isotope of that element or to a more stable element. This time period is measured by the time it takes for half of a given amount of atoms to be stabilized. One unit of this period is known as the half-life of the element. A half-life through alpha decay can be over five billion years (as with uranium) or as short as a fraction of a second (as with polonium).
The nature of alpha radiation was a mystery for a long time after its discovery. It is a fundamental part of the radioactivity first discovered by Marie Curie. Those studying radioactivity realized that the rays of radioactivity were not of the same composition. Ernest Rutherford was the one who first identified three types of rays as alpha, beta, and gamma. By introducing these rays to an electromagnetic field, Rutherford found that the beta rays were highly attracted to the cathodes and so must have been made up of negatively charged particles with low mass. Alpha rays were moderately deflected in a direction opposite to that of the beta rays. From these experiments, he was able to describe the alpha radiation as a stream of particles and not as a form of light as was previously believed. He discovered the alpha particles to be rapidly moving, positively charged particles with a high atomic mass. This mass was found to be nearly 7,300 times more massive than an electron.
One of the first practical uses of alpha radiation was as a nuclear probe. Long before artificial probes were available, subatomic researchers such as Rutherford relied on concentrated alpha radiation. Rutherford noted the rate of deflection of alpha particles shot at a gold foil. From this study, he developed his model of the atom as mostly composed of empty space but with a massive nucleus. Today, alpha radiation is used in smoke detectors. In these devices, alpha particles from radioactive material are allowed to complete an electric current.
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