Beta radiation is the emission of an electron from the nucleus of a radioactive isotope. This electron comes from one of the neutrons in an unstable nucleus. The weak nuclear force is involved, and the neutron is converted into a proton when the beta particle is emitted. This produces an isotope of the next element in the periodic table, a process known as transmutation. The emitted beta particle travels through air at close to the speed of light. However, it can be stopped by a sheet of aluminum foil greater than 0.12 in (3 mm) thick.
When French physicist Henri Becquerel (1852-1908) first discovered the property of radioactivity in 1896, he did not know that radiation consists of particles as well as energy. Beginning in 1898, Ernest Rutherford (1871-1937) conducted experiments to determine the nature of this radiation. One experiment demonstrated that the radiation actually consisted of three different types: a positive particle, a negative particle, and a form of electromagnetic radiation that carried high energy. Further studies on the mass/charge ratio of the particles supported the idea that the negative radiation, which he had labeled "beta", had the same charge and mass as the particle identified by J.J. Thomson (1856-1940) as the electron. By 1902 Rutherford and his colleague Frederick Soddy (1877-1956) proposed that a different chemical element is formed whenever a radioactive element decays. Rutherford was awarded the 1908 Chemistry Nobel prize for his work in explaining these processes.
Although they had discovered a new type of reaction, physicists strongly believed that the conservation laws of classical physics would still apply. This meant that the decay reaction should exhibit conservation of energy, conservation of linear momentum, conservation of angular momentum, conservation of electric charge, and conservation of the number of particles in the nucleus. Three of the quantities were conserved when the beta particle was emitted; however, energy and angular momentum appeared to be "missing". To satisfy these last two conservation laws, Wolfgang Pauli (1900-1958) suggested in 1934 that beta decay must involve a third particle that is neutral, has negligible rest mass and a spin of one-half, and carries away from the reaction the energy that appears to be missing. Enrico Fermi (1901-1954) named this particle the neutrino, Italian for "little neutral one"--its existence was accepted without evidence. It was not until 1953 that Frederick Reines (1918-) devised an experiment that successfully detected the neutrino; he received the 1995 Nobel Prize in Physics for that work.
During the 1930s, when scientists were experimenting with reactions that were produced by neutrons, Enrico Fermi and his associates discovered that a heavier isotope of uranium than is found in nature, uranium-239, will spontaneously give off a beta particle and change into a new element of one higher atomic number, 93; this element will also undergo beta decay to change into an additional new element, 94. The new elements were named neptunium and plutonium, respectively. This is the first record of the production of synthetic elements, known as transuranic elements. Early in 1999 synthesis of the element with atomic number 114 was reported.
More detailed explanations of beta decay were developed in the late twentieth century, following theories of the existence of unique particles that transmit the weak nuclear force. These particles, identified as W and Z, were finally discovered in 1983 by Carlo Rubbia (1934-), who was awarded the Physics Nobel Prize the following year (1984).
The decay chain of the most abundant uranium isotope uranium-238 to stable lead- 206 involves six different beta decay reactions. In addition, a number of radioisotopes, both natural and man-made, have been identified as beta emitters. Rubidium-87, one of the relatively abundant minerals in the Earth's crust, is a beta emitter; its half-life is 49 billion years. The ratio of the amount of the element produced (strontium-87) to rubidium remaining in the sample is one of the methods that is being used by geologists to determine the age of the rocks of the Earth. Some of these isotopes have been put to practical use in industry and medicine. Often their application depends on the half-life of the element.Tritium, the radioactive isotope of hydrogen that is produced in the atmosphere, is also a beta emitter. Its half-life of 12.33 years is the right range for age dating fine wines and other materials that contain a high percentage of water. Cobalt-60 is an example of a beta emitter of shorter half- life (5.27 years); it is being used in medical applications. Iodine-131 (half- life 8.04 days) is also used in medical applications.
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