Radioactivity

Radioactivity is the process by which chemical elements decay from unstable to stable states by emitting sub-atomic particles and/or energy from molecules over a period of time ranging from infinitesimal fractions of a second to thousands of millions of years. Many elements exist in different isotopes, which are variant forms of molecular structure within elements of the same number and position on the periodic table of elements. Some isotopes undergo radioactive decay from an unstable isotope to a stable isotope. The process of emitting particles and energies can make radioactivity harmful to life since these emissions can be toxic or stimulate harmful growths or mutations in living cells.

The worst peacetime incident involving the release of radioactive material occurred in Ukraine in 1986, when part of the Chernobyl nuclear reactor station suffered explosions and fires resulting from human error. The radioactive material released into the atmosphere was spread over a wide area by [Page 1461]wind and led to the contamination of forests and land for many miles around. Thousands of people were killed as a result of the initial explosion, but many more were injured from poisoning and genetic mutation resulting from proximity to the radioactive material. The atomic bombs exploded by the U.S. military over the Japanese cities of Nagasaki and Hiroshima toward the end of World War II still produce genetic mutations and illnesses 60 years and more after the event.

In the case of radioactive decay, the “parent” isotope decomposes into a “daughter” isotope. Understanding the rate at which these forms of decay take place can yield very important information about the ages of astronomical objects and the nature and age of the universe itself. The decay takes two forms, known as alpha and beta. In alpha decay, the molecule emits a helium ion and reduces its mass accordingly. In beta decay, a series of different but related processes occurs which are characterized by the absence of a discrete change in energy and mass level. Wolfgang Pauli and Enrico Fermi studied these processes and such observations were instrumental in identifying the neutrino. However, the major figure involved in the early understanding of radioactivity was Marie Curie, with her husband Pierre and colleague Henri Becquerel, whose work is remembered by the use of her name as a form of measurement, as well as the awarding of two Nobel science prizes. Extensive exposure to radioactive substances ended Marie Curie's life.

A significant proportion of radioactivity around the world takes place according to “natural” processes—that is, through the decay of substances that are found in the earth's crust and have been present since a very early period of the history of the earth. Radioactive elements in nature are known as radionuclides, and more than 60 of these are known to exist. This presence may have resulted from the processes of planet formation, or may have been brought about by interaction with cosmic rays in the many years subsequently. Perhaps the most significant of these is radon, which is a gas that is part of the decay of a chain of elements beginning with uranium-238 and passing through radium-226 and ultimately ending with daughter nuclides of radon that include alpha-particle releasing substances such as polonium-210. Radon is present in many parts of the world and its radioactive decay can cause cancers and bone diseases that may be lethal to human and animal life.

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