Isotope

Name:
Isotope
Detailed information:
One of two or more forms or species of an element that have the same atomic number, i.e., the same position in the periodic table, but different masses. The difference in mass is due to the presence of one or more extra neutrons in the nucleus. Thus, “regular” hydrogen, with atomic number 1 and a mass of 1 (proton), is one of the three isotopes of hydrogen. The other two are the naturally occurring deuterium, which has a neutron in its nucleus as well as a proton, giving a mass of 2; and the artificially produced tritium (1 proton and 2 neutrons) with a mass of 3 (approximately). The atomic weight of an element is the average weight percent of all its natural isotopes. The heavier isotopes usually occur very rarely in the atomic population (1 part in 4500 for ²H, and 1 part in 140 for U-235; in the exceptional case of chlorine, the ratio of isotopes 35 and 37 is about 3 to 1).The occurrence of isotopes among the 83 most abundant elements is widespread, but separation methods are complicated and costly. Twenty-one elements have no isotopes, each consisting of only one kind of atom (see note below). The remaining 62 natural elements have from 2 to 10 isotopes each. There are 287 different isotopic species in nature; noteworthy among them are oxygen-17, carbon-14, uranium-235, cobalt-60, and strontium-90, all but the first being radioactive.There are three kinds of isotopes: (1) natural nonradioactive, (2) natural radioactive, and (3) artificial radioactive (made by neutron bombardment).Note: According to this definition, it is strictly improper to refer to elements that exist in only one atomic form as having “one isotope”; actually such elements as beryllium, aluminum, arsenic, iodine, and others have no isotopes, that is, they have no other atomic form that is like them in all respects except mass. The term isotope requires the existence of at least two elemental forms, in the same sense that the word twin requires the existence of a pair.

Use:

(Nonradioactive.) Preparation of heavy water to moderate nuclear reactors. (Radioactive.) Tracers in biochemical, metallurgical, and medical research; in geochemical and archeological research (14C); irradiation source for polymerization, sterilization, etc.; therapeutic agents in various diseases (iodine, sodium, gold, etc.); electric power generation.See Aston; Chemical Dating; Radioactivity; Heavy Water; Decay; Tracer; Nuclide.