Atoms of the same element which are identical in their chemical behavior but different from one another in the number of neutrons contained in their nuclei, and thus have different atomic weights. In common usage, isotopes that are radioactive are known as radioisotopes.
Isotopes have an important role in industry as production aids, serving in three basic fields: (1) as tracers and gauges, “super-detectives” for monitoring and controlling a wide variety of industrial operations; (2) in place of X-ray machines, as cameras for spotting machinery faults and wear; and (3) as catalysts or active agents in creating and modifying materials.
Isotopes also act as flow tracers for detecting leaks in buried or inaccessible equipment. In a typical case, a leak was suspected in the copper tubing of a heating system buried in the concrete floor of a factory. A small amount of a radioisotope (iodine-131) was added to the water of the heating system. A Geiger counter quickly located the increased radioactivity at the leak; the break was repaired by removing a section of flooring only 15 cm (6 in.) long.