Radiochemical Analysis

a branch of analytical chemistry comprising an aggregate of methods for qualitatively determining the composition and content of radioisotopes in the products of transformations. Radioisotopes may arise from nuclear reactions both in natural substances and in specially irradiated materials. In contradistinction to radiometric assays, which determine the content of radioactive elements using physical instruments, radiochemical analysis establishes the content of radioisotopes in substances using chemical methods of separation and purification.

The identification and quantitative determination of radioisotopes are accomplished by measuring the gamma or alpha radioactivity of irradiated targets or of natural substances with alpha-ray or gamma-ray spectrometers. Radiometric apparatus permit the analysis of complex mixtures of radioisotopes without destruction of the original substance. In the analysis of substances containing a large number of radioisotopes or substances in which the relative concentrations of various radioisotopes vary greatly, the original substance is dissolved in water or acid; this is also done in cases where the decay of the radioisotope under study is accompanied by the emission of only beta particles or X rays. Isotopic or nonisotopic carriers are added to the solution and various chemical operations are carried out on the mixture in order to separate and purify the elements being investigated. The most common operations include methods of precipitation, extraction, chromatography, electrolysis, and distillation. The radioisotopes, which are isolated in radiochemically and chemically pure states, are then identified and their specific activities determined using radiometric spectrometers and counters of nuclear particles. The harmful effect of radioactive emissions requires adherence to special safety procedures.

Modern radiochemical analysis has been widely used in solving the many analytical problems that have arisen in connection with the production of nuclear fuel, the discovery and study of the properties of new radioactive elements and isotopes in activation analysis, and the investigations of the products of various nuclear reactions. Other uses of radiochemical analysis include the detection of the radioactive products of nuclear explosions on the surface of the earth and the study of the radioactivity of meteorites and surface layers of the moon induced by cosmic radiation.