Many biochemical studies routinely performed by researchers, such as protein assays and DNA studies, require the detection of extremely minute quantities of material. However, such small quantities are usually undetectable by the Lowry assay, UV spectroscopy, and other conventional methods of chemical analysis. This problem was solved with the development in the 1940s of chemical tests that use radioisotopes to label the material in question before it is assayed. This technology has allowed scientists to detect substances at extremely low concentrations with extraordinary sensitivity.

Radioisotopes are alternative, unstable forms of common elements that carry extra particles (neutrons) in their nucleus. As a result of spontaneous nuclear decay, radioisotopes emit nuclear radiation. There are several kinds of emitted radiation, including alpha-particles, beta-particles, and gamma-rays. The isotopes most commonly used in radioisotopic labeling are those that emit á-particles, such as 3H, 35S, and 32P. Energy from the emitted á-particles can be easily...

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