Cesium

Nuclear fission of ²³⁵U (or other fissionable materials) yields ¹³⁷Cs as a product. Although ¹³⁷Cs is not naturally present in the environment, it can be collected from nuclear reactor processing and then used as an environmental tracer. ¹³⁷Cs adheres tightly to porous sediments and will follow the movement of the sediment. By exposing sediments to ¹³⁷Cs and allowing this combination to move dynamically, gamma ray spectrometry can then be used to measure the activity of ¹³⁷Cs and monitor the movement of the radioactive sediments [404], [405], [406]. ¹³⁷Cs dating of sediments not older than 60 years is useful in natural and artificial lakes and other environments because of its widespread production and release during atmospheric nuclear weapons testing, which began in the late 1940s, plus subsequent releases, such as during the accident at the Chernobyl nuclear reactor in April 1986. The ¹³⁷Cs concentration profile in a sediment core can be matched with the historical record of ¹³⁷Cs release to determine the approximate age profile of the sediment [406], [407].

High-energy gamma rays from ¹³⁷Cs serve as food irradiation devices to remove bacteria and other harmful microorganisms (living single celled organisms such as virus, algae and fungus) from food. Although ¹³⁷Cs is not used commercially for large-scale food irradiation, it has been proposed that it can be used this way. Gamma rays from the radioactive ¹³⁷Cs destroy the DNA of organisms to enable foods to last longer (i.e. irradiation of fruits and vegetables stops the ripening process) and be contamination free [408], [409].