cesium-137

cesium-137 is a radioactive isotope of the alkali metal cesium and is one of the most common fission products from the nuclear fission of uranium-235 and plutonium-239 in nuclear reactors and nuclear weapons. It decays via beta decay to the metastable barium-137m, which subsequently emits a characteristic 662 keV gamma ray. Due to its medium half-life, high solubility, and chemical similarity to potassium, it presents significant environmental and biological mobility, making it a major component of radioactive fallout.

Properties

Cesium-137 has a half-life of approximately 30.17 years, undergoing beta decay with a maximum electron energy of 512 keV to the metastable nuclear isomer barium-137m. This daughter nuclide has a short half-life of about 2.55 minutes and decays to stable barium-137 by emitting a prominent 662 keV gamma ray, which is a key signature for detection with instruments like Geiger counters and scintillation counters. Chemically, as an isotope of cesium, it behaves like other alkali metals, forming highly soluble compounds such as cesium chloride, which facilitates its rapid dispersion in aqueous environments and biological systems, mimicking the pathways of essential nutrients like potassium.

Production and sources

The primary anthropogenic source of cesium-137 is nuclear fission, produced in significant quantities as a yield product in both nuclear reactors and during the detonation of nuclear weapons. Major historical injections into the environment stem from atmospheric nuclear weapon testing, notably the tests conducted by the United States at the Nevada Test Site and the Soviet Union at the Semipalatinsk Test Site, as well as from severe nuclear accidents. It is also generated routinely in facilities like the Oak Ridge National Laboratory and Sellafield during spent nuclear fuel reprocessing. Minor natural production occurs from the spontaneous fission of uranium-238 and via neutron activation of stable cesium-133, but these sources are negligible compared to anthropogenic releases.

Applications

Due to its consistent gamma emission, cesium-137 is used as a radioactive tracer in hydrological studies to track sediment movement and in geophysical surveys conducted by organizations like the United States Geological Survey. In industry, it is employed in devices such as industrial radiography cameras for inspecting weld integrity, a technology utilized by companies like General Electric, and in level gauges for measuring liquid in tanks. Its most significant medical application was in teletherapy units for cancer treatment, such as those historically manufactured by Atomic Energy of Canada Limited, though it has been largely superseded by cobalt-60 and linear accelerators. It also serves as a calibration source for radiation protection instrumentation.

Health and environmental effects

Internal contamination with cesium-137, primarily through ingestion of contaminated food or inhalation of airborne particulates, is hazardous because it distributes uniformly throughout the body, particularly in soft tissues, due to its chemical similarity to potassium. The emitted beta particles and gamma rays can cause acute radiation sickness and increase long-term cancer risks, such as thyroid cancer and leukemia, by irradiating tissues. Environmental consequences are severe due to its long half-life and high solubility; it readily enters the food chain, contaminating agricultural products, livestock, and aquatic ecosystems, as documented in studies following the Chernobyl disaster. Regulatory bodies like the International Atomic Energy Agency and the Environmental Protection Agency establish strict limits for cesium-137 in food and water to mitigate these public health risks.

Incidents and contamination

The most significant dispersal events involve the Chernobyl disaster in the Soviet Union and the Fukushima Daiichi nuclear disaster in Japan, which released massive quantities into the atmosphere, leading to widespread contamination across Europe and the Pacific Ocean, respectively. The Goiânia accident in Brazil involved the breach of a discarded radiotherapy source, causing severe radiological contamination and fatalities. Other notable incidents include contamination from the Mayak production association in the Soviet Union, the Windscale fire at the Sellafield site in the United Kingdom, and detected fallout in regions like the Marshall Islands from United States nuclear testing. Ongoing monitoring by agencies like the Comprehensive Nuclear-Test-Ban Treaty Organization tracks global atmospheric levels of this isotope.

Category:Caesium Category:Isotopes of caesium Category:Fission products Category:Radioisotopes used in radiotherapy