Facts about Cs-137

Chemical properties

Extremely reactive metal, forms stable salts with most of anions. Usually occurs as crystalline well soluble compounds. The main problem with 137Cs, which is present in the form of salts, is its high water solubility.


Half-life is 30.17 years, β- and γ-radiation. One gram of 137Cs has an activity of 3.215 terabecquerel (TBq).



One of the byproducts of nuclear fission processes in nuclear reactors and nuclear weapons testing. Small quantities of 137Cs can be found in the environment from nuclear weapons tests that occurred in the 1950s and 1960s and from nuclear reactor accidents. 137Cs from accidents or explosions cannot be seen and will be present in dust and debris from fallout.


In small amounts: for calibration of radiation-detection equipment, such as Geiger-Mueller counters.

In larger amounts: in medical radiation therapy devices for treating cancer; in industrial gauges that detect the flow of liquid through pipes; and in other industrial devices to measure the thickness of materials, such as paper, photographic film, or sheets of metal.

Risk of exposure

Dangerous in the large, concentrated amounts found in radiation therapy units and industrial gauges. The sources in these devices are designed to remain sealed and keep people from being exposed; however, if these canisters are intentionally or accidentally opened, the 137Cs inside could be dispersed.
In addition, this contaminant can be released to the environment at accidental or intentional CBRN incidents.

Health effect

Large amounts of 137Cs can cause burns, acute radiation sickness, and even death. Exposure to 137Cs can increase the risk for cancer because of exposure to high-energy γ-radiation.

Internal exposure through ingestion or inhalation, allows the radioactive material to be distributed in the soft tissues, especially muscle tissue, exposing these tissues to the β-particles and γ-radiation and increasing cancer risk.