Caesium-137 has a half-life of about 30 years. However, as it is highly water soluble, in actual uses cesium-137 ions are easily accumulated in the body, where their biological half-life is 110 days.
Radiocaesium (caesium-137 or cesium-137) is a byproduct resulted from the nuclear fission of uranium. Caesium most commonly forms chemical compounds in the form of salts, which are highly water soluble.
People can be exposed to caesium-137 through nuclear fallout or, more commonly, through water-soluble products that contain traces, which thus carry beta and gamma radiation to the tissues (with higher concentrations accumulating in muscle tissue).
Exposure to caesium-137 can lead to cancer. If the exposure is very high, it can lead to instant death (this, however, is a rare case).