It has a range of applications in the production of electricity, in electronics, and in chemistry. The radioactive isotope caesium-137 has a half-life of about 30 years and is used in medical applications, industrial gauges, and hydrology.Although the element is only mildly toxic, it is a hazardous material as a metal and its radioisotopes present a high health risk if released into the environment.aesium is an alkali metal and has physical and chemical properties similar to those of rubidium and potassium. The metal is extremely reactive and pyrophoric, reacting with water even at â116 Â°C (â177 Â°F).