Cesium137

Cesium-137 (Cs-137) is a radioactive isotope of the chemical element cesium. It is produced as a fission product in nuclear reactors and during nuclear weapons tests. Cs-137 decays by beta emission to metastable barium-137 (Ba-137m), which then emits a gamma ray as it decays to stable barium-137. The primary gamma emission has an energy of 0.662 MeV. Cs-137 has a half-life of 30.17 years, making it relatively long-lived in the environment and a persistent radiological contaminant if released.

Chemical and physical properties aside from radioactivity are similar to other cesium compounds. In practical use, Cs-137 is often contained in sealed sources or incorporated into cesium salts for transport and shielding. The gamma radiation emitted by Cs-137 allows it to function as a strong, penetrating radiation source without the need for a particle accelerator.

Applications include medical and industrial uses. It has been employed as a sealed gamma source for radiotherapy and brachytherapy in certain cancer treatments, as well as in industrial radiography, moisture-density gauges, and calibration devices. In some settings, Cs-137 sources are used for sterilization of medical equipment and for food irradiation, though other isotopes and technologies are also common in some regions.

Safety and regulation are central to Cs-137 handling. External exposure arises from the 0.662 MeV gamma photons; ingestion or inhalation poses internal dosimetry risks. Sealed sources minimize release risk, but accidents or improper disposal can lead to environmental contamination. Cs-137 was a major contaminant in several nuclear accidents, underscoring the need for strict licensing, shielding, monitoring, and proper waste management.