Xe133

Xe133 is a radioactive isotope of the noble gas xenon with an atomic number of 54 and a mass number of 133. It comprises 54 protons and 79 neutrons, giving it a natural mass of 133.16 atomic mass units. The isotope is produced either by neutron activation of the more abundant Xe132 in nuclear reactors or by spontaneous fission of uranium-235 and plutonium-239 in spent nuclear fuel. After isolation, Xe133 is typically collected as a dry powder or dissolved in liquid xenon for further handling.

Xe133 is a β‑minus emitter with a half‑life of approximately 5.25 days. The decay proceeds primarily to iodine‑133, with the emission of a 81‑keV gamma photon. Because of its relatively short half‑life and the low‑energy gamma radiation it produces, Xe133 is considered relatively safe to handle with standard radiological precautions, such as using a glove box and maintaining a safe distance. In a medical setting it is inhaled by patients and used for functional lung imaging; the isotope migrates throughout the pulmonary system and emits gamma rays that are measured by a gamma camera, allowing clinicians to assess ventilation and perfusion of the lungs. In environmental science, Xe133 serves as a tracer for atmospheric transport studies, helping researchers infer air‑mass movement, ozone depletion, and the exchange of gases between the atmosphere and the ocean.

The isotope’s uses in both medicine and atmospheric research demonstrate the importance of noble gas radionuclides in contemporary science. Because of its short half‑life and low‑energy emissions, Xe133 can be deployed in portable diagnostic systems, but it must still be stored and transported in compliance with regulations governing radioactive materials.