133Xe

133Xe, or xenon-133, is a radioactive isotope of the noble gas xenon (element 54) with a mass number of 133. It is produced in nuclear reactors by neutron irradiation of xenon and is used as a radiotracer in medical imaging and research. It has a half-life of about 5.2 days and decays by beta minus emission to stable cesium-133, accompanied by gamma radiation detectable by external gamma cameras.

As a gas, 133Xe can be inhaled as a tracer. In nuclear medicine, inhaled 133Xe is used for ventilation imaging of the lungs, with the gas’ distribution imaged to assess regional ventilation and identify areas with impaired gas exchange. The technique is part of ventilation-perfusion imaging protocols, and 133Xe has also been employed in historical studies of cerebral perfusion. Its use for cerebral applications is less common today but has contributed to functional imaging research.

Handling and safety considerations are important because the isotope emits radiation. 133Xe must be produced, stored, and administered in licensed facilities with appropriate shielding and ventilation. Its relatively long half-life allows imaging over several days but requires careful scheduling and radiation protection. As a noble gas, it is chemically inert, so its behavior in the body largely reflects physical distribution with minimal chemical interaction.

Production and use summary: 133Xe is produced by neutron activation of xenon in reactors, purified, and filled into sealed containers for clinical or research use. Its radiative properties enable external detection, making it useful as a gas-phase radiotracer for ventilation imaging and related studies. See also radiotracers and lung ventilation imaging.