Xenon glowing under electric discharge. (Source: © Ludmila / stock.adobe.com)

Chemical element with atomic number 54. It is a mostly unreactive, colourless noble gas. It is used in flash-lamps and arc-lamps as it produces blue light when excited by an electric discharge. Xenon lamps are also used in ruby lasers.

Radioactive isotopes of xenon are produced by fission reactions. Reactor poisoning can occur when there is a large accumulation of xenon in nuclear fuel because xenon absorbs neutrons. The concentration of xenon 135 increases mainly during start-up, shutdown, or low reactor power; at high reactor power, the amount of neutrons in the core is high enough that the resulting xenon is rapidly converted by neutron capture to stable ¹³⁶Xe, which no longer absorbs neutrons.