 Xenon-124 absorbs a proton and immediately loses a neutron and proton to form xenon-123, or else loses two neutrons to form caesium-123, which decays to xenon-123.The xenon-123 formed by either route then decays to iodine-123, and is trapped on the inner wall of the irradiation capsule under refrigeration, then eluted with sodium hydroxide in a halogen disproportionation reaction, similar to collection of iodine-125 after it is formed from xenon by neutron irradiation (see article on 125I for more details).Iodine-123 is usually supplied as []-sodium iodide in 0.1 M sodium hydroxide solution, at 99.8% isotopic purity.