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Iodine is an essential trace element, found in many foods and an essential part of thyroid biology. Iodine-125 is a synthetic radioisotope produced for medicine, with a half-life of about 59 days.
Iodine-125 emits low-energy gamma radiation and Auger electrons over a very short range. Its long half-life and weak, localised emissions make it unsuitable for whole-body imaging but ideal for sealed sources that deliver a slow, confined dose, and for laboratory labelling where a durable radioactive tag is needed.
Iodine-125 is most familiar in brachytherapy, where small sealed seeds are implanted to treat prostate cancer and ocular melanoma from within the tissue. It is also widely used in research, labelling molecules for laboratory assays and binding studies across biology and drug development.
Iodine-125 is predominantly reactor-produced, formed by neutron irradiation of enriched xenon-124, which captures a neutron and decays to iodine-125.
StandardX is developing accelerator-based production as an alternative to strengthen and localise supply of iodine-125.