Iodine Mössbauer spectroscopy. The other iodine radioisotopes have much shorter half-lives, no longer than days. Some of them have medical applications involving the thyroid gland, where the iodine that enters the body is stored and concentrated. Iodine-123 has a half-life of thirteen hours and decays by electron capture to tellurium-123, emitting gamma radiation; it is used in nuclear medicine imaging, including single photon emission computed tomography (SPECT) and X-ray computed tomography (X-Ray CT) scans. Iodine-125 has a half-life of fifty-nine days, decaying by electron capture to tellurium-125 and emitting low-energy gamma radiation; the second-longest-lived iodine radioisotope, it has uses in biological
Iodine test is not formed if only iodine or only iodide (I) is present. The colour of the starch complex is so deep, that it can be detected visually when the concentration of the iodine is as low as 0.00002 M at 20 °C. During iodine titrations, concentrated iodine solutions must be reacted with some titrant, often thiosulfate, in order to remove most of the iodine before the starch is added. This is due to the insolubility of the starch-triiodide complex which may prevent some of the iodine reacting with the titrant. Close to the end-point, the starch is added, and the