I125

Iodine-125, denoted 125I or I-125, is a radioactive isotope of the element iodine. It has 53 protons and a mass number of 125. It is produced in nuclear reactors by neutron irradiation of tellurium targets, followed by chemical separation. I-125 has a half-life of 59.4 days and decays by electron capture to tellurium-125, emitting low-energy gamma rays in the tens of keV range.

Because of its relatively long half-life and low-energy emissions, I-125 is used in a range of medical and research applications. In medicine, it is employed in brachytherapy, including seeds for prostate cancer and plaques for ocular tumors, where a localized radiation source delivers targeted dose. It is also used in radiolabeling procedures to tag proteins, nucleic acids, or antibodies for diagnostic assays and research. Additionally, I-125 serves as a calibration source for gamma-ray detectors and other laboratory equipment.

Safety and regulatory aspects are important for handling I-125. It requires licensed radiological practice, appropriate shielding, containment, and monitoring to limit radiation exposure. Because iodine concentrates in the thyroid, exposure to radioactive iodine must be controlled, and specific protocols govern administration, monitoring, and disposal in accordance with national and international regulations.