What type of emitter is 125I?

125I, or Iodine-125, is classified as an electron capture radionuclide. In electron capture, the radionuclide absorbs an inner orbital electron, which leads to the conversion of a proton into a neutron. This process results in the emission of X-rays and neutrinos. Iodine-125 is primarily used in medical applications, particularly in brachytherapy for cancer treatment, due to its ability to provide localized radiation with minimal impact on surrounding healthy tissues.

While Iodine-125 does emit gamma radiation as part of its decay process, its primary mode of decay is through electron capture, making it mainly classified as such. The distinction is important in medical dosimetry, as the type of radiation emitted influences how it can be applied for therapeutic purposes and how it interacts with biological tissues.