I-131

Iodine-131

Technogenic

β, γ radiation

Half-life: 8 days
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Main emission lines: 30keV, 80keV, 364keV, 636keV

Where detected

Iodine-131 is produced in nuclear weapons testing and nuclear reactor accidents. It is one of the main short-lived radioactive contaminants. It poses a great radiation hazard for humans and animals due to its ability to accumulate in the body, replacing natural iodine. It is used in medicine for radioiodine therapy of the thyroid gland. That is why you may encounter a person who has undergone such therapy, for example, in the subway.

I-123

Iodine-123

Technogenic

β, γ radiation

Half-life: 13 hours

Main emission lines: 27kev, 158keV

Where detected

Iodine-123 is a radioactive isotope of iodine used in nuclear medicine imaging, including single-photon emission computed tomography (SPECT) or SPECT/CT exams. The isotope's half-life is 13.hours, the decay by electron capture to tellurium-123 emits gamma radiation with a predominant energy of 159 keV (this is the gamma primarily used for imaging). In medical applications, the radiation is detected by a gamma camera.
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Iodine-123 is produced in a cyclotron by bombarding Xenon-124 with a proton. Xenon-124 either will absorb the proton and loses a proton and a neutron to form Xenon-123, or Xenon-124 will absorb the proton and loses two neutrons to form Caesium-123. Caesium will later decay into Xenon-123 while Xenon-123 will decay in Iodine-123