Iodine-131
- General: Its name is from the Greek word "iôeides," meaning "violet colored," after the violet color of iodine in a gas form. As a solid it is shiny, black and non-metallic. In its non-radioactive form occurs on land and in the sea in sodium and potassium compounds, and is necessary for proper functioning of the thyroid.
- Half-life: 8.04 days.
- Atomic number: 53.
- Decay mode: beta radiation.
- Sources: Fission product created in nuclear reactors and in nuclear weapons explosions.
- Release of iodine-131 per kiloton of fission explosive power: 125,000 curies.
- National Cancer Institute estimate of iodine-131 releases from the Nevada Tests: 150 million curies.
- Organ most affected: thyroid.
- Main pathway: milk.
- Other pathways: ingestion of other dairy products, vegetables, fruits, and eggs; inhalation; and external irradiation.
- Direct physical effects: radioactive iodine damages or destroys thyroid cells.
- Health effects: Increased risk of thyroid tumors, notably in children. Likely increase of thyroid cancer risk in children exposed before the age of 15 years. Children under five at highest risk. Females have more than twice the risk of males. Linked to other thyroid disorders, such as autoimmune hypothyroidism, autoimmune thyroiditis, hyperthyroidism incident to Grave's disease, and thyroid nodules.
- National Cancer Institute estimate of thyroid dose from Nevada Tests averaged over entire country: 2 rad.
- National Cancer Institute estimate of thyroid dose to children aged 3 months to five years in high fallout areas: 27 to 112 rad.
- Official iodine-131 release estimate from Chernobyl: 7.3 million curies -- decay-corrected to ten days after the start of the accident.
- Iodine-131 inventory in the Chernobyl reactor on April 26, 1986, the day the accident started: approximately 83 million curies.
- IEER's rough estimate of actual releases from Chernobyl over the course of the ten-day fire: 10 to 15 million curies (assuming the official estimate of a 20% release fraction is correct).
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Institute for Energy and Environmental Research
SDA Vol. 6 No. 2