I-131 is also a major fission product of uranium-233, produced from thorium.
Due to its mode of beta decay, iodine-131 is notable for causing mutation and death in cells that it penetrates, and other cells up to several millimeters away.
They had to be fully autonomous, because they were situated hundreds and hundreds miles aways from any populated areas.
After reviewing different ideas on how to make them work for a years without service and any external power supply, Soviet engineers decided to implement atomic energy to power up those structures.
For this reason, high doses of the isotope are sometimes less dangerous than low doses, since they tend to kill thyroid tissues that would otherwise become cancerous as a result of the radiation.
It is therefore said to be 'fissile' and we use the expression 'nuclear fission'.
Since atmospheric carbon 14 arises at about the same rate that the atom decays, the Earth's levels of carbon 14 have remained constant.
In living organisms, which are always taking in carbon, the levels of carbon 14 likewise stay constant.
Most carbon atoms have six protons and six neutrons in their nuclei and are called carbon 12. But a tiny percentage of carbon is made of carbon 14, or radiocarbon, which has six protons and eight neutrons and is not stable: half of any sample of it decays into other atoms after 5,700 years.
Carbon 14 is continually being created in the Earth's atmosphere by the interaction of nitrogen and gamma rays from outer space.