There are 37 known isotopes of Iodine, each with 53 protons but a different number of neutrons.
Iodine-127 is the most stable.
Iodine-131 is an unstable, radioactive isotope of iodine.
It is one of the radioactive materials that exploded from Chernobyl.
Iodine-131 mainly releases beta radiation.
Iodine-131 have a very short half life, so it releases its radiation VERY QUICKLY.
It is very dangerous to be around, and is one of the biggest feared products from nuclear power.
For the first few days after the blast, iodine-131 was a MASSIVE risk. Due to a short half life, iodine-131 is no longer a risk at the Chernobyl site (as it has been 37 years since the blast).
Half life graph for Iodine-131
When ingested, iodine-131 builds up in the thyroid gland causing thyroid cancer.
The iodine-131 that fell from the sky for days after the disaster landed on crops and in waterways, and the people of Ukraine were given no warning.