Isotopes are the atoms that have in their nucleus an atomic number corresponding to the chemical behavior of that element. Since isotopes have the same number of protons, they all have identical chemical behavior. But, however, since their neutron numbers are different the isotopes of the same element may have different radioactivity. An isotope that is radioactive is called a radioisotope like iodine, which is important in our health. In radioactivity, the nucleus of an unstable isotope or element breaks down by itself and gives off rays and particles; the ratio of neutrons to protons for stable isotopes increases for heavier elements and the ratio for stability for the most stable isotopes.
Iodine is one of the earliest elements whose radioisotopes were used in nuclear medicine. The most common, stable form of iodine has an atomic number of 53 and an atomic weight of 127, this is because you have 53 protons plus 74 neutrons. These numbers mean that the nucleus is stable and not radioactive. However, a lesser stable form of iodine has 53 protons but only four extra neutrons, for a total atomic weight of 131. With too many neutrons in its nucleus, iodine is unstable and radioactive with a half life of up to eight days. Because of its radioactivity, Iodine 131 can be detected in the body, particularly in the thyroid gland.
Iodine can be used as a form of a solution in medicine as a germicide as well. In producing purple dye, its radioactive isotopes can also be used in medical diagnosis; for example it can be used to treat thyroid cancer and act as a tracer in the body to determine how well the thyroid is functioning. As a matter of fact, we humans need about 140mg of iodine a day. Foods such as fish, sea vegetables, and other foods of marine origin, are your dietary iodine in which is usually taken in. Iodine is also added to salt to make sure that people around the world get enough of their dietary iodine, called Iodized Salt.