Final answer:
Iodine-131 and iodine-126 are isotopes of the element iodine, both used in medical applications related to the thyroid but with different nuclear properties. Iodine-131 is notably used for thyroid scans and treatments due to its radioactive nature and half-life of 8.04 days, decaying into xenon-131.
Step-by-step explanation:
Iodine-131 and iodine-126 are isotopes of the same element, iodine. They are chemically identical, meaning they behave the same way in chemical reactions, including in biological systems like the thyroid gland. A major way they differ is their nuclear properties – iodine-131 is radioactive with a half-life of 8.04 days and commonly decays to xenon-131, emitting a beta particle (electron) in the process. In contrast, iodine-126 has different nuclear characteristics.
Both isotopes are used in medical applications, but iodine-131 is notable for its use in thyroid scans and treatment of certain thyroid conditions. Since the masses of radioactive iodine used in such scans are minuscule, they're often mixed with non-radioactive (stable) iodine as a carrier to maintain normal chemistry and distribution within the body.
In the case of iodine-131 therapy, it's used both for diagnostic imaging of the thyroid as well as for treating overactive thyroid glands or certain thyroid cancers. Following a therapy, iodine-131 will gradually decay and leave the patient's system, a process that spans over several weeks due to its 8-day half-life.