Unethical human experimentation in the United States
In 1953, the AEC ran several studies at the University of Iowa on the health effects of radioactive iodine in newborns and pregnant women. In one study, researchers gave pregnant women from of iodine-131, in order to study the women's aborted embryos in an attempt to discover at what stage, and to what extent, radioactive iodine crosses the placental barrier. In another study, they gave 25 newborn babies (who were under 36 hours old and weighed from ) iodine-131, either by oral administration or through an injection, so that they could measure the amount of iodine in their thyroid glands, as iodine would go to that gland.
Iodine-123
I is the most suitable isotope of iodine for the diagnostic study of thyroid diseases. The half-life of approximately 13.13 hours is ideal for the 24-hour iodine uptake test and I has other advantages for diagnostic imaging thyroid tissue and thyroid cancer metastasis. The energy of the photon, 159 keV, is ideal for the NaI (sodium iodide) crystal detector of current gamma cameras and also for the pinhole collimators. It has much greater photon flux than I. It gives approximately 20 times the counting rate of I for the same administered dose. The radiation burden to the thyroid is far less (1%) than that of I. Moreover, scanning a thyroid remnant or metastasis with I does not cause "stunning" of the tissue (with loss of uptake), because of the low radiation burden of this isotope. (For the same reasons, I is never used for thyroid cancer or Graves disease "treatment", and this role is reserved for I.)