In vivo thyroid monitoring for iodine-131 in the environment.

Monitoring of air and milk samples is done routinely around nuclear facilities that release iodine-131 to the environment. Results from these measurements are used to calculate dose rates to the thyroids of people who live near such facilities. These calculated dose rates have large uncertainty factors associated with them due to the complexity of predicting the movement of iodine-131 through the environment. This paper describes an effort to monitor iodine-131 directly in the thyroids of individuals living in the environment. A NaI(Tl)-detector system was assembled in the back of a truck for rapid and convenient measurements of members of the general public. The monitoring system has a minimum detectable activity for thyroid-bound iodine-131 of approx. 35 pCi which is sensitive enough to satisfy all legal requirements for environmental monitoring in the U.S.A. except for the child who receives iodine-131 continuously from a nuclear-power plant. Thyroid doses are calculated with more certainty from in uivo measurements than from measurements made on environmental and effluent samples.