irradiated by internal sources; incorporated in body tissues. that is, by radionuclides These radionuclides gain entrance into the body through innalation or through contaminated food or water. Once inside they behave like their non-radioactive counterparts. Radioactive iodine, for example, accumulates in the thyroid gland in the same fashion as stable iodine, and radioactive strontium or calcium accumulate in the bone similar to their naturally occurring non-radioetive counterparts. The radioactive iodine will thus deliver a dosage to the thyroid gland that is many times larger than hat to the other organs or to the whole body, andthe ragioactive strontium and calcium will mainly irradiate the bone. Because of the uneven distribution of radionuclides in the body organs, radiation exposure standards have been develosed not just for the whole body, but also for individual orczans. In this report we will be referring to the maximum ' ermissible whole body and lung doses. Largely as a matter of convenience, secondary or derived raaiaztion standards have been developed. These secondary wv oO standards, wnich limit radionuclide concentrations or organ urdens, are often more easily employed than the primary dose tandards. We shall examine two secondary standards in this tas : . . = tae