Internal lrradiation The Rongelap people lived under conditions of severe radioactive conta- mination of their island for two days following the accident until they were evacuated from their island. This wasreflected in significant absorption of radioactive materials, from inhalation ingestion of contaminated food and water. Radiochemical urine analyses during the first 24 days showed internal levels of isotopes which were roughly estimated as follows in microcuries: Lodine!#!~®°, 6.4; Strontium*", 1.6; Barium!", 2.7: rare earths, 1.2; and smaller amounts of Cesium!, Strontium™, and Ce-Pr!'. Radioiodine probably delivered a dose of 100—150 rep to the thyroid glands of the people but absorption of radioisotopes was too small to result in any apparent acute effects. Rapid diminution of body levels of these isotopes occurred so that by six months urinary activity was barely detectable by gros counting methods. Only the indirect method for estimating the body burden based on urinary excretion rates was available until two years ago when a direct method of measuring body levels of gamma emitting isotopes becamepossible through the Fig. 9: Steel room used for gamma spectroscopy 324