ee §.1 Introduction Fo.towine A Neueirandetonation in the spring of 1954, a Jurge group of people were containinated with fission products. Tn addinon toa sublethal external eamma radiation exposure and beta irradiation of (he skin, delectable amounts of radionuclides were deposited internally, It has heen assumed that in all situationsresuiting from a contaminating event, the “tio ofexternal to internal dose would be exceedingly high, Iowever, a detailed ‘study of the internal contamination in the exposed human population and in animals was made to determine the kind and dewree of internal deposition. Three general problems were investigated: (1) The determination of the con- tribution of the internal contamination to the acute radiation svndrome observed; (2) The possibility of long term effects, and (3) The qualitative and quantitative nature of. the internal contamination produced by exposure of individuals to mixed fission products. There Was no Hrevious situation in which humanbe- Ings Were exposed {o an environment contaminated with mined” fission products. -Concurrent studies were undertaken by the Japanese, however, on radioactive materials to which a small group of Japanese fishermen, near RongeJap at the time of the detonation, were exposed. The report of the extensive investigations undertaken on the ashes by the Japanese have been published (4). Evaluation of the internal contamination of the human beings was made by a study of the radioelements excreted: As very little infornation is presently available concerning the ratio of excreted radioelements to the anrount | deposited in the borly, it was necessary to base the evaluation on data ubtained from animals which had been contaminated in the same event. Detailed studies of anima) tissues and animal excreta then provided dita on which estinuites of the human body burden were based. 5.2 General Nature of Internal Radiation Toxicity Tuk Nature Orthe radiation hazard frominternally deposited fission products can best be understood in terms of the biophysical behavior of the radionuclides. _ Fission products entering the body through inhalation ur ingestion concentrate in various tissues and act as sources of internal radiation. The ability of a radionuclide to enter the blood strenm is determined byits solubility, chemical properties and physical state. The radioelements formed in fission are predominantly oxides which have a limited solubility in bady fluids. On this basis, only a few of the radioelements can becomeavailible to the body. However, the amount which can produce injurions effects when deposited within the body is minute because of the close proximity of the ixotape to the tissues it irradiates, and because the isotope continues to irradiate these Ussues’ until it is removed by biological turnover oris rendered harmless by radioactive decay. The effects of radiation frum internally deposited emitfers are the same as those from external radiation. ‘The disGngunishing feature of in-. ternal radiation, however, is its long contiauing nature. . Radioactive isotopes follow the same metabolic processes in the body as the naturally: occurring inactive isotopes of the same element and of chemically similar elements. Thus strontium and bariwn, which are analogous chemically to calcium, are deposited in the calcifying 1 ssneof the bone. Although nearly two hundred radioisotopes are produced in the hssion process, only a few are potential chronic Internal radiation hazards. These fission products, which are listed jn ‘Fable 5.1, constitute a high percentage of the fission yield, and localize chiefly in bene. The “bone-seekers” have, in G7 5002112