704470 Reprinted froni .-~ss.\Ls OF ISTERNAL~IEDICI~E, 1.01. GG, So. 6, June, 1967 Printed in U. S. A. Late Effects of Radioactive Iodine in Fallout Combined Clinical Staff Conference at the National Institutes of Health Moderator: JACOB ROBBINS, M.D., Bethesda, Maryland. Discussants: JOSEPH E. RALL,M.D., PH.D., Bethesda, Maryland, and ROBERTA. CONARD, M.D., Upton, New York Late Effects of Radioactive Iodine in Fallout Combined Clinical Staff Conference at the National Institutes of Health Moderator: JACOB ROBBINS,M.D., Bethesda, A4arylan.d. Discussants: JOSEPH E. RALL,M.D., PH.D., Bethesda, fMaryland, and ROBERTA. CONAUD,M.D., Upton, New York R. JACOB ROBBINS:During the nuclear Dr. Conard will describe the findings as D explosion testing in the Pacific Islands they have developed over the ensuing 12 in 1954, a combination of circumstances led years. He was a member of the original ex- to the accidental exposure of a group of pedition dispatched by the Atomic Energy Marshall Islanders, as well as some U. S. Commission and the U. S. Navy and thus Navy personnel and the crew of a Japanese can give us a firsthand report of the initial fishing vessel, the Lucky Dragon, to a radiation effects. The major emphasis of rather unusual sort of fallout. In addition this Confeience, however, will be on the to body surface irradiatioll that led to skin late effects that have become evident only burns and general body irradiation from in the last several years. These observations the surroundings that led to acute radiation highlight a subject that is currently of con- sickness, contamination of food and drink siderable theoletical and practical impor- with radioactive isotopes of iodine pro- tance-the effects of radiation on the thy- duced pathological alterations of the thyroid roid gland. gland. Largely through the perseverance of The Conference will be opened by Dr. Dr. Robert A. Conard of the Brookhaven Joseph E. Kall, Diiector of Jntramural Re- National Laboratory, the Marshall Jsland- search, National Institute of Arthritis and ers, both exposed and unexposed, have been Metabolic Diseases, who has participated the subjects of thorough, repetitive exami- in several ol the previous expeditions to nations by teams of observers sent by the the ,Marshall Islands and who just returned Atomic Energy Commission. with Dr. Conard a few weeks ago from the latest visit. Dr. Rall will discuss the general Received March 27, 1967; accepted for publica- problem of radioactive iodine in fallout tion March 31, 1967. This is an edited transcription of a combined fioin nuclear explosions. clinical staff conference at the Clinical Center, Be- thesda, Md., by the National Institute of Arthritis RADIOACTIVEIODINE IN FALLOUTFROM and Metabolic Discases, National Institutes of NUCLEAREXPLOSIONS Health, Public Health Service, U. S. Depaitment of Health, Education, and Welfare. DR. JOSEPH E. RALL:The heat generated Requests for reprints should be addressed to by a moderate-sized fission explosion gen- Jacob Robbins, M.D., Chief, Clinical Endocrinology erally results in a temperature of the order Branch, National Institute of Arthritis and Meta- bolic Diseases, Bldg. 10, Rm. 8-N-315, National In- of 10 million IC. The complexity of the stitutes of Health, lkthesda, Md. 20014. probleiiis associated with fallout generated 1214 Volume 66, No. 6 LATE EFFECTS OF RADIOACTIVE IODINE IN FALLOUT 1215 June 1961 by such an explosion and its widespread distribution has caused a series of high- energy discussions, and some times I think the temperature achieved by these discus- sions has approximated that of the cloud itself. I will make a few general remarks about four different aspects of fallout from nuclear explosions. The first concerns explosive nu- clear devices; the second, radioactive prod- ucts from these devices; the third, local fac- tors influencing the distribution of these products; and finally, the biological modu- lation of the fallout products. Nuclear explosive devices are of two I I I I types, the first being the fission reaction 70 94 118 142 I66 that generally involves ?a5U, Z33U, or plu- MASS NUMBER tonium. The fission produces an enormous FIGURE1. Yield of various isotopes from nuclear re- variety of radioisotopes. There are also fu- actions involving mU and "'Pu. sion explosions, and the Bikini explosion that we are presently discussing was a fu- may decrease, and finally there may be a sion explosion. However, all the fusion ex- relatively smooth curve. In general, how- plosions have to be triggered by a fission- ever, fission produces an abundance of iso- type explosion in order to achieve the topes with mass around 136 and mass around necessary temperature required for fusion, 91. Just why fission occurs asymmetri- which is of the order of 10 to 100 million IC. c;illy is a matter of some interest I will not The fusion explosions are of two types: discuss. 11 might be noted that most of the They are either the deuterium-tritium fusion radioactive isotopes of iodine have a mass that produces helium plus neutrons and between 131 and 135 and hence are major energy, or the deuterium-deuterium explo- fission pi-oclucls. sion that produces either helium or tritium, There is an additional point of interest, and neutrons or, in the case of tritium, a namely, neutron excess. 235U (a common fis- proton, plus energy. The points to remem- sionable material), for example, has 92 pro- ber are [I] fusion explosions are impossible tons in the nucleus and 143 neutrons. If without fission so that there are always this were to undergo fission directly and fission products, and [Z] fusion added to symmetrically, it would produce palladium. fission gives an enormous increase in the There is an extensive series of palladium number of neutrons present, and this has an isotopes, and the most abundant of the effect on the distribution of the radioactive stable ones is loePd, which has exactly half decay products. the number of protons of uranium. But As far as the products themselves are since it has a mass of 106, it has GO neu- concerned, there is an interesting distribu- trons. Therefore, if there were symmetrical tion curve (Figure 1). There are peaks at fission of ?S5U, one would obtain 2 atoms about 136 mass units and at about 94 mass of palladium and an excess of 23 neutrons. units for the fission of 23W. There is a This implies that in a fission explosion slightly different curve for fission of ZSgPu there is an enormous neutron flux in the and 235U.If the fission occurs in the pres- explosive device that irradiates the fis- ence of very high-energy neutrons the peaks sion products, the container, and anything 1004231 Annals of 1216 NATlONAI. INSTITUTES OF HEALTH CLIKICAL STAFF Internal Medicine around it, producing a variety of isotopes. significant only in relatively short-term fall- Most of these isotopes are radioactive and out because of its 8-day half-life, and for they decay, frequently in a very compli- many years it was not considered to be a cated way. The average number of isotopes serious hazard. 1321 has about 4.5y0 yield; in a chain before any given fission fragment it has a 2.5-hr half-life, so it is only im- reaches a stable isotope is through six dif- portant in very short-term fallout. has ferent daughter generations. a substantial yield, 6y0, and a 21-hr half- There are a number of isotopes of major life, so it is of some importance over the biological importance. First, there are two course of perhaps a week. 1331is another induced isotopes that should be considered. radioisotope of iodine; this has a 6.7-hr 14C is a trivial fission product, but because half-life and is important only for a few of the intense neutron source there is a days. nitrogen-neutron reaction giving 14C. It was There are some other isotopes from fis- estimated several years ago that at that time sion explosions that must be considered. the amount of l4C in the atmosphere was One is I37Cs, which still can be detected roughly 70% greater than before thc first in most exposed individuals in the Marsha11 atomic explosion. Islands. It is also a potential problem be- 24Nais another isotope that is largely an cause of rclatively long-term storage in induced isotope, and it is of particular im- muscle. Cesium is further worrisome in portance in nnderwater blasts or blasts that meat eaters such as Eskimos who eat cari- are at all close to seawater because of the bou. There is cerium, which has almost a sodium in the ocean. Under these condi- 2-yr half-life and a substantial fission yield, tions, a substantial amount of z4Na, which and finally barium. has a 14-hr half-life, can be forniccl, and The amounts of these isotopes formed are in short-term fallout this can be oE some perfectly enormous. Just one example: Ex- importance. plosion of a megaton bomb of the fission Therc arc thee or four other isotopes type produces enough radioactivity so that that are of importance for several reasons. if it is evenly distributed over 1,000 square 80Sr, lor exanipk, has a 5.3% fission yield; miles it will give in 1 hr a close rate of the that is, of 100 atoms of uranium, 5.3 atonis order of 1,000 rads/hr. Hence, a 30-min ex- (if normalized for mass) end up as "Sr, so posure to this amount of radiation would, this is n significant fission product. It a1.m in general, be lethal. This is for a I-mega- has a 28-pr half-life so that it will persist ton bomb, but you may recall that the for a long time.