by such an explosign. aad its widespread distribution has lO catisefi*a series of high- energy discussions, and semetimes I think the temperature achieved by these discussions has approximaged that of the cloud itself. 1215 LATE EFFECTS OF RADIOACTIVE IODINE IN FALLOUT | I will make a few general remarks about four different aspects of fallout@fom nuclear explosions. The first concerns explosive nu- clear devices; the second, radioactive prod- ucts from these devices; the third, local factors influencing the distribution of these products; and finally, the biological modulation of the fallout products. Nuclear explosive devices are of two types, the first being the fission reaction that generally involves #8°U, 2°U, or plu- tonium. The fission produges an enormous variety of radioisotopes. There are also fu- sion explosions, and the Bikini ‘explosion that we are presently discussing was a fusion explosion. Haweve¥ all thefusion explosions have to ‘be triggered, by a fissiontype explésion itt “order tg achieve the necessary temperature:tequ for fusion, whichis of the order e€ 10.to 2Q0 million K. The fusion expiosiens aite--8f -two types: Theyare either the deuterium-tritium fusion that produces helium plus neutrons and energy, or the deuterium-deuterium explosion that produces either helium or tritium, and neutrons or, in the case of tritium, a a | - Ww > 2 jo'b wm z - ow re ~ 107 oO r— a iJ a ioe 107 —— —— 1 70 233 py 239 [ f 94 8 MASS NUMBER 1 J 142 166 FicurE 1. Yield of various isotopes from nuclear re- actions involving **U and Pu. may decrease, and finally there may be a relatively smooth curve. In general, how- Pare nee Volume 66, No. 6 June 1967 ever, fission produces an abundance of iso- topes with mass around 136 and mass around 94. Just why fission occurs asymmetri- cally is a matter of some interest I will not discuss. It might be noted that most of the radioactive isotopes of iodine have a mass between 131 and 135 ence’ are major fission productgg« There is and -_ namely, neusé proton, plus energy. The points to remember are [1] fusion explosions are impossible without fission so that there are always fission products, and [2] fusion added to fission gives an enormous increase in the number of neutrons present, and this has an effect on the distribution of the radioactive decay products. As far as the products themselves are sionable maf tion curve (Figure 1). There are peaks at about 136 mass units and at about 94 mass units for the fission of 28°U. There is a fission of #85U, ofe -would obtain2 atorns of palladium and an excess of 23 neutrons. This implies. that in a. fission explosion there is an enormous neuffon flux in the — explosive device that irradiates the fission products, the container, and anything concermed, there is an interesting distribu- slightly different curve for fission of 28°Pu and *85UJ. If the fission occurs in the pres- ence of very high-energy neutrons the peaks