. ‘ Volume 66, No. 6 June 1967 LATE EFFECTS OF RADIOACTIVE IODINE IN FALLOUT by such an explosion and its widespread 1215 or cE distribution has caused a series of high- energy discussions, and sometimes I think the temperature achieved by these discussions 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- onanSE TET, te aweSane a SE, clear devices; the second, radioactive prod- ucts from these devices; the third, local factors influencing the distribution of these products; and finally, the biological modu- Qa | a ba > = 2 wo wa mn l ioe i = i o 10% a a ad a loeb lation of the fallout products. Nuclear explosive devices are of two types, the first being the fission reaction that generally involves **5U, ?8°U, or plu- 10-4 l 70 _ 235 — py, P59 ! Ze ! 94 118 142 MASS NUMBER J 166 tonium. The fission produces an enormous variety of radioisotopes. There are also fu- Ficurz 1. Yield of various isotopes from nuclear reactions involving ™U and ™Pu. that we are presently discussing was a fusion explosion. However, all the fusion explosions have to be triggered by a fissiontype explosion in order to achieve the sion that produces either helium ortritium, may decrease, and finally there may be a relatively smooth curve. In general, however, fission produces an abundance ofisotopes with mass around 136 and mass around 94. Just why fission occurs asymmetrically is a matter of someinterest I will not discuss. It might be noted that most of the radioactive isotopes of iodine have a mass between 13] and 135 and hence are major fission products. There is an additional point of interest, and neutrons or, in the case of tritium, a namely, neutron excess. ?85U (a common fis- sion explosions, and the Bikini explosion necessary temperature required for fusion, whichis of the order of 10 to 100 million K. The fusion explosions are of two types: Theyare either the deuterium-tritium fusion that produces helium plus neutrons and energy, or the deuterium-deuterium explo- proton, plus energy. The points to remem- ber are [1] fusion explosions are impossible without fission so that there are always sionable material), for example, has 92 protons in the nucleus and 143 neutrons. If this were to undergo fission directly and fission gives an enormous increase in the There is an extensive series of palladium fission products, and [2] fusion added to number of neutrons present, and this has an effect on the distribution of the radioactive decay products. As far as the products themselves are concerned, there 1s an interesting distribu- tion curve (Figure 1). There are peaks at about 136 mass units and at about 94 mass units for the fission of 73U. There is a isotopes, and the most abundant of the stable ones is 1°°Pd, which has exactly half the number of protons of uranium. But since it has a mass of 106, it has 60 neu- trons. Therefore, if there were symmetrical fission of #85U, one would obtain 2 atoms of palladium and an excess of 23 neutrons. This implies that in a fission explosion there is an enormous neutron flux in the explosive’ device that irradiates the © fission products, the container, and anything t 1 ' 4 ’ re ren eae C3 rs f= eee slightly different curve for fission of 78*Pu and 755U, If the fission occurs in the presence of very high-energy neutrons the peaks symmetrically, it would produce palladium.