32 SHORT LIVED FISSION PROPUCT GAMMA RADIATION THE SHORTER-TERM BIOLOGICAL HAZARDS OF A FALLOUT FIELD distribution from weapons is more that representing high energy neutron fission? different from that encountered in weapons? when he showed me different nuclide distribu- distribution, as well. Dr. Zonet. I am afraid I don’t know. Lf the fissioning process is the same, I see no reason why it should be different. That is for the U-235 fission product. If there is an appreciable amount of fast fission which uraniumor U-235 is not very different from the slow neutronfission spectrum. product distribution in your test might be This would, or course, affect the gamma ray © COMPTON DAT: @ PAIR DATA might lead to different levels, I do not know. Dr. Bora. Perhaps I can add a small bit to the last answer. The fission product distri- bution curves afterfission in different materials photons/Mev- fission are noticeably different. Fisstoning in plutonium as against uranium shifts the curve. Fissioning with high energy neutrons as opposed to low energy neutrons will raise the value of the distribution curvefor these who are familiar with such a curve. If some of the nuclides which are emitting important gamma spectra are on the portion of the curve shifted, there might bea significant difference in the gamma spectrum that results. Dr. Sint. Is there any possibility of venturing a guess as to the magnitude of this effect? | ; 9 to 20 30 ENERGY (Mev! Fravae 6-—Typical spectrum of fission product gamma rays from a rotation fuet belt. 33 In other words, for the 1.7 seconds run, the equipment was set to bombard 1 second, wait 1 second, count 1 second. Dr. Sir (University of California), Was there any reason to believe that the fission Isn’t it likely that the fission product Dr. Bora. Yes. I] must admit I am not much of an expert along these lines, I think the answer is probably ves. J] have asked this question myself of Dr. Spence at Los Alamos tion curves. He threw up his hands andsaid itis hard to know. There are so many nuclides that arc radiating that the chauces are good that these spectra are similar for each case, and that the fast spectrum of plutonium or natural Dr. Cronxirg. Are there any further ques- tions? Mr. Koca (Bureau of Standards). Howdid vou evaluate your absolute numbers of fissions and how accurate do you think your numbers are? Dr. Zosgev. That right now is the biggest source of error that we can see, The number of fissions is calculated and it is crudely caleujJated, admittedly. We have taken the weight of the sample, we have taken the cross section, and we have measured the flux. It is calcu- lated on that basis. We expect to make a better analysis of the source and we expect that this will then bring the error down a fair amount. We hope that the final error will be of the order of maybe 15 percent. think we can reduce it below that. I don’t