82 DISCUSSION ON TOPIC IT THE SHORTER-TERM BIOLOGICAL HAZARDS OF A FALLOUT FIELD nearby it in air: whether the ground acts more like a sink or a reflector for radiations. To follow your suggestion, I won't make a dissertation of it. The auswer is that the surface appears to act as either one under different circumstances, and apparently when the incidence is close to grazing, as it is a large distance froma not-too-high burst. of a nuclear spectrum of the material after it went through theshelter. Dr, Teresr. I don’t know, [ think this is something that people have neglected. Dr. Bonn. I think that is a very good point. ] know of no experimental data on it at all. Tf the energy is sufficiently low, the radiation will be less effective for the sameair dose. on the interpolation curves, even from the Dr. Bore. There is one point in Dr. Bond's presentation which strikes me as being very noteworthy, indeed, and this is his comment about neutrons and their presumptive depth dose curve, and the resultant biological effect. radiations, and they in turn to some extent, can almost be thrown away. Such a conelusion would be a surprise to some people. On the other hand, there are some bomb effects, weapon, the model holds pretty well. Build- ings, on the other hand, if they were close by, . would probably decrease the dose over what had been calculated for free air. As we saw hardest components of the radiation a great deal of the dose that is delivered at a large distance from the bomb comes from scattered Thus near the lethal dose range, bomb neutrons especially the lower energy ones, do not come from straight ahead but from the side; and occasionally the lowest energy photons even are back. scattered toward the bomb again. So some large dense volume, such as a concrete perhaps at very high doses of neutrons and volume of this scattering source would probably decrease the dose to some extent over that predicted for free air. mission of neutron effects through the whole building, that occupied a large part of the Dr. Crowxits. Are there any questions from the floor? Dr. Terust (NRDL). I would like to make a comment concerning this energy dependence. The comment I want to make is concerning the biological effectiveness of energies below the 250 KVP that was presented here. J am under the impression that for very low energies you do have a difference in biological effect, which is muchless than these higher energies. If this is the case, what I would like to know is what would be the effects of shelters; for instance, individuals will be in shelters. Air doses will be measured inside. Therefore, the LD-50 may be very muchdifferent because of degradation of energy in going through shelters. I was just wondering whether or not you want to make some more commentson that. Dr. Bonn. Before I could answer that, I would have to ask you to give me the energy gamma reys where there is primary damage to the cortex of the central nervous system fairly close to the body surface. In these instances neutrons as well as gamma rays might be effective. Butfor cases where trans- body is required, it looks like the self-shielding factor that is implied by this depth dose curve must markedly reduce the whole-bodyradiation effects due to the neutrons. There are few bombs where the neutron rep divided by this factor will become very important. — Dr. Bonn. I hasten to add, however, that again the curves I showed were calculated curves, and J have every reason to believe and physicists have assured me that these would be the worst case in the field. Again, we have no measured neutron depth dose curvesin thefield. Dr. Cronxirr. There is another problem of practical importance not directly commented on, Dr. Bond, and that is what proportion, in a fallout field, of a dose is coming from close in and what proportion from far out? How big an area does one haveto clear if you are at the center to effectively reduce the dose by a factor of 10 or 2 or whatever you wish? Dr. Bonn. I have seen several estimates of this, and Dr. Robertson in our laboratory carried out a calculation along these lines. The answer one gets depends to a large extent upon the assumptions made in the calculation. It appears definitely that at least half of the radiation comes from 10 meters away or more. I have seen other cstimates that most of the radiation comes from the order of 100 meters or more. Dr. Bora. The method I talked about could answer this question. The machine calcule-~ tions, if carried further would be susceptible to analysis in this regard. Youcould tell not only what the 4x spectrum wasat agiven point, but from what solid angle the radiation was coming. If there is a general interest in this, someof the people who generated the original material might be able to carry the problem further. A comparable solution can be made for the initial gamma case: that is, a spectrum can be generated as a function of angular distribution, and for penetration through shielding this information might also be valuable. 1 don’t think it has ever been done, but it certainly could be done. Dr. Bonn. This information is of great practical value in regard to the question that was asked, how muchof an area must be cleared. I will say again that in termsof the depth dose pattern obtained in the individual as we saw under these conditions we apply the curves corrected for inverse square. So as far as the depth dose patterns are concerned, it does not matter from what distances the radiation effectively originates. Dr. Cronkite. Are there any further questions or comments on any of the papers of this afternoon? I notice that everybody so far has rather artfully dodged what I still think is a rather essential part of this symposium, to somehow or other come along with an estimate or guestimate of really how effective is radiation in man. I would choose not to answer this myself, but I see Col. Maxwell, who has had a lot to do with fallout. After all, how can one assess the hazardif you are not willing to comment somewhat on the effectiveness in man? I think it is self-evident that any reanalysis of 83 the Japanese datahas (o take ina lot of practical considerations about wherethe individuals were, how far they were away from the bomb, how close they were to large conerete buildings, and so on. It may he a completely impossible question to answer, but 1 am sure that someone here is not so shy, other than Dr. Borg, that they are not willing to comment on the subject. Dr. Bora. Utilizing data concerning weapon type, yield, burst. height, and atmospheric density, I caleulated gamma-distance curves for the Nagaseki bomb. Casualties have been . reported in some detail for the Fuchi school in Nagasaki (Oughtsozon, A. W., and Warren, S., “Medical Effects of the Atomic Bomb in Japan,’ New York, McGraw-Hill, 1956, p. 68). There were some woodensheds in that building where apparently, as Dr. Bond and I looked it over the other day, approximately 50 percentof the inhabitants of the wooden buildings~-about 30 in number--died of radiation disease, and were presumably exposed fully to bomb nuclear radiations only. At this distance the free air calculation that I made was 600 roentgens. This is a weapon, whether we choose in general to discount neutrons or not, which did not have a large neutron contribution, If the remaining concrete structure of the school nearby served to decrease that dose even further, and if the tiles androofing, evenif they didn’t accountfor a great deal of shielding, had anyeffect, T would say about 100 or 150 roentgens less than 600 roentgens would be the I.D-50 for man for inilial gammaradiation. ‘The mortalityfigures are not agoodstatistical series, I will admit. Dr. Cronxirz. I cannot refrain from commenting somewhat further that I see people here sitting who are responsible for writing handbooks and who put these numbers in them. I would not want to go so far as to call them by name, but. possibly they would like to comment. Mr. Linpwarm (Chemical Warfare Laboratories). Obviously the sort of question that Dr. Cronkite is pushing for is one, is there such a thing that can be drawn up at the pres-