METEOROLOGY---FALLOUT AND WEATHERING FIELD THE SHORTER-TERM BIOLOGICAL HAZARDS OF A FALLOUT 8 i_ cues ,, Z / | deche _ ot neta 4 ey Imes ie oF B42 / normally so much weakerjust above the surface | ‘ fo 7 . a NEV. UTAH / in ua that it is unable to move a 20 micron particle. Dr. Bora (Brookhaven Laboratory). Would you care to comment on the importance of different soils in altering the particle distribution that the model that you propose deals with, and the resultant change in the fallout patterns? Mr. Nacurr. This is something which is really not very well known. Thedistribution of activity on coral from a Pacific atoll does not seom to be greatly different from that on Ne- vada sand, but it seems probable that the rubble of a bombed city would lead to quite a different distribution of radioactivity and particle size. 8 | / QOLDFIELD the surface to move a particle which is large enough to extend into that layer, but it is i / i still strong enough 100 or 200 microns above 09 bY OD SD wind speeds show marked radiation. cles are more easily blown away than smaller cover has a shielding effect. In conclusion, it might be well to emphasize the very greatvariability from time to time and place to place in the effects of weathering on deposited ralioactive particles. Any “average weathering effect”? must be used with caution. important phenomenon there. Mr. Spencer. One other question, Have you plans or have you actually carried out any mee so z ano AHEAD OF A STORM DISCUSSION Dr. Mircueui (Rand Corporation). I would like to know whythe particles of less than 20 microns are considered non-erodible. Also, it should be noted that snow due to particles that were settling very slowly or, essentially, just drifting past in the trade winds. The measurements T have seen from Nevada tests have not indicated that this is an Daal K. M. Nagler, U. S. Weather Bureau wind action likewise varies over a large range. Finally, fallout particles may be covered by wind-blown sand with a resulting decrease in served. In some Pacific tests, a considerable part of the dose received at some locations was seers) wre) Fraonn 4.~—-Sample Fallout Computation--Time and Space Analysis of Winds. Like rainfall, tion from particles still airborne has heen ob- ee Hw STATUTE MILES. variability, so that the erosion of particles by while the particles are actually falling? Mr. Nacier. No, notspecifically, but radia~ noe Nawtiratliniteelaetansachanhrnentambemctnnell particles will be partially shielded by the surrounding soil, Mr. Nacuen. Yes. Mr. Spencer. Have vou determined what percentage of the dose delivered is delivered = W.8. HAND COMPUTATION (TINE AND SPACE ANALYSIS OF WINDS) o 9 Mr. Srencer (Bureau of Standards). T have two questions. Have vou actually carried out calculations of the time distribution of the fallout? Mr. Nacier. 8 -&- This concept that large parti- © ones seems unlikely at first thought, but it has beenverified experimentally. The explanation, I believe, lies in the way that the wind speed decreases very close to the surface over which it passes. With moderate wind speeds ata few inches above ground, the force of the wind is EES tLe tee WINTER GASE wees i antend oo mate OCCASIONAL SUMMER CASE Frieure 5.—The Effect of Wind Structure on Fallout Patterns.