METEOROLOGY---FALLOUT AND WEATHERING
FIELD
THE SHORTER-TERM BIOLOGICAL HAZARDS OF A FALLOUT
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normally so much weakerjust above the surface
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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.
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QOLDFIELD
the surface to move a particle which is large
enough to extend into that layer, but it is
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still strong enough 100 or 200 microns above
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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
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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)
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Mr. Srencer (Bureau of Standards). T have
two questions. Have vou actually carried out
calculations of the time distribution of the
fallout?
Mr. Nacier.
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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
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WINTER GASE
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mate
OCCASIONAL SUMMER CASE
Frieure 5.—The Effect of Wind Structure on Fallout Patterns.