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METEOROLOGY---FALLOUT AND WEATHERING
THE SHORTER-THERM BIOLOGICAL HAZARDS OF A FALLOUT FIELD
SOIL ERODIBILITY AS A FUNCTION OF PARTICLE SIZE
Diameter (microns)
Less than 20
0 - 50
Relative erodibility
Non-erodible except at wind
speeds greater than 50 mph,
6 inches above ground,
Difficult to erode.
50 - 500
500 - 1000
More than 1000
Highly erodible.
Difficult to erode.
Non-erodible except at wind
speeds greater than 50 mph,
6 inches above ground,
Figure 6.~—Sotl Erodibility as a Function of Particle Size.
studies of local irregularities as they affectthe
fallout pattern?
Mr. Nacurr.
The question of irregularities
in the fallout pattern?
Mr. Spsncer. Inthe groundcontouras they
affect the fallout pattern.
.
Mr. Nacter. We knowthat these irregu
Jarities exist, but to my knowledge, there bas
been no good quantitative study of them. The
observed Nevada fallout pattern which I showed
is probably oversimplified, since most of the
monitoring runs are made in fairly broad, flat
valleys, Some features of rougher terrain must
act like snow fences and cause an irregular
piling up of the radioactive particles.
Dr. Werner, Are there any other questions
from the audience?
Dr. Stannarp (University of Rochester).
Could you give us some very average figures
for the fraction of activity on particle sizes too
small to settle out?
Mr. Nacrer. Thefraction not settling out is
quite dependent on the type of burst. We can
get an idea of this fraction by considering the
measurements of what fraction settles out.
For Nevada tower bursts perhaps 5 to 20 percent of the total radioactivity falls out within
the first 200 miles or so. For a surface explosion, where a great many morelarge particles
are formed, a much higher percentage mayfall
down, perhaps as much as 80 percent, within
this distance.
For an air burst, this percentage
falling down is almost negligible. In each case
some of the reniaining activity reaches ground
which had not heen affected. T don’t think
this would be a very dangerous effect. As far
as structures are coneerned, the airborne
particles would gradually infiltrate into homes
and so forth, much as dust does. 1 don’t know
quantitatively how important an effect this
would be. I would not imagine that it would
be too great an effect.
Dr. Werner. As I recall at Redwing, there
were some effects of this sort noticed on the
ships that were ont in the fallout pattern,
Passing through a rainstorm did have quite a
significant effect in reducing the level of radiation. However, here there was a convenient
waste disposal tank available which would not
be available in the case of land installations,
For land
installation,
decreased by weathering processes.
if you would comment. on that.
think
that
T wonder
Mr. Naaurr. I can cite an example of this.
We drove in very close to the remains of one
tower—that from the explosion on May 5,
1955—-just. a few davs after the test, The
levels of radioactivity were rather low on the
asphalt pad almost underneath the toweritself.
There had been rather strong winds. J would
suspect that from smooth surfaces like city
streets and buildings the wind erosion of these
particles will be rather large. On rough
terrain and in vegetation it would be rather
small, It must be a tremendously variable
thing. It would also depend upon how damp
Dr. Werner. Are there any further quesI would like to ask a question, if I
could. What would you expect the effect
would be of weathering on redistribution on a
rather large-scale fallout field and also on
structures?
Mr, Naauer. On a large seale field the
general effect would be to diminish the fallout
in the places where it was most dangerous.
Weathering would not have a concentrating
effect normally. It would tend to distribute
it and bring small amounts to other places
would
perhaps the intensity would not be appreciably
in a few days, but muchis on particles with no
significant settling velocity.
tions?
I
448029 O—58——~-2
the ground was.
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On very dry ground,particles
maybe picked up moreeasily.
Dr. Werner. Perhaps we have time for one
other question.
Dr. Newcomae (USNRDL). Do you have
any information on the possible screening
effect of vegetation in determining the amount
of fallout on the ground? 1 have in mind
availability io the animals on the floor of a
forest, for instance, as contrasted with a desert
area or grassland area.
Mr. Nauter. T believe that Mr. Larson of
UCLA has had some data on that, that the
leaves of plants do tend (o selectively collect
small particles, due to the rough structure, the
tinyhairs on theleaves, and eo forth.
So there
is actually a collecting mechanism which is
probablyiniportant in some types of vegetation
in intercepting and holding these particles,
making them more available to the animals.
This is an important effect. In Nevada we
don’t have the best place for measuring the
effect on foliage, but we feel this is an important
effect.
Dr. Werner. Thank you. T believe there
is one thing that impresses those of us who
have been concerned with the matter of predicting fallout field that Mr. Nagler has been
discussing and that is the variability. Even
under best conditions as you can see where the
impute data is determined, one canstill expect
rather large variations.