SESSION IV DISCUSSION
901
plants is concerned, or are they tobe considered the same? Dr. Ward,
you made one computation.
WARD: Mine was only on cesium. I would also like to know the
answer. I suppose that it would have to do with the availability and
mobility of the different ions. I really don’t know. Dr. Hawley has some
data.
HAWLEY: So far, our experience has been limited to iodine. We
have certainly studied this question. On the surface at least, the statement that was made this morning was new to us, certainly to me. I
would agree with Dr. Ward that it would depend upon the mobility of
the ions or the particles being dealt with. When we weretalking about
iodine earlier, I did not mention a lot of things. One of them was that
we set up intentionally to sample and try to determine the rate from
airborne concentrations at which the iodine was coming back off the
grass. Also, we set the experiment up with a kind of pseudoparticle
Sizing arrangement, This was so that we could get some information
about the physical status of the material that would float around.It
looks as though it is very nearly gaseous within the limits of what we
are talking about, down to lu anyway. It is coming off appreciably, but
I can’t give you any numbers yet. We have the data, and we intend to
analyze and publish them.
Someone has asked me if we did any sizing in this iodine study.
My answer was that we did but probably in too simple a manner. Our
experimental farm in Idaho is located on the same grid that the Convair
or General Dynamics people used during some fuel-element meltdown
tests, which produced mixed fission elements. They tried to sample the
whole spectrum of things. Their data indicate that there is a marked
change in iodine behavior at about 1000 m from the ground, or surface,
release point. With the fairly rough instruments we are using, it looks
as if we might have about the same thing. For example, we found a
change in ratio between a fibrous filter and the backup carbon. The
ratio of activity between the two was very nearly 2 to 1, carbon to
paper, across this grid close to the release point; but at about 1000 m
or so, 1500 m in our last experiment, there was a marked change where
the ratio of collection, or efficiency of collection, was almost unity,
which indicated that somewhere in this range the iodine was behaving
more like a particulate. We are planning to watch these things in plantgrowth
rooms and environmental chambers,
and we are hoping to
Simulate them somewhat along the line of Chamberlain.
I think that it is an oversimplification to state that a particle, no
matter what it adheres to, is going to have about the same residence
time as another.