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Representative Price. The limitation on the data from the Southern Hemisphere is due to the fact that we do not have the equipment
down there.
Dr. Macura. We have one sampling point in southern Australia.
I think the equality between hemispheres is probably real in view of
the fact that many isotopes, not only strontium 90, but, for example,
carbon 14 data seem to suggest that the Southern Hemisphere has
essentially balanced and equaled the Northern Hemisphere in content.
This may simply reflect the mixing of the debris between the hemispheres long after testing has ceased.
The second placard shows that one can compute inventories of
strontium 90 at various times. The placard shows them as of May
1960, November 1960, and May 1961. The observed worldwide atmospheric content derived from U.S. aircraft sampling are given by
the figures 5.3, 5.38, and 5.2. Youwill recall that strontium 90 has a
28-year half-life and should decrease about 214 percent per year.
Consequently, the observed small decrease is quite consistent with
one’ expectations.
SURISETCeRRRTLE
sa ope
I am not directing that question to you, but I am wondering if Dr.
Dunham or someone in the audience here could give us a feel for this
before he goes on. I think it is important that these numbers be
understood in relation to their practical application.
Dr. Dunuam. In termsof cobalt 60 exposures which are the way
most of the exposures are done—some are done with X-rays for mice
in large-scale experiments—it is a matter of a few hundred curies of
cobalt 60, and the mice have to be a certain distance from that source
in orderto get three-tenths of a roentgen a week and thatsort of thing.
In terms of strontium 90 in people, or in mice, rather, I think it
is in the region of a hundred microcuries per kilo that you begin to see
regularly bone tumors and things of that sort. Dr. Langham may
correct me on that, but I think that is about the lower level. How
about the Utah dogs? Do you recall? I think it is in that general
range.
Dr, Lanecuam. Around a hundred microcuries per kilo where you
begin to get effects.
Dr, Dunya. It would be a hundred-millionths of a curie to produce regularly effects in mice and in dogs.
Chairman Ho.irtetp. I think that puts it in perspective so it could
be understood, unless there is a confusion on microcurie and megacurie.
Dr. Dunuam. A megacurie is a million curies. A microcurie is a
millionth of a curie. A microcurie is a millionth of a millionth of a
megacurie.
Chairman Ho.irreip. Excuse the question.
Dr. Macnra. I would simply like to point out that of the total
amount of strontium 90 available for worldwide fallout approximately
80 percent had been deposited before the resumption of tests in 1961.
Anothersurprising feature, although based on very limited data in
the Southern Hemisphere, is that the Southern Hemisphere stratosphere appears to have about as much strontium 90 as the Northern
Hemisphere’s stratosphere despite the fact that virtually all of the
stratospheric injections have taken place in the Northern Hemisphere.
This is one of the unexplained meteorological factors that we have
yet to explain.
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RADIATION STANDARDS, INCLUDING FALLOUT