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The AEC announcement, according to the placard, calls for approx1-
mately 2.5 megacuries released to the atmosphere, and again there
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On the lower line of the placards is the amount of strontium 90
available for worldwide depositions based on a different method of
inventory calculation. The AEC has announced that approximately
92 megatonsof fission yield or 9.2 megacuries have been released to
the atmosphere. Estimates have been made that approximately 3
megacuries have fallen out. locally, leaving 6.2 available for worldwide distribution. One can therefore decay the 6.2 to the indicated
dates and estimate the amount left in the atmosphere and on the
ground. The numbers in the lower line, 5.5, 5.4, and 5.3, are these
values. The agreement between the two methods of inventory calculation is remarkably good considering the limited amount of sampling information.
At the present time there is considerable doubt whether there is as
much as 3 megacuries actually deposited locally. If this was smaller
than 3, and it might be as small as 1, then each of the AEC-derived
inventories 5.5, 5.4, 5.8 would be higher and a discrepancy much
greater. In such a case I think that the explanation for the discrepancy lies in the fact that more of the fallout occurred over the
ocean where we have not properly measured the deposition. I will
talk about this in a few moments again, since it will arise in connection with another matter.
Now, so far we have talked about the worldwide fallout before the
Soviet resumption of testing. I would like to showthe inventories
of the fallout on the third placard for 1958 and 1961 Soviet tests;
the 1958 findings are shown for purposes of comparison with the
1961 results. Up to the end of December 1959 approximately (0.63
megacurie had been deposited on the ground from the 1958 series.
This has been identified as of Russian origin by using the ratios of
short- to long-lived isotopes. Remaining in the stratosphere to the
heights of the aircraft measurements was approximately 0.17. The
total amount which we can account for is approximately 0.8 megacurie of strontium 90.
Mr. Ramey. That would correspond to 8 megatons offission yield?
Dr. Macutra. Yes, sir. This compares with the amount which Dr.
Libby has announced as having been injected in the stratosphere of
1.24 to 1.5 megacuries. There ts a difference between the 0.8 and the
1.25 and the 1.5. We believe that the likely explanation is inadequate
sampling. The deposition on the ground is probably low because we
do not adequately sample the oceans. We think there is more fallout
over the oceans than we are able to extrapolate from land stations.
This is the first of two discrepancies.
Inventory computations from Soviet tests in the fall of 1961 are
not nearly so good. The amount deposited on the groundis poor due
to incomplete observations because the data has not been brought up
to date due to analysis lag. As will be seen later, the fallout up to
March 1962 is about the same after the 1961 test as following the
1958 Soviet tests. Using this information. we have estimated 0.2
megacurie of strontium90 fallout. It has been caluculated that up to
70,000 feet the inventory of strontium 90 is about 1.3 megacuries.
The term “over” indicates that the values are probably greater than
listed over this. The total amount is in excess of 1.5 megacuries of
strontium 90.
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RADIATION STANDARDS, INCLUDING FALLOUT
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74