a.
7
BUTTERNUT EVENT
OPERATION HARDTACK
1.
BUTTERNUT was ea barge shot situated 4,000 feet west of Yvonne
Island in the ligoon at Eniwetok,
The device was detonated at 0615M,
12 Mey ee The cloud rose to
35,000 feet, then stabilized at 30,000 feet.
Main cloud movement was to
the northvest, with most of the fallout deposited in the sea.
The only
islends receiving substantial contamination were Alice, with 650 mr, and
Mack (directly in the cloud’s path), with 30 r. Yvonne, less than a mile
from ground zero, read 100 mr.
All of the above rerditgs were surface
intensities corrected to H+3 hours.
2.
Fallout prediction was generally accurate, except that only the
northwest quadrant of the atoll received substantial contamination instead
of the whcle northern helf, as forecast.
Nearly all of the fallout fell
between the radials of 260 degrees to 300 degrees from ground zero.
Ilsngth
of the radials is approximsted at 110 miles; however, no direct observations
are available to bear out this estimate.
No fallout was detected outsides
BEST COPY tTSLABLE
the hazard area announced on D-1.
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TAB A
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