SLIDE 6
Duration of fallout. Duration of fallout is defined as the time fallout
begins up to the time of cessation. This should not be confused with the time
fallout begins up to the time of evacuation which is much longer. Peterson's
estimated duration of fallout of about 19 hours at Rongelap, appears to be too
long relative to the known wind velocity moving the cloud past Rongelap (Cr56)
and relative to the first-hand accounts of fallout duration given by the
Marshallese evacuated from Rongelap Island (Sh57). Rongerik Atoll was 65 km
(40 miles) further away from the detonation than wan Rongelap Atoll. An upper
limit of 16 hours duration at Rongerik Atoll was estimated by Sondhaus.
Fallout at the location of Sifo Island, Ailingnae Atoll was at the same
distance from the detonation site as the Japanese vessel which was
contaminated by BRAVO fallout. This fallout was named Bikini Ash by the
Japanese. Bikini Ash granule size was visible to the eye (Su56) and was
observed to fall for 5 hours (Ts55). Bikini Ash granule size is consistent
with reports that fallout was visible at Rongelap, Rongerik and Ailingnae.
Fallout would not have been visible at Utirik based on distance vs granule
size extrapolations and fall velocity considerations. Visual observations of
fallout arrival and cessation time were reported by many persons at each of
these locations, (Sh57, Ts55) except Utirik, and were in reasonable agreement
with Dunning's values.
Lessard estimated duration time based on granule size
of Bikini Ash, the relative positions of the atolls and the fishing vessel,
and granule fall velocity estimates (Le84b).
DURATION OF FALLOUT
Hours
Location
of People
Distance
from Ground
Zero
1956
Sondhaus
1957
Dunning
1981
Peterson
Ailingnae
Rongelap
Rongerik
150 km
210 km
270 km
12
12
12
5.5
5.5
_
10
19
17
5
7
9
Utirik
570 km
12
3
19
17
11
1984
Lessard