eee ne
2
EVENT AND
eB.
DESCRIPTION
The estimated durations of fallout which
result from the above extrapolation of initial
fallout rate for Group I and Iil appear too
long to have occurred at the distances of
these people from the shot island, since the
wind velocity in the area was high enough
to move the cloud over the islands in a
considerably shorter time, as httle as one--
half of the above indicated time.
OF ENPOSED
Theaccounts of the visibility of the fallouls,
Doses calculated on a long fallout constant
rate of increase hvpothesis are lower than
those due to a short fallout, since a short
fallout quickly deposits a large amount of
activity. For both a 16 hour and 8 hour
fallout assumption, no dose value was estimated. The ranges are then as follows:
f
d. For Utirik atoll Group IV, onty a fallout
time of about 12 hours or less is consistent
with the later dose rates observed, provided
the fallout actually began as late as was
estimated from wind and distance factors.
e. A long fallout probably would not be umiformly heavy throughout, the first portion
being the most intense and the balance de-
creasing with Gime.
although conflicting, do net indiente such
late cessation.
—
GROUPS
The total phenomenon
_ would thus tend toward
shorter fallout.
the effect of a
This is supported by moni-
tor data from other nuclear events, where
intially heavy fallout is reported to produce
a peak of air-borne radioactivity soon after
arrival, with the airborne activity level then
decreasing.
The latter part of the fallout.
though still detectable as dust, may then
produce only a small fraction of the total
dose from material on the ground. Hence
the total dose may be estimated fairly accurately by assuming a constant fallout to
have been complete in a much shorter
“effective’’ time.
Table 1.2
LOr atiox
Faron? Thur
de AE
Rongelup (Group 1) ol... 39r
Afiinginae (Group JI}....)50
72r
Rongcrik (Group Pils... .
Vtirik (Group IV). 0202. . 1
|
1
TOr |
125
Shr
20
Gr
1W6r
War
The dose values given in Table 1.1, based on
film badee, meter and monitor data, are consistent with a constant fallout hypothesis of
about 12 hours effective time.” One exception
isinade: Che dose values for GroupIIT are about
79 percent of the 12 hour fallout value, averavwed
for 28.4 and 34 hour exposures.
This was felt
to express most accurately the average air dose
On Rongerik (Group IIT) a set of Alm badge
readings were obtained which constitute the
only direct evidence of (otal dose
Several
badges worn both outdoors and inside lightly
constructed buildings on the island read
about 50 to 65 r, and one badge which remained outdoors over the 28.5 hour period
read 98 r.
Another group of badges. kept
indoors inside u steel refrigerator, read 38 r.
These dose values represent a variety of
conditions, but. considering the shielding
and attenuation fnclors, are consistent with
the assumption that the dose outsidg during
the first 28.5 hours after the beginning of
the fallout corresponded to about 12 hours
of constant fallout.
9002 ibs
received by personnel who spent roughly half
their time inside structures where the dose rate
wis liter fonnd to be roughiv half that out-
doors. On the otherislands such shielding wag
not available.
Figure 1.8. illustrates
the cumulation
of
radiation dose asa function of tone after deto-
nation.
‘The dose rate varied comtinnuons)y.
The major portion of radition was received at
the lugher dose rate prevailing in the early por-
tion of the expocure period.
Tdy che time that
"Using 22 hours achially results in vadues which sre
hivher than these of Kable 2.) hy 3 te l)or, Tatde 2.1
listine the valves calcultted leefore all speetrum) dicts
wis avadhabde.
Uncerteinty iu all the infuurmation i+
greuter Chany this difference, which is neglected,