7
Table 2
Estimation of Gamma Dose?
I. Rongelap
IT. Ailingnae
II, Rongerik
IV. Utirik
Approx. time of
in
commencement
64
H+4to6hr
18
H+4to6hr
group
28
157
of fallout
H+6.8 hr
H+22hr
Time of
Instrumentreadings
Best estimate
used in dose
of total gamma
H+ 50 hr (16 people)
373 mR/hr, H+7 days
175
H+ 28.5 hr (8 men)
H +34 hr (20 men)
280 mR/hr, H +9 days
190 mR/hr, H+39 days
69
40 mR/hr, H+8 days
i4
evacuation
H+51 hr (48 people)
H+ 58 hr
Started at H+55 hr
Completed at H+ 78 hr
andthe fallout duration as ~12 hr, with most of
the dose delivered early in that period. The times
when people were evacuated from the islands are
shown in Table 2.
2. Gamma (Whole-Body) Dose
The fallout (where seen) resembled snow or mist
and was deposited relatively homogeneously so
that the individuals on each island were considered to have received about the sameestimated
dose of gammaradiation. The children may have
had a somewhathigher dose than that calculated
for the adults because, being smaller, they were
closer to the ground andreceived larger midline
doses. This possibility is supported by the higher
incidence of early nausea and vomiting and the
greater depression of blood elements in the young
children. The flimsy houses afforded little attenuation of the radiation. The whole-body doses were
calculated from measurements with radiation field
survey instruments held 3 ft above the ground,
made within a weekafter the detonation, by extrapolation to the time of exposure with the energy
Spectrum and decay taken into consideration.
Takle 2 shows the calculated gamma doses for the
different populations exposed. The degree ofhematological depression that developedlater is consistent with the doses calculated. In view of the 47
geometry of exposure, the midline dosesto individuals were higher than those obtained with the
usual bilateral exposure of x-radiation.?
3. Skin Dose
The dose to the skin surface was muchgreater
than the whole-body gamma dose becauseofthe
large amountof beta radiation absorbed bythe
st 1. The actual skin doses, although impossible to
c ulate, probably amounted to thousandsofrads,
calculations
dose in air (R)
78
and their rangeof values, due to different amounts
of fallout sticking to different areas, accounted for
the spotty nature and varying intensity oflesions.
The extensiveness of the beta burns in each island
groupcorrelated roughly with the amountoffallout visible on their island (see Table 6). Most of
the skin dose was dueto fallout deposited directly
on the skin, but some was dueto beta radiation
from fallout on the ground (estimated at Rongelap
to be 2000 rads at the level of the dorsum ofthe
feet, 600 rads at hip level, and 300 radsat the
head, on the basis of continuous exposure and no
shielding).? It was fortunate that the beta radiation had an average energy insufficient to penetrate deeply into the skin and therefore resulted
for the most partin superficial beta burns. The
average beta particle probably did not penetrate
much beyond the basallayer of the skin (~ 100 y).
However, since epilation occurred in many people,
the region of the hair follicles must have received
a dose equivalentat least to the minimalepilating
dose of 400 rads of 200-kVp x rays.
4. Internal Dose Calculations
Internal absorption of radioisotopes was due to
inhalation as the radioactive cloud passed over
andto ingestion of food and water contaminated
with fallout, water probably being a major source.
Drinking wateris obtained bycollecting rainfall
from the roofs into catchments, anda slight rain
was reported on Rongelap the nightofthefallout.
Since the cisterns were nearly empty, the dilution
effect was minimal. Water was being rationed at
that time, and it was drunk in spite of warnings
from the health aide. On Rongerik food and water
were better protected from fallout deposition.
Internal levels of radioisotopes absorbed from
the fallout were assessed by numerous radiochemi-
Mae _
designation
No.
ee de ee.
Group