~Jd
Table 2
Estimation of Gamma Dose?
Group
designation
I. Rongelap
II. Ailingnae
IIT, Rongerik
[V. Utirik
No.
in
Approx. time of
commencement
64
H++4to6hr
i8
H++4to6hr
group.
28
157
of fallout
H+6.8 hr
H+22hr
Instrument readings
used in dose
Best estimate
of total gamma
H + 50 hr (16 people)
375 mR/hr, H+7 days
175
H+ 28.5 hr (8 men)
280 mR/hr, H+9 days
100 mR/hr, H +9 days
69
40 mR/hr, H +8 days
1+
Time of
evacuation
H+5lI hr (48 people)
H +58 hr
H + 34 hr (20 men)
Started atc H +55 hr
Completed at H+ 78 hr
andthefallout duration as ~12 hr, with most of
the dose delivered early in that period. The times
when people were evacuated from theislands are
shown in Table 2.
2. Gamma (Whole-Body} Dose
Thefallout (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 same estimated
dose of gammaradiation. The children may have
had a somewhathigher dose thanthat 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 affordedlittle attenuation of the radiation. The whole-body doses were
calculated from measurements with radiationfield
survey instruments held 3 ft above the ground,
made within a week after the detonation, bv ex-
trapolation to the time of exposure with the energy
spectrum and decay taken into consideration.
Table 2 showsthe calculated gammadoses for the
different populations exposed. The degree of hematological depression that developed later is consistent with the doses calculated. In view of the 47
geometry of exposure, the midline doses to individuals were higher than those obtained with the
usual bilateral exposure of x-radiation.?
3. Skin Dose
The dose to the skin surface was much greater
than the whole-body gammadose becauseofthe
large amount of beta radiation absorbed bythe
skin. The actual skin doses, although impossible to —
calculate, probably amountedto thousandsofrads,
calculations
dose in air (R)
78
andtheir range of 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 eachisland
group correlated 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 due to beta radiation
from fallout on the ground (estimated at Rongelap
to be 2000 rads at the level of the dorsum of the
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 part in superficial beta burns. The
average beta particle probably did not penetrate
much beyondthe basal layer of the skin (~ 100 4).
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 dueto
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 by collecting rainfall
from the roofs into catchments, and a slight rain
was reported on Rongelapthe night ofthefallout.
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-