After the initial gross activity was surveyed, samples of humanhair, grass, thatch roofing, and soil were analyzed for their beta and alpha activity (Table 4.9). The presence of fissile material on the thatch was of the order of 107° ng/g and on grass about one-half that on
the thatch, at 35 days postdetonation. The fissile material activity in human hair was quite
low.
TABLE 4,9—-Gross Beta and Alpha Activity of Soil, Grass, and
Thatch from Rongelap
Days
Sample
post-
detonation
Beta activity
(Sr® equivalent)
pe/e
Fissile material
(ue/g * 10°)
Thatch
T1-5
T6
35
56
2.7
1.6
1.3
35
0.5
0.3
67
67
0.09
0.03
S1 (organic)
41
0.10
0.47
$3 (surface)
67
0.06
3.0
Grass
G1-3
G4
G5
G6 (Utirik)
41
0.3
0.1
Soil
82 (sandy)
4.3
41
0.06
S4 (6 in. deep)
67
0.003
85 (Utirik)
87
0.006
0.03
1.9
0.8
SUMMARY AND CONCLUSIONS
The fallout material was found to consist largely of calcium oxide and calcium carbonate.
The fission products were adsorbed mainly on particles of 60 to 200 up. This material was 10
per cent soluble in water and completely soluble in acid.
Radioanalysis of soil and water samples from Rongelap indicated high levels of radioactive
contamination from the fallout at early times following detonation. Significant amounts of beta
activity as well as smaller amountsof fissile material were present on the external surfaces
of plants 42 days after detonation. Only small amounts of beta activity and no alpha activity
were detected in the edible portion of foods. It appears that during the first month a limited
amount of fission products is available to plants growing on contaminated soil. However, high
levels of activity in the coconut tree sap were detected which had an isotopic composition very
similar to that of the water analyzed.
Radiochemical analysis of thatch and water samples indicated a marked variation in the
ratio of Sr®, Ba‘“°, and the rare-earth group probably as a function of the different solubilities
of the radioelements. The activity of food, water, and soil samples from Utirik was approximately Yh of those of Rongelap.
It appears from this study that the ingestion of contaminated water was oneof the principal
sources of contamination for the Marshallese. Of the individual radionuclides, Sr®*, because of
its high solubility and relatively long half life, was probably the isotope of greatest potential
hazard in the environment.
47