Radiological Assessments for the Resettlement of Rongelap in the Republic of the Marshall Islands (1994) / Chapter Skim
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2. ENVIRONMENTAL SAMPLING AND ANALYSIS
2. ENVIRONMENTAL SAMPLING AND ANALYSIS
Pages 21-40
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From page 24... ...
There are two separate issues concerning contributions of soil radionuclides to the total dose: the exposure from "average" conditions and the probability that there are local regions of high concentrations of radionuclides, commonly referred to as "hot spots." The estimated contributions of soil ingestion and inhalation to the total dose are considered small -- ~.6°/O for all isotopes (Tables 6 and 12 in Robison et al., 19931. The concern with hot spots is that a chance encounter with an unusually high concentration of radionuclides might contribute a substantial dose; this issue is of concern mostly for plutonium and americium isotopes because of their longevity, although their contribution to the total average dose is normally very small.
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From page 25... ...
If soil plutonium concentrations were known to be normally distributed, the desired probability of a given concentration can be calculated from the cumulative distribution function of the normal distribution. However, probability plots of the soil plutonium data (e.g., Robison et al., 1993, Fig.
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From page 26... ...
The exact values of the hot spot probabilities and upper confidence bounds do depend slightly on the choice of transformation, but they are all small. If the observed values of soil plutonium concentrations are taken as representative of soil plutonium concentrations in unobserved areas of Rongelap Island, then the probability that a small area contains a high concentration of plutonium is extremely small.
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From page 35... ...
. ~i= D ~ 3 oh 9L 90 0~- Zip 8 b O ~ 1'nuoO°°[SD3Ul ~nucooo[~1 I: em.
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From page 36... ...
if the spatial correlation fourth in pit 22 is characteristic of the rest of the island, this small-scale positive correlation decreases the probability that a very small hot spot exists. Conclusions · The systematic sampling grid used by LLNE is a widely used, commonly accepted technique to sample environmental characteristics.
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From page 38... ...
Determination of strontium-90 content of aqueous samples required Reconcentration by coprecipitation with ammonium oxalate, dissolution in nitric acid and precipitation as strontium nitrate, dissolution in water, and precipitation of strontium carbonate. Pretreatment of soil and biota samples was the same as that of plutonium samples.
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From page 39... ...
Moreover, an earlier concern of the committee appears to have been eliminated. For a time, there was a considerable backlog of unanalyzed samples that were collected in a grid sampling program; lack of data on those samples would have impaired proper dose assessment on Rongelap.
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