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of the United States soil sampling program and has collected many of
the samples himself, In the United States samples have been collected
pericdically from 17 sites in addition to sampling for special studies,
On a world-wide basis 51 sites were sampled in 1956 and most of these
sites are being resampled in March, 1958.
Samples are collected from
level open areas uncultivated and with low ground cover such as grass.
Samples are taken usually down to a depth of two inches and again from
two to six inches in depth.
The amount of Sr-90 found per unit area
sampled is readily converted to equivalent Sr-90 per square mile.
For
the first several years of sampling the top two inches contained practically all of the Sr-90.
Recent samples indicate penetration by som
of the Sr~90 to below this layer to a depth of several more inches,
It
has been clearly shown from these studies that in areas like Antofagasta,
Chile, where there is essentially no rainfall, there is practically no
Sr-90, i.e., 0.02 in 1956 as compared with 2,0 Sr-90 mefrat” in areas
within a few hundred miles with adequate rainfall (24).
Sr-90 values
in soils collected along the equator the same year ranged only from 1.8
to 2.9 mo/mi* in areas with average annual rainfall of from 50 to more
than 100 inches.
The data presented by Mr. Merril Risenbud at the JCAE Hearings (13)
clearly indicate that in terms of Sr-90/mi” fallout has been heaviest
across the Northern United States.
Present average values