radioactivity in the samples is often limited to isolated areas
or "specks", most of which are assumed to be fallout particles.
The term "speck" contamination 1s used to denote spotty activity
on organisms, presumably caused from inscluble radioisotopes.
The identification and distribution of "specks" in sand, plankton, algae,
invertebrates,
fish and land plants are discussed
below.
Sand.
An autographic technique found useful for locating
these radioactive particles involved spreading sand on scotch
tape,
inverting to remove loose particles, and exposing with
firm contact against fast film.
After developing, a positive
transparency was printed on the film to be placed beneath the
sand sample so that when in perfect registry the radioactive
particles would be illuminated if viewed by transmitted light.
Engebi beach sand showed spots that were associated appar-
ently with only the finer sand particles.
Some of the active
particles were isolated by successive dichotomous civision of
@ sample of sand and retention of the more active half,
termined by the end window survey meter,
as de-
until the individual
particles which contribute most of the radioactivity could be
picked out under the microscope.
In Figure 17 sand samples
and active and non-active particles which have been separated
from the samples are shown.
Counting rates for the particles
are given in the legend for the same figure.
In Biijiri dredged sand radioactive particles were dif-~ferent in appearance from inactive particles.
~
86
”
Active particles
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