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contributed little to the total radioactivity in the fallout.
As
much as 25 to 50 per cent of the total radioactivity returned to
the earth within a few hours.
During the present series, the nature of the releases of
gaseous material is such that the clouds formed do not rise to altitudes such as those from surface or near surface detonations,
but linger near the surface and are acted upon by the lower tropospheric and surface winds.
Normally, these clouds are so dis-
persed by the time they reach off-site populated areas that they
are difficult to detect with portable monitoring equipment.
How-
ever, in a few events, clouds have passed over areas where people
were located; hence, there have been some off-site radiation
exposures.
These exposures are documented on film badges fur-
nished to these people by AEC.
The highest exposure from fallout
recorded for an off-site individual was 438 m at Nyala, Nevada.
Due to the gaseous nature and rapid movement of these clouds,
stringent requirements are placed on the off-site monitors, who
must intercept the clouds and record radiation intensities during
passage of the clouds.
Airborne monitors locate and track the ra-
dioactivity and direct the mobile ground monitors into the path of
the clouds.
Unless there is a continuous recording air or back-
DOE ARCHIVE:
ground radiation instrument or a mobile ground monitor in an area
when a radioactive cloud passes, passage of the cloud can be
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