detected (1).

The cloud drifted to the northeast, and higher gamma readings due to
fallout were encountered in this direction. About five minutes after
the detonation, a reading of 3 R/h was recorded 1,400 meters north of
ground zero. Several minutes later, the intensity there had increased
to greater than 7 R/h, and it continued to increase for several more
minutes. Gamma detectors 9,150 meters north of ground zero, however,
recorded no radiation above background levels. This indicated that
the cloud had passed over or near the 1,400-meter area and only
partially over the 9,150-meter area where the north shelter was
located. Subsequent ground surveys of this area found no gamma
intensities higher than 0.02 R/h (1).

Gamma radiation levels at and around ground zero were much higher than
in other onsite areas because of induced activity in the soil.
Twenty-four hours after the detonation, the gamma intensity at ground
zero was estimated to be 600 to 700 R/h. This estimate was based on
data provided by the tank crew that drove to ground zero to obtain
soil samples. The intensity decreased to about 2 R/h at 725 meters
from ground zero. Gamma intensities of 0.1 R/h or more were confined
within a circular area extending about 1,100 meters from ground zero
(except in areas of fallout). One week after the shot, the gamma
intensity at ground zero was about 45 R/h. After 30 days, intensities
at ground zero had decreased to 15 R/h, and intensities of 0.1 R/h or
more were not encountered beyond about 365 meters from ground zero.
Gamma intensities of 3 to 10 R/h were found at ground zero three
months after the detonation (1; 19).