ed to the
roadblock at the intersection of Broadway and the North Shelter Road.
The north shelter monitor informed the chief monitor of the sudden
evacuation of the north shelter, whereupon the chief monitor surveyed
the north shelter area and found intensities of only 0.01 and 0.02
roentgens per hour (R/h). The chief monitor then contacted the south
shelter and informed Dr. Bainbridge that the north shelter region was
safe for those who needed to return, that Broadway was safe from the
Base Camp to Guard Post 2, and that Guard Post 2 was now manned so
that personnel leaving for LASL could be checked out (1).

The chief monitor then returned to the south shelter and assembled the
monitors from the three roadblocks and Guard Post 4 to prepare for
entrance into the ground zero area. The time was about 0815 hours.
The military police at the roadblocks were given radiation meters to
survey the adjoining area. Broadway from the south shelter to Guard
Post 2 was remonitored occasionally to reassure the military police
that there was no radiation problem. Monitors also surveyed the Base
Camp for 24 hours after the detonation. No radiation above background
levels was detected there (1).

The following brief description of the radiological environment in the
TRINITY test area is based primarily on the results of the remote
gamma recorders situated in the test area and on results of the road
surveys conducted after the detonation (1).

Within about 1,400 meters of ground zero (except to the north),
radiation intensities between 0.2 and 1.3 R/h were detected during the
first few minutes after the detonation. These readings decreased to
less than 0.1 R/h within a few hours. At greater distances to the
east, south, and west, radiation levels above background were not
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