ground zero area to retrieve soil samples on 16 and 17 July. On two
trips, the tank passed over ground zero; on the others, it approached
to within about 90 meters of ground zero. The men scooped up soil
samples through a trap door in the bottom of the tank. One driver who
made three trips into the ground zero area received the highest
exposure, 15 roentgens (1).

This lead-lined tank was also used by ten men to observe the radiation
area. These men, traveling two at a time, made five trips into the
area on shot-day but never approached closer than 1,370 meters to
ground zero. The highest exposure among these ten men was 0.3
roentgens (1).

The next party to approach ground zero consisted of a photographer and
a radiological safety monitor. Wearing protective clothing and
respirators, the two men were about 730 meters northwest of ground
zero photographing "JUMBO" from 1100 to 1200 hours. "JUMBO," shown in
figure 2-7, was a massive container built to contain the
high-explosive detonation of the TRINITY device and to allow recovery
of the fissionable material if the device failed to produce a nuclear
detonation. The plan to use "JUMBO," however, was abandoned when the
scientists concluded that a fairly large nuclear explosion was
certain. The container remained on the ground near the shot-tower
during the detonation. Both the photographer and the monitor received
an estimated radiation exposure between 0.5 and 1 roentgen (1; 7).

The last party to "go in" on shot-day consisted of six men retrieving
neutron detectors. They entered the test area at 1430 hours. Three
of the men went to a point 730 meters south of ground zero to pull out
cables carrying neutron detectors located 550 meters south of ground