2.3 ACTIVITIES AFTER 16 JULY 1945

On 17, 18, and 19 July, all personnel and visitors had to receive
permission to approach ground zero from the "Going-in Board." On
these three days, 21 groups were authorized to go beyond the Broadway
roadblocks. Most of those who sought this authorization were
scientists and military support personnel whose job required that they
work near ground zero. Except for a group of two military men and
three civilians who went to ground zero on 16 and 17 July and a group
of two civilians who approached as close as 90 meters on 18 July, the
reentry personnel came no closer than 180 meters to ground zero. Of
these personnel, the individual who received the highest exposure
during the three days was an Army sergeant who received 15 roentgens.
During the same period, two civilians received 10 roentgens and 7.5
roentgens, respectively. All other personnel received exposures of 5
roentgens or less (1; 3).

After the "Going-In Board" was disbanded on 19 July, permission to
enter the ground zero area had to be obtained from Dr. Bainbridge or
one of his deputies. Many scientists entered the ground zero area
after 19 July to retrieve instruments or to perform experiments. The
population of the TRINITY test site was diminishing, however, as the
emphasis shifted to preparing the devices that were to be dropped on
Japan (1).

On 23 July, a week after the shot, chain barricades with prominent
signs warning against trespassing were placed 910 meters north, south,
and west of ground zero. These barricades were supplemented with two