RADIATION PROTECTION AT PROJECT TRINITY
The TR-7 or Medical Group, shown in the figure 1-5 organizational
chart, was responsible for radiological safety at Project TRINITY.
Many of the physicians and scientists in the Medical Group had worked
with radioactive materials before and were trained in radiological
safety procedures. The Chief of the Medical Group supervised the
radiological safety operations and reported to the TRINITY director.
In addition to providing medical care to TRINITY personnel, this group
established radiological safety programs to:
o Minimize radiation exposure of personnel on the test site and in
offsite areas
o Provide monitors to conduct radiological surveys onsite and offsite
o Provide and maintain radiation detection instruments
o Provide protective clothing and equipment.
An exposure limit of 5 roentgens during a two-month period was
established. Personnel were provided with radiation detection
instruments to determine their exposures (1).
3.1 ORGANIZATION
The Medical Group consisted of physicians, scientists, and
administrators, as well as radiological monitors. Many of these
personnel were nonmilitary, but all worked on the Manhattan Project
under the administration of the Army Corps of Engineers Manhattan
Engineer District.
The Medical Group was divided into two monitoring groups, the Site
Monitoring Group, which was responsible for onsite monitoring, and the
Offsite Monitoring Group. Each reported to the Chief of the Medical
Group, and each communicated with the other during the monitoring
activities. In addition to these two groups, a small group of medical
technicians provided radiation detection instruments to Medical Group
personnel (1; 10).
3.2 SITE MONITORING GROUP
The Site Monitoring Group consisted of a chief monitor, three other
monitors, and several medical doctors. This group had the following
functions (1; 10):
o Conduct ground surveys of the test area and mark areas of
radioactivity
o Conduct surveys of the Base Camp and roads leading into the test
area
o Provide protective clothing and equipment, including film badges and
pocket dosimeters, to personnel
o Monitor all personnel for radioactive contamination and provide for
their decontamination
o Maintain a record of radiation exposures received by personnel.
The Site Monitoring Group monitored the radiation exposures of
personnel in the test area. The time spent by personnel in radiation
areas was limited, and radiation detection instruments were provided
to permit continuous monitoring of exposure rates. In many cases, a
monitor from the Site Monitoring Group accompanied project personnel
into the test area to monitor exposure rates (1; 10).
Two members of the Site Monitoring Group, a monitor and a physician
with radiological safety training, were assigned to each shelter. The
supervising monitor was stationed at the Base Camp and was in radio
and telephone communication with all three shelters and the offsite
ground and aerial survey teams. Before any personnel were allowed to
leave the shelter areas, a radiological safety monitor and a military
policeman from each shelter advanced along the roads to Broadway to
check radiation levels. They wore respirators to prevent them from
inhaling radioactive material (1; 10).
Since it was expected that any dust from the cloud would fall on one
of the shelter areas within 30 minutes of the shot, plans had been
made to evacuate personnel as soon as the monitors completed their
initial survey. Because the cloud moved to the northeast, the south
shelter (the Control Point) was not completely evacuated, although
nonessential personnel were sent to the Base Camp. The west shelter
was emptied of all personnel except a searchlight crew spotlighting
the cloud as it moved away (1; 10).
Only at the north shelter did an emergency evacuation occur. About 12
minutes after the shot, a detection instrument indicated a rapid rise
in the radiation levels within the shelter. At the same time, a
remote ionization monitoring device detected a rapid increase in
radiation. Because of these two readings, all north shelter personnel
were immediately evacuated to the Base Camp, 25 kilometers to the
south. Film badges worn by personnel stationed at the north shelter,
however, showed no radiation exposure above the detectable level. It
was later discovered that the meter of the detector in the north
shelter had not retained its zero calibration setting, and radiation
at the north shelter had not reached levels high enough to result in
measurable exposures of the personnel who had been positioned there.
However, fallout activity was later detected in the north shelter
area, proof that part of the cloud did head in that direction. This
also explains why the monitoring device detected rising radiation
levels (1; 12).
After ascertaining that radiation levels along the roads leading from
the shelters to Broadway were within acceptable limits, the
radiological safety monitors and military police established
roadblocks at important intersections leading to ground zero. The
north shelter monitor and military police set up a post where the
North Shelter Road ran into Broadway. The west shelter monitor and a
military policeman blocked Vatican Road where it intersected Broadway.
The south shelter monitor and military police set up a roadblock where
Broadway intersected Pennsylvania Avenue (1).
The monitor assigned to Guard Post 4 surveyed the Mockingbird Gap area
to ensure that it was safe for the guards to return to their post.
This position controlled access to the McDonald Ranch Road, which led
directly to ground zero (1).
At 0540 hours, the chief monitor departed from the Base Camp with a
military policeman to monitor the entire length of Broadway. They
first checked the roadblock at Pennsylvania Avenue and Broadway. Next
they drove to the roadblock at Vatican Road and Broadway. Upon the
chief monitor's arrival, the west shelter monitor traveled about nine
kilometers west on Vatican Road to monitor Guard Post 1 so that the
military police could reoccupy the post. The monitoring excursion to
Guard Post 1 continued until the chief monitor had returned from Guard
Post 2, located 17 kilometers northwest of the Vatican Road roadblock
on Broadway (1; 18).
The chief monitor arrived at Guard Post 2 at about 0550 hours and
found the post empty. He then continued five kilometers north along
Broadway to the foxholes from which the military police had watched
the detonation. There he found the guards, the five radiological
safety monitors assigned to the evacuation detachment, and the
Commanding Officer of the evacuation detachment (1; 18).
The military policemen refused to return to Guard Post 2, insisting
that they had received orders over their two-way radio from the Base
Commander to evacuate their post and head for San Antonio, New Mexico,
a town 28 kilometers northwest of the Guard Post. The Base Commander
had noted that portions of the cloud were heading northwestward and,
fearing that fallout from the cloud would contaminate Guard Post 2,
had ordered the military police to evacuate. The chief monitor,
however, had found no significant radiation levels anywhere along the
northern part of Broadway nor around Guard Post 2. The Base Commander,
after being contacted by the chief monitor, drove to the foxholes and
ordered the guards to return to their post. This was the only
unplanned incident during the onsite monitoring (1).
After Guard Post 2 was reoccupied, the chief monitor returned 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 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).
3.3 OFFSITE MONITORING GROUP
Four two-man teams and one five-man team supervised by the chief
offsite monitor constituted the Offsite Monitoring Group. Before the
detonation, the four two-man teams established monitoring posts in
towns outside the test area. These towns were Nogal, Roswell, Fort
Sumner, and Socorro, all in New Mexico. The five-man team remained at
Guard Post 2 to assist in evacuation of nearby residences if the
TRINITY cloud drifted in that direction. These residences, the Fite
house and the homes in the town of Tokay, were 24 and 32 kilometers
northwest of ground zero, respectively. Since the cloud drifted to
the northeast, evacuation was not required. All offsite monitoring
teams were in radio or telephone contact with personnel at the Base
Camp (11).
Offsite monitoring teams in areas northeast of ground zero encountered
gamma readings ranging from 1.5 to 15 R/h two to four hours after the
detonation. Three hours after the detonation, surveys taken in
Bingham, New Mexico (located 30 kilometers northeast of ground zero)
found gamma intensities of about 1.5 R/h. Radiation readings at the
town of White, nine kilometers southeast of Bingham, were 6.5 R/h
three hours after the detonation and 2.5 R/h two hours later. Another
team monitoring in a canyon 11 kilometers east of Bingham found a
gamma intensity of about 15 R/h. Five hours later, the intensity had
decreased to 3.8 R/h. It was estimated that peak intensities of gamma
radiation from fallout on shot-day were about 7 R/h at an occupied
ranch house in this canyon area (1; 11; 19).
Monitoring teams resurveyed these towns about one month after the
TRINITY detonation. At Bingham, gamma readings of 0.003 R/h and
0.0001 R/h were found at ground level outdoors and at waist level
inside a building, respectively. At the town of White, the highest
outdoor gamma reading was 0.008 R/h. Inside a building, the highest
reading was 0.0005 R/h (11).
Surveys taken in the canyon area one month after the detonation
indicated that gamma intensities at ground level had decreased to
0.032 R/h. The occupied ranch house was also surveyed, both inside
and outside. The highest reading outdoors was 0.028 R/h, and the
highest reading indoors was 0.004 R/h (11; 19).
Monitoring was also conducted in offsite areas other than those to the
north and northeast of ground zero. Monitors found no radiation
readings above background levels (11).
Significant fallout from the TRINITY cloud did not reach the ground
within about 20 kilometers northeast of ground zero. From this point,
the fallout pattern extended out 160 kilometers and was 48 kilometers
wide. Gamma intensities up to 15 R/h were measured in this region
several hours after the detonation. One month later, intensities had
declined to 0.032 R/h or less (11).