5
EVENT AND DESCRIPTION OF EXPOSED GROUPS
1.2
carried out, nor was its operating condition
Whole Body Gamma Doses
known to be satisfactory under the emergency
condition prevailing at the time of use. For
these reasons the later readings, which were
higher than the early survey by an average of
50 percent ,when corrected to the same times,
Tue EstixaTep Vaces of external dose given
in Table 1.1 were calculated from readings of
radiation field survey instruments.* Averages
of a numberof dose rate measurements on each
island at a given time were used. The readings were taken in air, approximately three
feet nbove ground, several days after the inhab-
were used in computing the doses listed. The
instruments used for the later measurements
were calibrated just prior to the surveys.
390
wweewn= ORIGINAL SOURCE SPECTRUM
oomeme= «INFINITE PLANE,3IN AIR
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ENERGY (KEV)
Ficuge 1.2—Distribution of inherent energies of yamma radiation from mizcd
fission products, and histogram of degraded energics produced by Compton
scattering at level of infinitc plane 3 feet in air above uniformiy-distriduted
fission products flelid.
itants were evacuated.
Before this time, ade-
quate surveys with well calibrated instruments
had not been possible, although readings had
been taken with a single survey meter at the
time of evacuation. However, preliminary
calibration of this instrument had not been
*Army Navy catalog AN/PDR-39.
1.21
Characteristics of the Gamma Radiation
The fallout material, when deposited on the
ground, formed a large planar source of radia-
tion. The energy distribution of the radiation
reaching an exposed individual was influenced
by its passage through the intervening air. A
knowledge of the energy spectrum of the ra-