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ABSTRACT
An evaluation of the acute inhalation hazard from radioactive fall-out materials has been
made by analysis of results from animal exposures during field operations and from controlled
inhalation studies in the taboratory,
Rabbits and rats have been subjected to controlled inhalation exposures to dusts prepared
by micropulverizing fused insoluble radivactive siliceous matertal obtained from Area 3 at the
Nevada Test Site, Operation Upshot-Knothole. In these laboratory studies, field conditions
were simulated in respect to duration of exposure, particle-size distribution, and levels of
air-borne radioactivity involved. The relation between particle size, dust concentration, and
duration of exposures to initial deposition in the lungs and gastrointestinal tract has been determined. In addition, the rates of removal have been measured. The laboratory studies dem-
onstrate two important phystological-safety factors against the retention of dangerous quantities of inhaled particulate materials, These are, first, the filtration mechanism of the upper
respiratory passages which limits pulmonary retention to particles of small size (below 5.0 y),
and, second, the normal clearance mechanisms of the upper and lower lung passages which remove initially deposited large and smal! particles at rapid rates.
entirely negative. Urine specimens obtained during the first day following detonation contained
minute but measurable amounts of soluble radioactive material which had a relatively short
half life (i to 2 days). Lung specimens had no detectable radioactivity when measured 6 to 21
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The results from exposing several groups of rabbits to fall-out material (by inhalation
only) at stations located along two arcs, 7 and 106 miles from a tower detonation, are almost
days later; however, samples of intestine from the same animals still had measurable levels
of beta activity.
The total integrated internal radiation exposure could be expressed in millirep, even at
the close stations, where the integrated external gamma-ray exposure was found to be 14 to
32 r, At the 106-mile stations, no measurable radioactivity was present in specimens of lung
or urine; however, the levels of radioactivity in intestine samples were either negative or
several times lower than those found in animals at the near stations. The external gamma-ray
dose was less than 4.0 r.
From careful consideration of numerous pertinent physical and physiological factors and
from analysis of field and laboratory investigations, it is evident that there is no apparent
situation in nuclear warfare where, during the first few days after the detonation, one could
inhale sufficient radioactive material to induce a serious radiation injury to lungs or intestines
without stmultaneously being subjected to supralethal doses of external beta-gamma radtation.