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with care in order to avoid cross contamination. The tissue gamma activity was measured in a sodium-iodide crystal scintillation counter.
A diagram of the flow system for the experimental apparatus for exposing the animals to the various aerosols is shown in Fig. 1. The
equipment consisted of:
(1) an aerosol generator, (2) the animal expo-
sure chamber, (3) millipore filter sample collectors (for determining
size and concentration of the particle) and (4) supporting equipment (flow
meters, pressure controls, pump, filters, etc.).
The animal exposure
chamber and the method of exposing mice to the radioactive aerosol is
illustrated in Fig. 2. The mice are positioned in such a manner as to
maximize inhalation and to minimize the possibility of ingestion of the
aerosol by the mice.
Aerosol Preparation
The dry particle aerosols were prepared by adding Sr or La chlorides
to suspensions of previously prepared particles. These particles were
of kaolin of less than 5,u in diameter. The particles and fission products
were evaporated to dryness ina ball mill. The particles were ground to
fineness and placed in the elutriator, as described below. The aerosol
to which the animals were exposed consisted of particles having a maximum diameter of 10m. About 60 percent of the particles had a diameter
in the range of 1 to 3a.
the particles.
The Sr and La were adsorbed on the surface of
The ionic SrClz aerosol was prepared by dissolving Sr85Cl2 in sea
water and aspirating it as a liquid aerosol. The mean particle diameter
was 1.8a1. This method of gene rating the liquid aerosol and measuring
its size was previously described. 5,
Aerosol Generation
The animal inhalation apparatus consisted of a Roller particle-size
analyzer coupled to the mouse exposure chamber. The Roller apparatus
analyzes a powder sample by successively removing and collecting larger
particle-size fractions of the powder by air elutriation. Sa study of the
operating characteristics of the Roller particle-size analyzer has shown
that for small particle sizes the rate of separation of material during the
first three hours of operation remains relatively constant. 9,10, phus,
the Roller separator is a suitable instrument for use as an aerosol generator in animal inhalation studies.
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