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fission products in the cloud.

If it can be established that the very early

distribution is normal and then departs from the normal pattern at a rate consistent
with the fallout interpretation, other separative forces might be considered un-

;

important.

123.2

Rocket Sampling of Clouds.

Experimental determination of the

distribution of activity within the cloud requires the collection of a group of

samples at different vertical distances along paths nearly parallel to the axis
and at various radial distances.

The almost-vertical flight path requirement

necessitates the use of sample collectors which are propelled by rocketse
The rockets used by the project had a rather complex structure (see
Chapter 2) but from the standpoint of particle collection their important features

were the sampling head and the electronic programmer.

The sampling head was

designed to separate the particles collected into two groups having falling rates
corresponding to local and world-wide fallout as already defined. The separation
was to be attained by the action of aerodynamicforces in the sampler similar in
effect to those experienced by particles falling through the atmosphere in the
gravitational field of the earth.

The function of the electronic programmer was to

open the head at predetermined positions in the flight path so that samples could
be collected from different portions of the cloud.

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