0018933 of the radionuclide composition of local fallout as determined from the rocket samples. The influence of the environment on fallout partition was to be investigated by participation in events over land and water surfaces, 1.3.2 Rocket Samplingof 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-verti- cal flight path requirement necessitates the use of sample collectors which are propelled by rockets. ; 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 ac- tion of aerodynamic forces 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, aren) FRE SAN BAe: 35 ~~ 35