oa ctivity within the mushroom. Quantitative data on the activity associated with particles
retferent size groups is also needed for estimation of the partition of the weapon bewean local and worldwide fallout. Project 2.8 was established to attempt to obtain such
information from certain shots during Operation Hardtack.
It was planned to explore the cloud
structure by means of air sampling rockets and to use both the rocket samples and aircraft
sampies collected from the cloud with the UCRL coincident sampler for determination of the
fallout partition. Other aircraft flying at 1,000 feet were scheduled to collect fallout samples
to be used for the determination of the effect of particle size on fractionation and for corrobora-
tion ofttre radionuclide composition of local fallout as determined from the rocket samples.
The influence of the environment on fallout partitlon was to be Lnvestigated by participation in
events over land and water surfaces.
The basic hypothesis on which the determination of fallout partition by the measurement of
relative enrichment is based is that the increase of a volatile material with respect to a refrac-
tory material, e.g., Kr°* with respect to Mo", occurs principally as a result of fallout of the
refractory matertal, i.e., the only force producing separation is gravitation.
{f this hypothesis
is correct, then the Mo”left in the cloud region sampled compared to the Krmay be inter-
preted as the fraction of refractory debris that will be distributed in worldwide fallout.
fraction (y) is given by
This
_ (R88) &
~ [R™(88)}¢
where the subscripts E and C refer to the explosion and the cloud, respectively.
If, however, other forces operate on the particles (particularly centrifugal forces that exist
a red@fring the initial phase of cloud rise or turbulent forces that may exist for several hours as
gult of temperature inequalities), the possibility exists that separation of gasses or small particles from large particles may occur without requiring real fallout of refractory material. It is
also possible that separation of the more volatile products from the less volatile may occur in
that gas phase as a function of altitude in the cloud without requiring separation of large particles
from small particles or particles from permanent gases. If these processes occur, even a large
enrichment of volatile material near the top of the cloud would not necessarily be attributable
principally to fallout.
To help determine whether these alternative processes are important, it ls considered nec-
essary to obtain very early data for R-values of relatively volatile 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 unimportant.
1.3.2 Rocket Sampling of Clouds. Experimental determination of the distribution of activity
within the cloud required 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 necessitated the use of sample collectors that were propelled by rockets.
The rockets used by the project had a rather complex structure (Chapter 2), but from the
standpoint of particle collection their important features were the sampling head and the electronic programer. The sampling head was designed to separate the particles collected into
two groups having falling rates corresponding to local and worldwide fallout as already defined.
The separation was to be attained by the action of aerodynamic forces in the sampler similar
in effect to those experienced by particles falling through the atmospherein the gravitational
field of the earth. The function of the electronic programer was to open the head at predetermined positions in the flight path so that samples could be collected from different portions of
the cloud.
°
It was planned to fire 18 rockets on each Shot at about H+10 minutes from launching plat-
forms spaced at various distances from ground zero.
Two rockets were to be fired along each
trajectory, one programmed to collect a sample fromthe base to the top of the debris and the
other to collect from the top half of the cloud only.
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