-
C.
(
sealed at all other times,
Sampling at the lower levels of ground to
40,000 feet was by means of air samples compressed into steel bottles
and carried in aircraft.
2.2
Sampling
Sampling by balloon takes place in two stages.
In order to effect
a high percentage of recovered collections on impact with the ground,
it is necessary to transfer the sample to a much stronger and smaller
bag.
This is done on the descent between altitudes of 30,000 and 3000
feet.
It will be appreciated that losses of both water vapor condensed
on the walls of the polyethylene bag and air not completely transferred
can occur at this stage.
The second sampling occurs when the air is pumped out of the impact
bag for use on other programs.
A sample of the water vapor is frozen
out of the air prior to entering the gas compressors,
2.3
Analysis
\
The recovered sample of water is split into two fractions.
concentration of deuterium is measured in one fraction;
The
the concentra-
tion of deuterium in the original tracer water hed been previously
measured.
Hydrogen gas is obtained from the other fraction by reduction
over magnesium and the tritium cc'nted in this hydrogen sauple, using a
geiger ccunter in a "cave" with enticoincidence circuitry.
In general,
the counting is no problem because the majority of the samples have a
counting rate an order of magnitude, at least, greater than beckground.
3.
43.1
COMPUTATION OF TRITIUM CONCENTRATION
Tritium
Provided no unknown @sount of tritium, deuterium or hydrogen is