136
LOYSEN
ever, the sampler was not specifically designed with such collection as
an objective.
In the first five tests, the electron-microscope grids were taped
to the clean aluminum surface. In the last two tests, the uncoated strip
was eliminated,
and the grids were attached with a small amount of
the colloidal graphite suspension. The number of grids mounted in the
COLLECTING CYLINDERS
EXIT VALVE
ENTRANCE VALVE \
CORONA-WIRE SUPPORT
CORONA-WIRE
Fig. 1—ComponentsMie! Electronics Corporation electrostaticprec tpitatorgorees,-
sampler ranged.iTeh
F oe
3 ae first test to as many as 25 in subsequent
tests. Precoated:sepitis5wel
tained@rom a vaporonclley
Before the ‘gridéwereSmounted, ‘they were spot-ch
clean-
liness in an electron gaiéFscope and were found to be clean.fpwever,
in recent, more thorough examinations of new carbon-coatéd grids
obtained from the same source, particles have been detected. This finding raised a question régarding differentiation between stratospheric
particles and background contamination on the grids. Radioautographs
of sections of the uncoated aluminum strips on which the grids were
mounted definitely established the fact that radioactive particles were
collected. Figure 2 is a typical radioautograph on nuclear-track emulsion showing the presence of both alpha and beta radioactivity. The
approximate concentration of these particles as determined from the
radioautographs is 10‘ particles per cubic foot. The concentration of
all particles as determined from the photomicrographs is also about
10‘ particles per cubic foot. Therefore it appears that the particles
that were counted were both stratospheric and radioactive.
After the grids were mounted on thé,glyminum liner, the ends of
the electrostatic precipitator were covered and sealed with polyethylene bags until launch time. The precipitator wa@quipped with butter-
fly valves at each end to prevent the entry éf ar frggnthe, ime that
the balloon was launched until the sampling.altitutle was r
ed..The
valves did not provide an airtight seal, haw@ver. At the end of the 3- to
4-hr sampling period at a fixed altitude, ‘the butterfly valves were
closed, and the sampling unit was released from the balloon to return