analyzed here to perform such an analysis.
309
RADIOACTIVE PARTICLE SIZE ANALYSIS
The dried samples from all trays of each collector were combined,
weighed, and then sieved through a 44-p sieve.
The weight of each
fraction was determined and a weighed portion of each fraction was
used for radioautography.e
These fractions were washed from the weighing dishes with
toluene onto the backside of Eastman NIB stripping film which was previously mounted on 4-in. plastic rings. The transfer was done in dim
light.
Canada balsam, which was added before the toluene evaporated
to form a uniform adhesive medium for the particles,did not interfere
with microscopic observation. The celluloid backing separated the
particles from the emulsion so that during processing the particle
medium was not disturbed (Figs 3029). The NTB film has a 10—p thick
emulsion and a 7p thick backing.
The radioautographs were exposed for the empirically determined
time of 15 hr for samples measuring 100,000 cpm, 25 hr for samples
counting 50,000 cpm, 60 hr for 25,000 cpm, etc. All exposures were
started 6 to 9 days after each shot.
The radioautographs were devel=-
oped in Eastman Kodak D~-19 Developer for 5 min at 20° C., then rinsed
and fixed for 10 min. All develcping operations were done without disturbing the particle medium. The particles were projected at 2 magnification of 1000 times with a micro-projector which consisted of a
Bausch and Lomb research microscope mounted on a micro=projector base
with carbon arc
a megnification
The limitations
particles below
illumination. The particle images we-e projected at
of 1000X. Radioactive particles cnly were measured.
of the optical microscope precluded the observation of
about 1 pe
PARTICLES
i=
BACKING
CANADA BALSAN
TZ) NT
emuLsion
PREPARATION POSITION
SOLUTION
EMULSION
BACKING |
CANADA
PARTICLES
HOLDER
BALSAM
DEVELOPING AND EXAMINATION POSITION
Fige 3029
Preparation of Particle Medium; Developing
and Examination Position of Stripping Film
85