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