analyzed here to perform such an analysis. 3.9 RADIOACTIVE PARTICIE SIZE ANALYSIS The dried samples from all trays of each collector were combined, weighed, and then sieved through a 44-91: sieve. The weight of each fraction was determined and a weighed portion of each fraction was used for radioautographye These fractions were washed from the weighing dishes with tolusne onto the backside of Eastman NTB 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 (Fige 3.29). emulsicn and a J=y thick backing. The NTB film has a 10—p thick The radioautogranhs 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 developed 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 a 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 illumination. The particle images we-e pro jected at a mgnification of 1000X. Radioactive particles cnly were measured. The limitations of the optical microscope precluded the observation of particles below abcut 1 pe PARTICLES _ BACKING CANADA BALSAM t — | eMULsion PREPARATION POSITION DEVELOPING SOLUTION EWULsion { BACKING ' CANADA PARTICLES BALSAM DEVELOPING ANO EXAMINATION Fige 3029 POSITION Preparation of Particle Medium; Developing and Examination Position of Stripping Film 85