PLUTONIUM-BEARING PARTICLES FROM FUEL REPROCESSING 113 



container in the water bath. The molten emulsion is tested by dipping a clean glass 

 microscope sUde into it and exarnining the coat on the glass under a safeHght to 

 determine whether bubbles are present. If bubbles are present, they are scooped from the 

 surface of the molten emulsion with a porcelain spoon. 



The polycarbonate films are coated with emulsion by holding the supports containing 

 the films vertically by one corner and dipping them into the clear molten emulsion for 

 about 1 sec. The films are kept vertical until the excess emulsion has drained off. The 

 coated films are then placed horizontally in a TH-Junior temperature-humidity test 

 chamber* that is maintained at 28°C and about 80% relative humidity until the emulsion 

 cools and gels (about 30 min). 



Exposure 



The polycarbonate films are exposed for 1 week before being developed to determine the 

 alpha-particle emission rate for each aerosol particle. The films are stored in spun 

 aluminum Desicoolersf containing 60 g of indicating Drierite during this exposure of the 

 emulsion to the particles. The Desicoolers are sealed with black adhesive tape and stored 

 in a refrigerator between 4 and 5°C for the duration of the exposure. 



Emulsion Processing 



At the end of the exposure period, the alpha-parficle tracks in the emulsion are 

 developed, and all substances other than tracks are removed from the emulsion. The 

 emulsion is developed in a 1:1 solution of DektolJ developer for 3 min at 17 C 

 (Eastman Kodak Company, 1976; Boyd, 1955; Kopriwa and Leblond, 1962). 



Immediately following development the film is rinsed in 28% (vol. /vol.) acetic acid 

 for 10 sec. The high acid concentrafion is used to prevent reticulation of the emulsion 

 and its separation from the supporting polycarbonate film. 



The rinsed emulsion is fixed by placing it for 5 min in a 1 : 3 dilution of Kodak rapid 

 fixer concentrate § containing 2.8% (vol. /vol.) hardener concentrate. 



A batch process is used to wash all chemicals except the metallic silver from the 

 emulsion. The emulsion-covered film is placed in distilled water, and the chemicals in the 

 emulsion and wash water are allowed to approach equilibrium for 2 min. The emulsion is 

 then placed in a second container of distilled water while the water in the first container 

 is being changed. This process is repeated a total of eight times. After the water wash, the 

 emulsion-coated polycarbonate films are placed in racks and allowed to dry in a dust-free 

 atmosphere. 



Track Counting 



The film is prepared for track counting by placing the acrylic support on a 50-mm-square, 

 1.0-mm-thick polycarbonate block. 



Particles with tracks are located under a Bausch and Lomb zoom stereomicroscope by 

 using transmitted light and a magnificafion of 105 X. Each particle with tracks is circled 

 with a felt-tip marking pen. After a particle has been marked, the support and block 

 holding the film are moved to a Zeiss photomicroscope where the fission-fragment and 



*Manufactured by Tenney Engineering, Inc., Union, New Jersey. 



■fTrademark of Fisher Scientific Company. 



if Trademark of Eastman Kodak Company. 



§ Kodak Photographic Products catalog numbers 146 4106 or 146 4114. 



