1 08 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



then covered with a thin collodion membrane and a gelatin bonding medium. A square of 

 Kodak autoradiographic permeable base film was then floated onto the surface of the 

 gelatin with the sensitive emulsion upward. After exposure and development, the 

 Millipore filter was made transparent with a collodion solution. 



About the same time Moss, Hyatt, and Schulte (1961) developed a simpler method of 

 relating the particles with the tracks they produce. These investigators collected airborne 

 plutonium samples on membrane filters in a processing plant at Los Alamos Scientific 

 Laboratory wdiere plutonium metal was handled in glove boxes. The membrane filters 

 were pressed on a glass slide covered with nuclear track emulsion with the contaminated 

 side in contact with the emulsion. When excess water was blotted from the slide, the 

 emulsion, which had been softened by submerging it in water for several minutes before 

 using it, became tacky. The filter was then separated from the emulsion, and the particles 

 were left embedded in the emulsion. 



To calculate the particle size. Moss, Hyatt, and Schulte (1961) assumed that the 

 particles were spheres of pure ^^^PuOa. However, some particles appeared larger than 

 calculated, which led the group to speculate that, "when plutonium dust settles on 

 surfaces and is resuspended during cleaning, the resuspended particles are much larger and 

 are only partly composed of plutonium." 



Andersen (1964) made a particle size study ot plutonium aerosols in employee work 

 areas at Hanford Laboratories in 1963. Here samples were collected on membrane filters 

 and HoUingsworth and Vose type 70 filter paper. The filters were contact exposed to 

 nuclear track emulsions by a method similar to that of Leary (1951). The filters were 

 mounted in X-ray exposure holders altered so that the nuclear track film could be 

 positioned reproducibly. These and the use of a microscope-stage micrometer permitted 

 sufficient reproducibility in film location that a particle in question could be readily 

 relocated. He found the plutonium particles to be small with a geometric mean diameter 

 less than 0.04 to 0.1 jum. He assumed that plutonium was not attached to dust particles 

 since copious quantities of plutonium were generally involved during particle formation 

 and the effect of foreign particles was not extensive. 



An autoradiographic technique for the location and examination of alpha active dust 

 particles collected on glass-fiber paper, developed by Stevens (1963), was used by 

 Sherwood and Stevens (1963; 1965) to analyze laboratory air samples taken at the 

 Atomic Energy Research Establishment at Harwell, England, in 1963. Each filter was 

 mounted in an Araldite (epoxy resin) mixture, which renders the filter transparent, and 

 was covered with autoradiographic stripping film. After exposure and development, the 

 sample was viewed with a high-powered optical microscope. The particles that were 

 identified as radioactive by the alpha-particle tracks emanating from them were sized, and 

 their radioactivity was determined by counting the number of tracks. Stevens and 

 Sherwood found that relatively few of the particles collected were pure plutonium or 

 plutonium compounds. Most of the particles were large inert particles contaminated with 

 plutonium. 



As late as 1965 Kirchner (1966) used the contact-exposed method of Leary (1951) to 

 analyze air samples obtained from work areas in plutonium chemistry and fabrication 

 plants at Rocky Flats. Although this procedure did not permit examination of inert 

 particles, Kirchner beUeved that the autoradiographs indicated that agglomeration with 

 inert or other active particles was rare. He also believed that, despite good agreement in 

 the activity median diameters reported at Harwell (Sherwood and Stevens, 1965), lung 



