PLUTONIUM-BEARING PARTICLES FROM FUEL REPROCESSING 135 



Of the major crustal elements listed in Table 6, silicon and iron were the most 

 ubiquitous, being found in most particles. The enrichment-factor distribution for these 

 elements, however, does not fall within the log-normal distribution for crustal material. 

 For the enrichment factors of an element to match the log-normal distribution of crustal 

 material in aerosols, there should be about 16% of the enrichment factors of less than one 

 geometric standard deviation, 68% within one geometric standard deviation of the mean, 

 and another 16% above one geometric standard deviation. This lack of conformity may 

 result from the low values for the geometric standard deviations of the enrichment factors 

 for these elements in aerosols. 



Only the enrichment factors for sodium and chlorine fall within the log-normal 

 distribution for crustal material. This may be due to the relatively high solubiUty of 

 compounds of these elements and, in the case of chlorine, the high value for the 

 geometric standard deviation. 



Particles from System I contain a greater variety of elements than those from 

 System II, and thus all but four elements are contained on a higher proportion of 

 particles from System I than from System II. The most striking example was nickel. 

 Although 56% of the particles from System I contained nickel, only 9% of those in 

 System II did. The major crustal elements (those in Table A.l comprising 0.4% or more 

 of crustal material) are contained on over half the particles from System I and, except for 

 magnesium in particles from sampling points C and D and titanium, are also contained on 

 over half the particles from System II. Some of the minor elements (those comprising 

 0.1% or less of crustal material) are present in over half the particles, viz, nickel, 

 chromium, and zinc in particles from System I and sulfur, chromium, and zinc in particles 

 from samphng point B of System II. The chromium and nickel may have come from the 

 304L stainless-steel alloy of cabinets and exhaust ducts or the Hastelloy*-C alloy in the 

 wet cabinets. However, few of the particles contained the proper ratio of chromium to 

 nickel found in either alloy. Also, \{ Hastelloy-C contributed the nickel in the particles, 

 some molybdenum should also have been detected. 



Of the elements that are present on less than 10% of the particles, all but copper on 

 particles from System II have high enrichment factors. This indicates that the minor 

 constituents of crustal material are not uniformly distributed among particles but are 

 concentrated on a few particles where they represent a major constituent. 



The plutonium-bearing particles were larger than natural aerosol particles collected at 

 relatively low altitude (<2.3 km), as shown in Fig. 7. Particles collected from sampling 

 points A and B of System II were larger than those from System I, with geometric mean 

 diameters two or three times as great as those of particles from other locations. 



The size of about 95% of the plutonium-bearing particles ranges between 0.4 and 37 

 jum in diameter. Morrow (1964) estimated that with normal respiration all particles in a 

 monodispersed aerosol of unit-density spheres 37 /im in diameter will be deposited in the 

 nasopharyngeal region of the respiratory tract. [With larger (>37 jum) particles the 

 fraction deposited rapidly decreases.] As the diameter decreases, the fraction deposited in 

 the respiratory tract decreases until a minimum of 20% deposition is reached for particles 

 that are around 0.1 to 0.2 iin\ in diameter, where the particles tend to remain airborne. 

 As the diameters decrease below 37 jum, a larger fraction is deposited in the 

 tracheobronchial region until 70% of the particles 5 jum in diameter are deposited in the 

 tracheobronchial region and only 5% in the nasopharyngeal and 5% in the alveolar 



*Trademark of Cabot Corporation, Boston, Mass. 



