PLUTONIUM-BEARING PARTICLES FROM FUEL REPROCESSING 139 



as various marine locations. As a framework from which to view much of the order in 

 atmospheric aerosols, Rahn used the concept of aerosol-crust enrichment factors for the 

 elements. This concept has been applied to analyzing data collected in this study to 

 provide for (l)the intercomparison of the compositions of plutonium-bearing particles 

 with atmospheric aerosols compiled by Rahn and (2) the intracomparison among particles 

 collected from different sampling points. 



Microprobe Analyses of Particles 



For comparison, results of microprobe analyses must be expressed as elemental ratios 

 because not all elements that may be present in an aerosol are detected by microprobe 

 analysis. The microprobe used in this study is quantitative only for elements with atomic 

 numbers greater than 10. It is only semiquantitative for oxygen (the most-abundant 

 element in crustal material) as well as for other major elements of low atomic number, 

 such as hydrogen, fluorine, and carbon. Atmospheric aerosols are known to contain, in 

 addition to elements and oxides, carbonaceous material, such as sooty carbon and 

 organics, and water-soluble ionic material, such as sulfate, nitrate, and ammonium ions. 

 Thus elemental weight percents, normalized to 100 on the basis of the elements detected, 

 cannot be compared. Even the addition of a hypothetical oxygen concentration, 

 calculated on the supposition that all elements are present as oxides of known valence, 

 will still not account for the organic fraction of particles. However, a ratio of the 

 concentrations of one element to another will normally be relatively unaffected by the 

 concentrations of other elements that may be present and thus can be used for 

 comparisons even when a complete analysis of all the elements in an aerosol or single 

 particle is not available. 



Enrichment Factors 



A dimensionless ratio of elemental concentrations, called the enrichment factor, has been 

 defined as 



EF(X) = ^-^^^^^iH£l£l (A.l) 



where EF(X) is the enrichment factor of element X in an aerosol relative to some source 

 material and X/Ref is the ratio of the concentration of element X to the concentration of 

 the reference element, Ref, in both the aerosol and the source material. 



Source Material 



Elemental ratios in aerosols or in single particles are nonnalized by dividing them by 

 ratios of the same elements in a standard source material to obtain the enrichment 

 factors. If a particle is composed of the same material as the source, the enrichment 

 factor will be 1.00 for all elements. If the ratio of an element to the reference element is 

 greater or less than the same ratio in the source material, the enrichment factors will be 

 greater or less than 1.00, and the particle is said to be either enriched or depleted, 

 respectively, in that element. 



The most commonly used crustal source material for continental enrichment-factor 

 calculations is globally averaged crustal rock. (For marine enrichment-factor calculations, 

 sea salt is used.) The selection of rock may seem strange because there is little doubt that 



