192 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



Aliquot size, g 1 10 25 50 100 



N 20 20 20 20 20 



Median 1.56 1.71 1.56 1.82 1.91 



Mean 1.93 1.82 1.80 1.84 1.92 

 Standard deviation 



of mean 0.34 0.11 0.12 0.05 0.04 



Fig. 3 Americium concentrations in soil aliquots of different sizes from nuclear site 

 201, Nevada Test Site, 



aliquots is much larger (standard error, 0.34) than that of the 10-g aUquots (standard 

 error, 0.11). The observed particulate nature of environmental transuranic element 

 concentrations suggests a hypothesis for tliis phenomenon. Assume that the americium 

 occurs as particles that are randomly dispersed throughout the soil. For a large (100-g) 

 aliquot size in which the probability of sampling a particle is high, the observed 

 concentrations will probably be reasonably consistent. However, as the aliquot size 

 decreases, the probability of getting a particle also decreases. This tends to violate the 

 homogeneous dispersal assumption. Tlie result is that the observed concentrations will 

 tend to show more variability, as evidenced in the extreme case by the 1-g aliquots. 



The data show a positive skewness to high values which is most pronounced for the 

 smaller aliquot sizes. This behavior is consistent with the hypothesis of the previous 

 paragraph, in which the assumptions are similar to the axioms that generate the Poisson 



