136 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



regions. With still smaller particles, the fraction deposited in the tracheobronchial region 

 decreases until at 0.2 /um diameter only 10% is deposited in the tracheobronchial and 10% 

 in the alveolar regions. For dust particles with a density of around 2.5, this distribution 

 will be shifted toward smaller diameters so that 100% deposition in the nasopharyngeal 

 region occurs around 5 nm. 



Particles from all parts of System II also contained, on the average, more plutonium 

 per particle than those from System I. As shown in Table 1 1 , the geometric mean number 

 of tracks per particle from unfiltered wet-cabinet air was just over three for both fifth- 

 and sixth-level cabinets (averaging about 0.08 fCi per particle), whereas that for filtered 

 wet-cabinet air was about one-third of this, or almost the same for room air (averaging 

 about 0.02 fCi/particle). 



A comparison of the mean diameters of particles collected from different sampling 

 points, given in Table 9, with the mean number of fission-fragment tracks for particles 

 from the same location, given in Table 11, indicates a possible relationship between 

 particle size and plutonium content. Correlation coefficients between the cube of the 

 particle diameter and the number of fission-fragment tracks from each particle from 

 sampHng points B, C, and D were calculated. These are given in Table 12. These 

 coefficients differ significantly from that expected from a random sample from a 

 population of paired variables having a correlation coefficient of zero. Thus, even though 



TABLE 12 Correlation and Coefficient of Alienation for the Cube of the 



Diameter and the Number of Fission-Fragment Tracks for 



Particles from Sampling Points B, C, and D of System II 



Sampling Number of Correlation 

 point particles coefficient 



the points on a plot of particle diameter cubed vs. number of fission-fragment tracks 

 appear scattered, there is a significant correlation between the quantity of plutonium in 

 particles collected from sampling points B. C, and D in System 11 and the particle volume. 

 (Tracks with particles collected at other sampling points, where only ^"'^Pu could be 

 found, were counted but not recorded for each particle. Only where a ratio of 

 alpha-particle to fission-fragment tracks was needed to distinguish plutonium-bearing 

 particles from those having other fissionable materials were the track counts recorded.) 



Summary and Conclusions 



The elemental compositions, sizes, structures, and ^"'^Pu contents were determined tor 

 558 plutonium-bearing particles collected from various locations in the exhaust t rom a 

 reactor fuel reprocessing facility. Airborne particles were collected on polycarbonate 

 membrane filters. Particles containing ^^^Pu were identified by fission-fragment and 

 alpha-particle tracks produced by them in a polycarbonate film with a nuclear-track- 

 emulsion coating. When located, the amount of "^^^Pu in each particle was determined by 



