PLUTONIUM-BEARING PARTICLES FROM FUEL REPROCESSING 133 



5 10 20 30 40 50 60 70 80 90 95 

 PARTICLES HAVING ^T TRACKS, % 



98 99 



Fig. 8 Distribution of the number of tracks per particle for particles collected from 

 sampling points A, B, C, and D in System II. 



Discussion 



The most abundant elements in average crustal rock (and soil) are oxygen (46.60%), 

 silicon (27.72%), aluminum (8.13%), iron (5.00%), calcium (3.63%), sodium (2.83%), 

 potassium (2.59%), magnesium (2.09%), and titanium (0.44%) (Mason. 1966). Except for 

 oxygen, which was not detected by electron-microprobe analyses, these elements are also 

 found in most inorganic particles (Tables 6 and A.l). This supports the idea that most 

 plutonium-bearing particles are airborne crustal material to which minute quantities of 

 plutonium have become attached. 



Of particular interest is the quantity of "'^''Pu contained on these particles. One 

 femtocurie o\' ""'''Pu irradiated under the conditions described here should produce 41 

 fission-fragment tracks. The mmmuim detection limit tor electron-microprobe analysis of 

 plutt)nium is abt)ut 0.2 pg. or about 10 fCi, of ^^^Pu (Sanders, 1976), which is equivalent 

 to 410 fission-fragment tracks. Because of this relatively low sensitivity of electron- 

 microprobe analysis, plutonium could be detected by this method in only 1 of the 558 

 particles selected for analysis, even though all the particles produced tlssion-fragment 

 tracks. This single particle was a small, l-/;m-diameter particle collected from unfiltered 

 wel-cabinel exhaust. It contained 73% PUO2 by weight (equivalent to 170 fCi of ^^^Pu) 

 in ct)mbination with Fe203 and mica. 



