PLUTONIUM-BEARING PARTICLES FROM FUEL REPROCESSING Ul 

 TABLE 2 Atom Percents in Six Typical Mixtures of Uranium 



TABLE 3 Atom Percents in Three Typical 

 Mixtures of Plutonium 



Nuclide 



■Pu 5 X 10"" 1 X 10- 



'Pu 0.0115 2.9 80.3 



'Pu 93.6 39.6 15.87 



From Tables 4 and 5 the mean ratio (alpha-particle-to-fission-fragment tracks) for 

 low-irradiation plutonium is 9.1 X 10"^ and that t\)r highly enriched uranium is 

 1.8 X 10~^ Thus '^^Pu can clearly be distinguished from ^^^U by this procedure if 

 there is a sufficient number o{ tracks. However, these ratios are 1.7 and 2.5 times the 

 theoretical ratios given in Table 1. For highly enriched uranium, all alpha-particle tracks 

 were observed as single tracks only, some of which may have been due to background 

 radiation; this would explain the higlier mean ratio for uranium. With plutonium the 

 higlier observed ratios are probably due to the geometry of the media in which the tracks 

 are formed. 



Quantitative Radiographic Analysis 



Alpha-particle and fission-fragment track counts will provide not only a ratio from which 

 the fissionable material carried on the particles can be identified but also an estimate of 

 the quantity of the radioactive nuclides present. One femtocurie (1 fCi = 10' '^ Ci) of 

 ^^^Pu will produce about 22 alpha particles in a week, and, when irradiated with a 

 fluence of 8.64 x 10'"* thermal neutrons/cm', it will produce about 40 fission fragments. 

 In a mixture of low-irradiation plutonium, the number of fission fragments produced will 

 be increased to 53 with between 28 and 33 alpha particles, depending on the age of the 

 mixture. Only about half of these particles will produce tracks; yet this radiographic 

 technique is much more sensitive than electron-microprobe analysis, which is not sensitive 

 to less than 10 fCi (Sanders. 1976). 



