r{i:sTiacT:^D 



18 



The factors exclusive of raclioactlve aecaj'" that -:.U3t be 

 considered in calculatine the rate of deconta. dnation after 

 the blasts are horis^ontal and vertical diffusion and current 

 direction and velocity, tiince all these factors are consid- 

 erably affected by weather, it is iapossible to uake a precise 

 prediction that will fit all cases. But barring a radical 

 change such as reversal of wind direction, the results should 

 be of the right order of magnitude . 'rhe present section is 

 based on the assiojription of a 10 knot jjNE wind at the time of 

 the tests. A further section will atteupt to describe wliat 

 would be likely to happen with certain other v/ind conditions. 



Assume that the explosion produces a voliuie of uniformly 

 contajainated v/ater with a radius of about 400 n. As horizon- 

 tal diffusion begins to operate, the size of the patch of con- 

 taminated water will increase, a gradient in concentration v/ill 

 develop from the center of the patch toward its periphery, and 

 the concentration in the center will decrease gradually. An 

 oceanographic theory developed by G. F. McEvi^en predicts that 

 the effect of diffusion will be as shovm in Table 7. 



Table 7. Reduction of contamination by horizontal 

 diffusion {% of initial concentration, 

 radioactive decay not included) 



Further dilution will take place by vertical diffusion, 

 and this effect can be determined from the measurements described 

 in the previous section. At the time of test Able, the contamina- 

 tion will be largely confined to the immediate, surface layer. 

 Assuming for purposes of calculation that at the end of three 

 minutes the radioactive products will have become uniformly 

 distributed through the upper 2.5 m. , then further dilution of 

 this surface, layer is expected to take place according to the 

 figures in Table 8. 



The patch of contaminated water will be carried V/SW from 

 the target area at a rate of about 0.3 knot. The contaminated 

 water that is diffused down into the bottom layer will be car- 

 ried back toward the target area. This removal of contaminated 



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