WORLDWIDE FALLOUT 73 



5.0 



1.0 



a. 

 o 



Q. 

 CO 



0.1 



0.01 



O , Southern hemisphere, HASL 

 A , Northern hemisphere, HASL 

 hemisphere, Battelle 



1962 1963 1964 1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 



YEAR 



Fig. 8 Average yearly activity ^ ^ ^ Pu/ 



2 3 9.240 



Pu ratios in surface air. 



Stratospheric origin indicates that the transfer involved movement into the northern 

 stratosphere and then to the troposphere. The hemispheric yearly averages compared with 

 the yearly average at Richland, Wash., are shown in Fig. 8. Concentrations of SNAP-9A 

 ^^^Pu in the northern hemisphere and at Ricliland have decreased rapidly since 1968 and 

 1969, respectively. 



Similar changes in ground-level air concentrations were observed at other locations in 

 the northern and southern hemispheres (Hardy, 1976). These results indicate that the 

 stratospheric debris injected into the high stratosphere may not produce high concentra- 

 tions of the debris in ground-level air until 2 yr later. These ground-level concentrations 

 may in some regions remain nearly constant for about 2 yr before they begin to decrease. 



Although not formed direcdy in the nuclear weapons detonation, considerable 

 amounts of ■^'' 'Am are present in fallout debris. This, of course, results from the decay of 



24 1 



2 39 ,240i 



Pu. On the basis of the amount of ^•^'''^'♦"Pu in the atmosphere and the ratio of 

 ^^^Pu to '"^'Pu observed in the Mike test, one can calculate the ^"^ 'Am as a function of 

 time in the atmosphere. The ^^' Pu and the '^'''Am ratios are plotted in Fig. 9 together 

 with the observed concentrations of ^'^'Am as measured from samples taken at a 

 monitoring station in Richland, Wash. It is evident that the airborne concentrations are in 

 reasonably good agreement with those calculated. Also, the ratio of ^"^ 'Am to 2 3 9,2 4 Op^ 

 does increase, as would be expected, as the debris ages. On the basis of the yields of 

 transuranium elements, which were observed in the Mike tests, and the 2 3 9,2 4 Op^ 

 updated inventory established by the Environmental Measurements Laboratory (EML), 

 the total amounts of the other transuranium elements that have entered the atmosphere 

 can be estimated. These values are shown in Table 8. For isotopes of mass greater than 

 244, the total atmospheric injections are in the range of hundredths to tens of curies, and 

 the total alpha-decay activity of all the transuranium elements of mass greater than 241 is 

 only about 1% of the ^^''•'^"Pu. 



