IS TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



notable exception to this trend was the Antarctica sample (70°S), where 1966 

 represented the maximum concentration. It has been theorized that air movement above 

 21 km involves an ascent of air over the summer pole, a mesospheric meridional flow 

 from the summer to the winter hemisphere, and a descent of air over the winter pole. 

 This, coupled with the residence half-time at this altitude of 6 months (Thomas et al., 

 1970) and reentry burnup of the SNAP-9A generator occurring at 46 km in the southern 

 hemisphere over the Indian Ocean, produced a condition where the meridional flow from 

 the northern hemisphere to the southern hemisphere had either begun or was about to 

 begin. All these factors resulted in a disproportionation of ^■^^Pu deposition, 73% in the 

 southern hemisphere and 27% in the northern hemisphere, and could have transferred 

 debris over the south pole, resulting in a more rapid movement downward at the pole 

 than at other southern or northern latitudes. Whatever the mechanism is for distribution 

 of SNAP-9A debris througliout the hemisphere, these data show that debris injected in 

 April 1964 at 46 km altitude reached a maximum in ground-level air about 2 or 3 yr later, 

 depending on the latitude, and by 1971 it was largely depleted from the atmosphere. 



From October 1970 until January 1971, soils were collected by EML (Thomas and 

 Perkins, 1974) from undisturbed areas at 65 sites around the world to determine the 

 total deposition of plutonium. Each sample consisted of ten 8.9-cm-diameter cores taken 

 to 30-cm depth, which represented a surface area of 622 cm^. The measured ^^*Pu 

 included that from weapons testing plus the SNAP -9A contribution. The ■^^^'^'*°Pu was 

 assumed to be entirely derived from weapons testing. The EML estimated the weapons 

 ^^^Pu contribution by multiplying the 239,240p|j y^^gg ^y 0.024, their average weapons 

 238p^/239,240py ratio fouud for six soils collected before fallout from the SNAP-9A 

 (Krey et al., 1976). These soils were selected to cover a range of latitudes from 71°N to 

 35°S. The SNAP-9A ^^^Pu was simply the difference between the total measured ^^^Pu 

 and the weapons ^•^^Pu. The EML deposition sites were grouped into ten-degree latitude 

 bands and the deposition values averaged as shown in Table 9. The average activities of 

 ^^*Pu per square kilometer, ^^^ '^"^^Pu per square kilometer, and the ^^^Pu/^^^'^''°Pu 

 ratios in each ten-degree latitude band are shown in Figs. 13 to 15, respectively. 



The distribution pattern for weapons plutonium shows heaviest deposition in the 

 northern hemisphere temperate latitudes and a minimum in the equatorial region. The 

 rise in the southern hemisphere temperate zone is, at its peak, about one-fifth of that in 

 the northern hemisphere maximum. The SNAP-9A ^^*Pu has an entirely different 

 distribution pattern. Most of the SNAP debris was deposited in the southern hemisphere 

 where the total fallout is 2.5 times as great as that in the northern hemisphere. 



Short-Lived Transuranic Radionuclides in Fallout from Nuclear Weapons Testing 



Nuclear debris from the past several Chinese tests has been examined to estimate the 

 radiation exposure resulting from individual short-Hved radioisotopes (Thomas, 1979a, 

 1979b, 1979c; Thomas and Jenkins, 1974; Thomas, Jenkins, and Perkins, 1976; Thomas 

 etal., 1976a, 1976b). Table 10 shows the ratios of the concentrations of '^^^Np and 

 ^^''U relative to ''^^Ba. It is evident that the ratios of each of these transuranium 

 elements to the major fission product, ''*°Ba, are rather high. This fact becomes 

 important when one calculates the radiation exposure from a submersion dose or from 

 ground shine. In fallout debris from such a test, the radiation exposure from these 

 short-lived transuranic radionuclides makes up a significant portion of the total exposure 

 of fresh fallout debris. 



