70 TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



reasonably constant in fallout since the U.S. and U.S.S.R. nuclear tests of 1961 and 

 1962. These data are based on measurements beginning in 1962 at Richland, Wash. 

 (46°N), and in later periods in New York, N. Y. (4rN), and Harwell, England (52°N). 

 The ^^^'^'*^Pu/^ ^^Cs ratio appears to be constant in most cases within the accuracy of 

 the measurements and thus tends to indicate a general constancy of the transuranium 

 production and atmospheric behavior relative to that of the fission products. 



100 



E 10 



CO 



O 



c 



■D 



>10 Mt 



1 to 10 Mt 



0.1 to 1 Mt 



0.02 to 0.1 Mt 



Harwel 



Richland, Wash., Measurements - 



1 — 



I I I 



YEAR 



Fig. 5 Concentrations of '^^Cs in surface air at 46°N latitude since 1953. The 

 concentrations prior to 1962 were estimated by normalizing concentrations measured at 

 Harwell, En^and. 



On the basis of observed '^^Cs concentrations at 46°N latitude since 1962 and an 

 extrapolation back to 1953 by normalizing Harwell, England, to Richland, Wash., ' ^^Cs 

 air concentrations during the period 1962 to 1964 (as indicated in Fig. 5), it should be 

 possible to obtain a good estimate of the airborne plutonium concentrations during this 

 entire period. Such extrapolations are, of course, subject to some uncertainty. 



An atmospheric sampling program using high altitude aircraft has been conducted 

 since 1959 (Hardy, 1973). Sampling aircraft normally operate at four latitudes — 70°N, 

 35°N, 10°N, and 40°S. Sampling altitudes normally range from 15.000 to 70,00011. 

 Figure 6 shows the ratios of ^"^^Pu to^-^'^Pu, ^'"Pu to ^^'^Pu,and ^''^Pu to "^Pumair 

 at 70°N latitude as a function of time. It is evident that there is considerable variation in 

 these ratios which is undoubtedly associated with the type and energy of the weapon 

 responsible for the plutonium isotope production. There is a substantial increase in the 

 heavy-to4ight plutonium isotopes immediately following the 1961 and 1962 U.S.- 

 U.S.S.R. test series. 



Figure 7 shows the concentrations of ^^^Pu and 239,240p|j j^om 1962 to the 

 present. These measurements, which were made near Richland, Wash., show that seasonal 

 variations in the ^^^ ,2 3 9,2 4 0pu ^^^.^ gjp^jigp ^q those of other nuclear-weapons-produced 

 radionuclides of stratospheric origin; maximum concentrations occur in the late spring. 



