AMERICIUM a Bx n “7 Many of the samples collected in the 1959-1970 background survey were also analyzed for their 241am content. Aircraft sampling was normally conducted in the vicinity of three latitudes: 70°N, 35°N, and 10°N. Stratospheric samples were collected quarterly at altitudes ranging from 40,000 to over 60,000 feet. For brevity, the details of the individual sample collection are omitted in this manuscript. The measurements were performed at McClellan Central Laboratory and Tracer Lab West--now called L.F.E. Environmental Laboratories. NN = ° “e 7 2 As an om = a z aon ain omwy a wm SBA RAMA A at seen OOmtnAaAa so py F 8 Ce * rr id nw "8s 7 It ig interesting to note that the 24tam/239pu atom ratio in the atmosphere increased yearly from 1963-1967. This was the result of intermixing of debris © ©» © © © © #8 8 8 er oorocomoe 7 wa ~~ Ono om ~ 2 we e FF en to 733py were superimposed over the previous inventory. The net effect is an increase in the total atmospheric 235pu relative to 24tam, CONCLUSIONS The 240py/2 35py isotope ratios in the atmosphere have changed with time. A possible explanation for this variation is that recent injections of debris Play a major role in determining the characteristics of the transuranic elements in the atmosphere. Measurements of stratospheric 2"!Am from 1963-1970 seem to indicate that as a first approximation, the 24lam burden of the atmosphere may be considered as a The 2"1Am concentration of the atmosphere decreased from a high of 5.92 x 10° atoms/SCM in 1963 to 0.27 x 10° atoms/SCM Table 3. during 1967 and subsequent years containing smaller quantities of 744m relative 241 ay Background Summary 1963-1970 To a lesser extent, the 241am/233pu ratio was influenced by the ingrowth of 2%!am from the decay of 24lpy, From 1967-1970, the americium/plutonium ratio decreased in contradiction with expectations. The reason for this anomaly is that much of the old debris that was injected from 1956-1963, containing relatively large quantities of “lam, has been removed from the atmosphere. The fresh injections of debris 260 —T Ls When sets of 74!Am data are averaged, general trends become apparent. ‘Table 4 shows the average annual @"?am and 24!4m/23%Pu levels obtained by averaging the data reported in Table 3 on a yearly basis. The data seem to indicate that as a first approximation, one may assume that all the atmospheric americium was injected as a point source in 1963. This burden decreased with an apparent half-life of 1.6 years. point source injection during 1963. 8 & 8 2 es ars $ It is interesting to note that the concentration of 74 JAm 8 8 &© aA Mat Mm aAe aw 2 ‘B| as well as the ?"lam/23%pu ratios vary from sample to sample. The amount of 241am formed is a function of both the age and irradiation history of the debris. containing different relative amounts of 74am. Sade 8 »_ F o Table 3 shows the results of the study for samples whose measurement uncertainty were less than 25%, Qo nn oe warm mem ot = * a Ay m7 an % ~ ped ~Tinnw eo aera som ~on my wn MMT ATOM OODWOHTeNegaannas as o ~ 5 wy 2) $s ' oOann 4a Att onom ae CASK GS mnwoonrnor NMwtownrne DOnon DO AN AN ON NOON ANAM MINN aT ol o_ a a a bn o A f RRR MHRMXESE TIMM OW Ow Oo a * a]= fa “ <| nan Wt MM a Mt Mohd Be SSS5SS6SSS55555995555S33 o Fatt tT THAN 3a at