Table 5—- RADIONUCLIDE RATIO DATA FOR 1962 IMPACTOR- FILTER COLLECTIONS Samplingaltitude interval Fraction ‘44Cce/%sr MIR,sr 140B a/M4Ce Mar. 16, 1962 9.1~14.4 Stage 1 Stage 2 Filter 6.74 + 3.32 25.7 + 1.4 25.3 + 4.8 <0.2 0.100 + 0.023 <1.7 < 0.03 0.00389 + 0.00088 < 0.07 14,4=— 21.3 Stage 1 Stage 2 Filter 1.40 + 0.65 37.3 + 4.2 40.4+1.8 < 0.3 0.650 + 0.083 <0.78 <0.2 0.017 + 0.001 <0.019 © 21.3~— 27.4 Stage 1 3.1 + 1.0 0.30 + 0.19 <1] 0.021 + 0.011 <0.5 27.4~— 29.8 Stage 1 > 0.6 Filter 4.2421 Stage 2 Filter Stage 2 14.1 + 4.5 1.87 + 0.36 . >8 Sept. 25, 1962 9.1—-15.2 Stage 1 54 + 34 Filter 19 +9 Stage 2 28.0 + 3.0 45,.2— 21.3 Stage 1 > 40 21.3—27.4 Stage 1 Stage 2 > 20 6.24 + 2.35 Stage 1 4.2 + 3.4 Filter > 5.2 Stage 2 Filter Filter 27.4— 29.6 Stage 2 31.0 + 7.7 39.4 + 6.9 12+7 >9 If one of the primary causes of chemical fractionation is the presence of gaseous precursors in fission-product decay chains, one might have expected fractionation between ‘4Ce and Sr. The mass-144 chain has no known gaseous precursors except for the extremely short-lived xenon, whereas the mass-90 chain includes 1.4-sec-bromine and 33sec-krypton precursors. It appears, therefore, that the particle size distribution of “‘Ce and “Sr in debris of this age is independent of considerations of the gaseous nature of precursors. ACTIVITY RATIOS For the comparison of the size distributions of individual radionuclides within each given flight and over all flights, it is best to con- Sider activity ratios. Direct insight concerning the possibility of chemical fractionation between specific radionuclides can be obtained. Tables 5 and 6 contain all activity-ratio data, corrected for radioactive decay to the flight date, obtained for the 1962 and 1963 impactor —filter