TABLE 1 RADIOISOTOPES ABOVE 100, 000 FEET Minimum Isotope Half-life countable Expected concentration (1961) dpm C-14 5670 years 0.5 Maximum dpm /1000 SCF 500 (10 x background) Minimum dpm/1000 SCF 50 (background) OCF needed for: Maximum Concen- Minimum Concen- tration tration 1 10 Remarks CO, gas or-90 28 years i 500 10 2 100 Particulate Cs-137 27 years 1 1000 20 1 50 Particulate Pb-210 22 years 1 1 10° Particulate H-3 12 years 0.5 12 years 0.5 (as Ho) H-3 (as Hy) 8 (105 T.U.) 6 x 104 0.01 103 0.08 60 (103 T.U.) 300 (2x 10° atoms/gm) (10° atoms/gm 6000 0,007 5 30 Na-22 2.6 years Rh-102 1 210 days 1 S-35 87 days Be-7 P-32 107} - Gas (1.6 x 104 T.U.) i074 104 1SCF = 6x105 to 3.x 1073 gm 15 Water Vapor 107 Particulate 1000 1 1 1000 Particulate 1 200 20 5 50 Particulate 53 days 10 2000 200 5 50 Particulate 14 days 1 20 2 50 500 Particulate To obtain ambient volumes at: 105, 000 feet, multiply SCF by 100 160, 000 feet, multiply SCF by 1,000 220,000 feet, multiply SCF by 10, 000 The latest balloon stratospheric C-14 data (1960) which is available only from San Angelo, Texas, shows a distribution similar to that at San Angelo in 1955, with some evidence that the peak concentration is below 90, 000 feet. However, there may be a peak due to Teak and Orange above 90, 000 feet. Because of the ambi- guity in possible sources, it will be necessary to follow the existing distribution of C-14 in space and time to study the role played by the atmosphere. It does have the advantage of being a gaseous tracer and can be pre- sumed to move with the air parcels. Strontium-90. A series of aircraft filtering flights were made in May and early June 1960 to collect radio- activity on a world-wide basis at four latitudes and at altitudes from 15, 000 to over 65, 000 feet. These data, supplemented by balloon collections made at San Angelo, Texas, to 90,000 feet and by preliminary results of surface air concentration measurements made by the Naval Research Laboratory, are shownin the figures. The data are expressed in d/m/1000 scf on sampling day, unless otherwise indicated. Values in italics refer to observations reported as tropospheric. The distribution of Sr-~90 is shown in Figure 2. As can be seen, the lowest stratospheric concentrations appear in equatorial regions, with somewhat higher values in the temperate and polar stratosphere. It is some- what surprising to see that the southern hemisphere stratospheric concentrations are the same or slightly higher than the northern hemisphere values, despite the fact that almost all of the Sr-30 was injected north of the 26