(B) Results for the Rhodium-102 High Altitude Tracer Experiment M. I, Kalkstein Air Force Cambridge Research Laboratories Introduction About 3 megacuries of pho? were produced as a tracer in the Orange Shot of the Hardtack series on 11 August 1958 at 2330 hours. This shot was an air burst at about 43 km above Johnston Island at about 16°N latitude and 170°W longitude. : The bulk of the debris is estimated to have almost certainly risen to above 100 km and probably went at least as high as 150 km, Rh}? decays mainly by electron capture, Measurement of its concentration was made by x-ray counting of the rhodium fraction which had been chemically separated from the original fiter samples. In addition to the 210-day half-life isomer, a longer-lived isomer of roughly four years half-life and the long-lived rni?? isomer were also produced, 2 The x-ray counts were corrected for the presence of these other activities by use of an empirical decay curve obtained for several stratospheric samples. Most of the results discussed are for stratospheric air filter samples collected by high-altitude aircraft. Results Results for samples collected above 19.4 km are shown in Figures 1 through 5. concentration as a function of time for different northern latitude regions. latitudes. Figure 1 presents the Figure 2 does the same for southern Figure 3 presents the concentration as a function of latitude during the first half of 1959, Figure 4 contains later data, and Figure 5 presents a latitude profile for samples collected during a single brief period. Discussion of Results As can be seen from Figure 1, there was a sharp increase in rn??? concentrations beginning in the late fall of 1959 and continuing through the early winter. This coincides well with the time one would expect down- ward mixing associated with the development of disturbances in the polar vortex region, These disturbances begin in about November and continue throughout the winter, being strongest about January. 3 The results are consistent with a picture of great downward mixing at high latitudes (centered about 60°) in the winter followed by horizontal movement in the low stratosphere. Figure 2 shows an increase in concentration during the Southern Hemisphere winter, again suggesting high latitude winter downward mixing as the mechanism. The Southern Hemisphere results also suggest that a relatively small fraction of the tracer appeared the first winter with a much larger fraction appearing in the second winter. From Figure 3, it is apparent that mixing across the equatorial region is slow at least on the time scale and the altitude region (about 20 km) represented by these values. Comparison of the early concentrations with later values indicates that the early rhodium in the low stratosphere is equal to only a few percent of the Orange 69