C-14 excess with the tritium values (Figure 5). If the observations at 50, 000 feet are extrapolated to a zero C-14 excess, 7 x 10° atoms of tritium per gram of air are present. mates of expected concentrations (10° to2x 10! atoms/gm of air), This value formed the basis of the estiAn alternate minimum concentration estimate can be made assuming the 1.6 x 104 T.U. found in pre-bomb surface hydrogen gas is in equilibrium with the water vapor in the stratosphere. Such concentrations would be an order of magnitude smaller. The remarks concerning the utility of C-14 measurements also apply to tritium, although in the latter case uncertainties in background values are muchlarger. Rhodium-102. August 1958. An important tracer experiment was conducted in connection with the Orange shot in Three megacuries of Rh-102 were injected by a megaton device detonated at over 100, 000 feet. The resulting cloud rose to much higher altitudes. About 0.3 megacuries were produced in other experiments, so that over 90 percent of the Rh-102 in the atmosphere is of very high altitude origin. Figure 6 shows the distribution of this tracer in May 1960. distribution in the lower stratosphere. These data clearly show the non-uniform At about 65,000 feet the polar and temperate zones of both hemispheres show about an order of magnitude higher concentration than the equatorial region. Although the injection oc- curred at 17°N, the debris seems to be partitioned equally in the lower stratosphere in both hemispheres. It should be pointed out that a difficulty, which is now being resolved, exists in interpreting the Rh-102 data. There is a long-lived isomer, as well as the 210-day isomer, so that Rh-102 follows a complex decay scheme. half-life. All data reported here has been corrected from counting day to August 12, 1958, assuming a 210-day (This value has likewise been used to estimate current concentrations.) Therefore, although absolute values may be in error, the relative concentrations shown in Figure 6 are valid. This has been a unique experiment and still holds great promise of providing a useful high-altitude tracer. A maximum effort in the next few years should be directed to collecting and interpreting the rhodium data. Other Cosmic-Ray Isotopes, Several shorter-lived radioisotopes are produced by cosmic ray interactions in the atmosphere and may be useful in studying stratospheric models. are included in Table 1. Data for Na-22, 5-35, Be-7 and P-32 The first, Na-22 may still be present from artificial sources, The other isotopes are so short-lived that only naturally produced quantities are now present in the atmosphere. The most fruitful way of utilizing data on these isotopes is by determining the expected equilibrium concentration of the isotope in a quiescent atmosphere and examining the deviations from equilibrium in the actual atmosphere. The production by cosmic rays is a function of geomagnetic latitude and altitude. Several investi- gators have computed the equilibrium concentrations to be expected in the absence of transport or diffusion. As an example of this type of analysis, Figure 7 shows a comparison of the observed Be-7 data with the computed equilibrium concentrations. (The latter are shown symmetrically about geographic latitude as an ap- proximation to geomagnetic latitude.) As can be seen, the tropospheric concentrations are well below the equilibrium values, showing evidence of the rapid tropospheric removal process. Stratospheric concentrations are much closer to equilibrium values, with the ratio of observed to equilibrium values approaching one at the highest altitudes. The stratospheric departures from equilibrium can be the result, among other things, of mixing with the troposphere or of a poleward circulation bringing in Be-7 poor air from the tropics. 32