208 PERKINS, THOMAS, AND NIELSEN nized, and recently reported measurements for this filters collected prior to the 1961 test series’ have centrations ranging from 1 dis/min per 10° cu ft below to 460 dis/min per 10° cu ft above the tropopause. Our purpose of air shown air conthe tropopause measurements show concentrations ranging from 4 to 40 dis/min per 10° cu ft in the troposphere to 12,000 dis/min per 10° cu ft in the stratosphere. This suggests that a large amount of 7*Na was injected into the atmosphere during the 1961 and 1962 series of tests. Cesium-134 appears to be produced in nuclear detonations mainly by an (n,y) reaction on 'Cs, but it is also produced directly by fission.° The ratio of ‘*Cs to "Cs during the past 2'/, years has not shown a pronounced drop; however, our biological studies’ have shown that the ratio of these radionuclides in Alaskan caribou flesh dropped by a factor of 4 during the period from just prior to the 1961 test series through July 1963. This suggests that a major injection of 134Cs into the atmosphere occurred prior to the last test series. The radionuclides *°Co and *Mn were reported to be present in the atmosphere in 1958 by Marquez et al.,° who found them in rainwater collected between June 1957 and March 1958, Their presence was attributed to thermonuclear testing. It was recently reported’ that a number of activation products including “Mn, °°Fe, and 24Sb were produced in relatively high abundance in the high-yield detonations carried out by the Union of Soviet Socialist Republics (U.S.S.R.) at Novaya Zemlya in the fall of 1961 and that ®y and '*Sb were produced in U.S.S.R. tests in late 1962. These tests appear to be the major source of the “Mn, “co, *y, and “Sb. The radionuclides *Y and ‘Sb were first observed in our studies during November 1962 and January 1963, respectively. Both “Mn and ®°Co showed a sharp rise during January and February 1963. This indicated an additional injection of these radionuclides. Beryllium-7 is produced by cosmic-ray spallation reactions in the atmosphere; its presence was first reported in the atmosphere by Arnold and Al-Salih® in 1955, who chemically separated it from rain- water samples. Measurements of its concentration in the atmosphere at various altitudes and latitudes have since been reported.*:!":!! Only recently have we begun to study the concentration of "Be in the atmosphere. It is interesting that, unlike other fallout radionuclides, "Be has not shown a large seasonal concentration change. Plutonium-239 was separated chemically from air filters after gamma-ray spectrometric analysis. Its concentration change with time is somewhat similar to that of 'Cs (see Fig. 6) but shows a larger increase during 1962. The ratios of *°Pu to "Cs as a function of time are given in Table 2; they show a relatively large peak with its maximum in October 1962. Alpha-particle-energy analysis of the plutonium separated