Worldwide Fallout 



R. W. PERKINS and C. W. THOMAS 



Since the first nuclear weapons test at Alamogordo, N. Mex., on July 16, 1945, 

 approximately 360,000 G (360 kCi) of '^^-^'^'^Pu lias been injected into the atmo- 

 sphere. In addition, 1 7,000 G (17 kG) of^^^Pu entered the atmosphere in April 1964 as 

 a result of the high-altitude burnup of a SNAP-9 satellite power source. Since most of the 

 plutonium from nuclear weapons testing, as well as tliat from the SNAP-9 burnup, 

 entered the stratosphere, fallout lias been worldwide. The deposition is influenced by 

 meteorological conditions and also by topographical features of the earth s surface. 

 Residence time in the stratosphere is about 10 to 11 months: however, because of the 

 high-altitude burnup of the SNAP-9 device, it was 2 yr before significant amounts of this 

 debris reached the earth s surface. 



In addition to plutonium, substantial amounts of '^^^ Am are formed from the decay 

 of the weak beta emitter ^"^^ Pu and are an important constituent of fallout. 



Tlie majority of radioactivity entering the stratosphere during this past decade has 

 been a result of the Giinese nuclear weapons testing. Tlie ratio of plutonium to ^^'^ Cs has 

 been relatively constant throughout the nuclear weapons period, and thus a measurement 

 of ^^"^Cs permits a reasonable estimate of the plutonium deposition. The ratio of 

 transuranic elements in fallout is substantially different from tliat in power reactor 

 wastes, which contain far more americium and curium relative to plutonium. Fresh 

 fallout from thermal nuclear weapons contains large amounts of short-lived ^^'^U and 

 ^^^Np, and these may contribute substantially to the radiation exposure at the earth's 

 surface. 



The first significant injection of transuranium elements into the atmosphere occurred as 

 the result of the nuclear weapons testing in Alamogordo, N.Mex., on July 16, 1945. 

 Between then and 1952 further nuclear detonations resulted in additional injections to 

 the atmosphere; however, because of their relatively low yield, most of this debris was 

 confined to the troposphere. On Nov. 1, 1952, the first thermonuclear device was 

 detonated. This 14-Mt explosion injected large amounts of debris into the stratosphere. 

 The relatively high energy yield of this fusion device, together with a much higher 

 integrated neutron flux, greatly increased the production of the transuranium elements. 

 The majority of the transuranium elements and other nuclear debris which has been 

 injected into the atmosphere was produced during the 1961 and 1962 United States 

 (U. S.) and Union of Soviet Socialist Republics (U.S.S.R.) nuclear testing programs. A 

 nuclear weapons test-ban agreement between the United States, United Kingdom, and 

 Soviet Union in early 1963 suspended atmospheric testing. However, in late 1964 the 

 Chinese exploded their first atmospheric nuclear test, and since that time they have 

 continued testing in the northern hemisphere. France was not a member of the test-ban 

 agreement, and in mid-1966 they began atmospheric testing in the southern hemisphere. 

 The test-ban agreement in 1963 did not rule out underground. tests, which do not vent to 



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