62 



TRANSURANIC ELEMENTS IN THE ENVIRONMENT 



TABLES (Continued) 



*Date of announcement not necessarily shot date. 



|Mr. McCone on Oct. 24, 1958, announced that these seven tests had a high yield, meaning that 

 each had an explosive power equal to millions of tons of TNT. 



their decay properties and half-lives. Their total activities are normalized to ^^^Pu to 

 permit comparison of their relative production rates. The radioisotope ^"^^Pu (a 

 beta-decay isotope with a 14.7-yr half-life), which decays to ^"^^Am, is the most 

 abundant activity. 



The distribution on the earth's surface of transuranic elements produced during 

 nuclear weapons testing depends on whether the debris is contained in the stratosphere or 

 troposphere. Such partitioning is dependent on many things, including yield of the 

 device, the "burst" height, and the height of the troposphere. Figure 1 shows the percent 

 of debris in the troposphere as a function of the yield of a nuclear device (Ferber, 1964). 

 From these data it can readily be seen that devices in the low-kiloton range place most of 

 the debris in the troposphere, whereas weapons in the megaton range inject most of the 

 debris into the stratosphere. Prior to 1952 all the nuclear explosions were in the 

 low-kiloton range; the residence time for this debris is about 20 to 40 days (Stewart, 

 Crooks, and Fisher, 1955; United Nations, 1964; Krey and Krajewski, 1970a). 

 After 1952 numerous multimegaton tests took place in which most of the debris was 

 injected into the lower stratosphere where the residence half-time is about 1 yr (Thomas 

 etal., 1970). 



