1. Introduction
2. Summary of Atmospheric Nuclear Explosions (¹³⁷Cs)
3. Cumulative Fallout Record (¹³⁷Cs)
4. Cesium Baseline (to 1986)
5. Plutonium and Americium Baseline
6. Radioiodine, Strontium and other nuclides
7. Naturally Occurring Radionuclides (NOR)

Weapons testing radioactive contamination was spread world-wide not only in tropospheric fallout (often associated with rainfall events but with extensive, close-in, dry deposition) but also in stratospheric fallout. The patterns of stratospheric fallout which provide a baseline of contamination against which to compare the impact of the Chernobyl accident resulted in a fairly even distribution of contamination over most of the earth's surface. Peak concentrations of stratospheric fallout were achieved between 1962 and 1964. The 1963 joint U.S.-Russian-British test ban treaty effectively ended atmospheric weapons testing, at which time fallout rates began declining, with occasional interruptions from Chinese weapons tests, until the Chernobyl accident in 1986. Prior to the Chernobyl accident, world-wide fallout levels had reached the lowest level of yearly accumulation since 1950. Other important source points of anthropogenic radioactive contamination include fuel reprocessing facilities such as Sellafield, the Savannah River Reservation, accidents such as the SNAP satellite failure in 1958, and the many other U.S. and Russian military weapons production sites, such as the Hanford Reservation in Washington. These sites are not only sources of significant releases in the past but they also pose a risk of substantial releases to the environment for centuries to come. See RAD 11, for a summary of these source points of anthropogenic radioactivity.
 

2. Summary of Atmospheric Nuclear Explosions (137Cs)

The following table gives a quantitative description of the number and yield of nuclear explosions occurring before the Chernobyl accident. The baseline data which follow the list of weapons test explosions document the impact of these tests prior to the Chernobyl accident in 1986. The Chernobyl disaster marks the beginning of a second era in the anthropogenic contamination of the biosphere with nuclear effluents (See RAD 10); hopefully, Chernobyl was an isolated incident rather than the first in a series of serious nuclear accidents.
 

(1)Aarkrog, A. (1991). Source terms and inventories of anthropogenic radionuclides. Roskilde Denmark: Riso National Laboratory.