Chapter 9 - Nuclear Weapons

Abstract

The testing of nuclear weapons in the atmosphere has been responsible for the largest quantities of man-made radionuclides released into the environment. The radioactive debris from nuclear explosions divides into three fractions, depending on the height of burst and explosive yield. The first of these fractions consists of the larger particles that fall out within a few hours and that are intensely radioactive. The second fraction is dispersed into the troposphere, but it may not produce fallout during the first day, because the particles are sufficiently small to behave somewhat like aerosols and are subject to the laws of dispersion and rainout that govern small particles. The third fraction penetrates the stratosphere and will deposit worldwide over a period of many months. The tropospheric fallout tends to be distributed in bands at the latitude of detonation, whereas the stratosphere debris distributes itself globally. The physical and chemical characteristics of the particles have been observed to be highly variable in several respects. Depending on the temperature-time history of the particle, the radioactivity can be coated on the surface or distributed throughout. The extent to which a given explosion produces radioactive fallout in its immediate vicinity depends on the size of the explosion and its height above ground. The first U.S. tests of nuclear weapons after World War II took place in the Marshall Islands in 1946. The Soviet Union conducted its first explosion in 1949, following which the United States accelerated its rate of testing and constructed second proving grounds near Las Vegas, Nevada. This chapter deals with the U.S. experience during the 193 test explosions in the open atmosphere and many more tests conducted underground. Information about the USSR experience is beginning to emerge as a result of the dissolution of the USSR and associated changes in public information policies.