This chapter is concerned with radiation doses to the public from nuclear weapons tests, as well as those resulting from nuclear reactor accidents that have occurred over the years. Since the doses involved are mostly small (smaller than the doses from natural radiation), it is extremely difficult to pinpoint the health effects from these extra doses. This is a widely debated issue and will be discussed in more detail in Chapters 11 and 12. Here we will concentrate on the doses. During the period from 1945 to 1981, 461 nuclear bomb tests were performed in the atmosphere. The total energy in these tests has been calculated to be the equivalent of about 550 megatons of TNT (TNT is the abbreviation for trinitrotoluene). The bombs in Hiroshima and Nagasaki had a blasting power of, respectively, 15 and 22 thousand tons of TNT. Nuclear tests were particularly frequent in the two periods from 1954 to 1958 and 1961 to1962. Several nuclear tests were performed in the lower atmosphere. When a blast takes place in the atmosphere near the ground, large amounts of activation products are formed from surface materials drawn up into the blast. The fallout is particularly significant in the neighborhood of the test site. One of the best known tests with significant fallout took place at the Bikini atoll in the Pacific in 1954 (see next page).