The natural radiation environment and human modifications to that environment

For most populations of organisms, including humans, natural background is the main source of exposure to ionising radiations. In this chapter, the various sources of natural background are described, including cosmic rays and primordial radionuclides plus their shorter-lived progeny, and ranges of dose rates in various contexts are estimated. Human modifications to the natural radiation environment are then addressed. These include the fallout from nuclear weapons’ testing, mainly in the 1950s and 1960s. Also addressed are the enhanced exposure rates that arise during aircraft and spacecraft flights, and the potential significance of solar storms that can greatly increase the doses received.