Natural environmental radioactivity and radon gas

In recent decades, much has been learned about the nature and sources of human exposure to naturally-occurring radiation and radionuclides. A brief historical perspective is given on this growth of knowledge, and recent assessments of the contributions of the various sources to human population radiation exposure are discussed. This provides the context for a consideration of the significance of exposure to airborne radon decay products for the global population and of future exposure of an increasing number of space travelers to cosmic radiation. (author). 13 refs, 4 tabs