Long-lived radionuclides as tracers in terrestrial and extraterrestrial matter

Radionuclides in nature offer unique opportunities for radioactive dating and tracing of natural and man-made processes. Naturally occurring radionuclides with half-lives between a few days and 10(12) a have found widespread applications some of which are surveyed here. After a short glance on radionuclide production in stellar nucleosynthesis and on extinct radionuclides in the early solar system, applications are discussed of the long-lived (5 ka < T-1/2 < 16 Ma) radionuclides Be-10, C-14, Al-26, Cl-36, Ca-41, Mn-53, Ni-59, and I-129 in cosmochemistry and -physics and in the earth and environmental sciences. These nuclides occur in nature as cosmogenic and partially as radiogenic nuclides and some of them were brought into the terrestrial environment by man. Methods to analyze them at their natural levels are reviewed. Applications are highlighted which cover the cosmic ray record in extraterrestrial matter and in various terrestrial compartments and archives. Emphasis is put on the distinction of mechanisms affecting constancy or variability of the observed natural radionuclide abundances. Finally, the longterm human impact on the radiation environment and the relevance of long-lived radionuclides for the human radiation exposure is discussed.