Radionuclides as tracers

The role of radionuclides as tracer of the chemical transport in river is also reinforced by the fact that each of the U-Th-Ra elements has several isotopes of very different half-lives belonging to the U-Th radioactive series. Thus, these series permit comparison of the behavior of isotopes of the same element which are supposed to have the same chemical properties, but very different lifetimes. These comparisons should be very helpful in constraining time scales of transport in rivers. This was illustrated by Porcelli et al. (2001) who compared ( " Th/ U) and ( °Th/ U) ratios in Kalix river waters and estimated a transit time for Th of 15 10 days in this watershed. The development of such studies in the future should lead to an important progress in understanding and quantifying of transport parameters in surface waters. This information could be crucial for a correct use of U-series radioactive disequilibria measured in river waters to establish weathering budgets at the scale of a watershed. 

Short Lived Cosmic Ray-Produced Radionuclides as Tracers of Atmospheric Processes... 

Baskaran, M. (1999) Particle-reactive radionuclides as tracers of biogeochemical processes in estuarine and coastal waters of the Gulf of Mexico. In Biogeochemistry of Gulf of Mexico Estuaries (Bianchi, T.S., Pennock, J.R., andTwilley, R.R., eds.), pp. 381-404, John Wiley, New York. 

Krishnaswami, S., Benninger, L.K., Aller, R.C., and Von Damm, K.L. (1980) Atmospherically-derived radionuclides as tracers of sediment mixing and accumulation in near-shore marine and lake sediments evidence from 7Be, 210Pb, and 239,240pu Earth planet Sci Lett 47> 307-318. 

At constant rj, the net counting rate / = / — /q is proportional to the activity A, and for many purposes, such as determination of half-lives or application of radionuclides as tracers, measurement of the relative activity, given by / at constant t], is sufficient. 

Fundamental to the use of natural radionuclides as tracers of particle transport is an understanding of the rates and mechanisms of radionuclide transfer from solution into the particulate phase. In a closed system, where no mechanism exists for the physical separation of a daughter nuclide from its parent, the decay series reach steady state... 

Recognizing that scavenging of dissolved radionuclide tracers is a reversible process was a milestone in understanding the removal of particle-reactive substances from the ocean. This principle must be taken into account in using natural radionuclides as tracers of particle transport, and when using natural radionuclides to infer the rates of processes responsible for scavenging particle-reactive substances (e.g., trace metals) from the ocean. 

Benninger, L. K. (1976). The uranium-series radionuclides as tracers of geochemical processes in Long Island Sound. Ph.D. Thesis, Yale University, New Haven, Connecticut. 

Production of radionuclides as tracers for research, industry, and medicine (see Vol. 4). 

Chemical yields are determined from tracer activities added to the analytical aliquots however, the yields can also be determined from short-lived activities that are present in the sample due to secular radioactive equilibrium. For example, the chemical yield of uranium can be determined from the recovery of an added tracer activity, but in plutonium samples it can also be determined from There is a 0.00245% branch for the decay of Pu by Qt-particle emission. If it is known that the plutonium sample was last purified more than a month ago, one can assume that 6.75-day in the analytical samples is in equilibrium with ""Pu, with a concentration defined by the branching ratio of activityf U)/activity( Pu) = 2.45 X 10 Similarly, radium is traced with 3.66-day " Ra, in secular equilibrium with the decay of 1.9-year Th. Use of intrinsic short-lived radionuclides as tracers requires that the time at which they were isolated from their parent activities is known precisely. 

Radionuclides as tracers provide tools of major importance in environmental research when used in conjunction with other ecological approaches, and provided careiiil laboratory and/or field-enclosure experiments designed to determine mechanisms accompany extensive field applications. 

Nelson, D. M., P. F. Gustafson and J. Sedlet. 1970. Fallout radionuclides as tracers of lake mixing. Proc. Conf. on Great Lakes Research 13(1) 490-494. 

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