Dept. of Earth and Env. Sci.

Masaya Volcano, Nicaragua 
Cosmogenic Isotope Laboratory

Udo Fehn, Professor of Geology

Post-Doctoral Researcher

Graduate Students

Former Students

Recent Publications

Undergraduates

U of R Earth and Environmental Sciences

Background:

Cosmogenic isotopes derive their name from the fact that they are formed as a consequence of the interaction of cosmic rays with atoms of the atmosphere, hydrosphere, or the top layers of the lithosphere. Although the group includes stable isotopes such as ³He, most of the isotopes in question are radioactive. Commonly we refer to ¹⁰Be, ¹⁴C, ²⁶Al, ³⁶Cl, ⁴¹Ca and ¹²⁹I as part of this group.  In spite of their commonly used name, most of these isotopes are also produced by processes other than interaction with cosmic rays; in particular, nuclear reactions in the crust and the anthropogenic nuclear activities have added significantly to the total concentrations of these isotopes. Because these isotopes have generally very low concentrations and relatively long half-lives with correspondingly low levels of radioactivity, they cannot (with the exception of ¹⁴C) be measured with methods such as conventional mass spectrometry or counting techniques.  The development of accelerator mass spectrometry (AMS) has made the detection of these isotopes at the low natural levels possible, and has opened up a wide field of applications, in areas such as hydrogeology, oceanography, geomorphology, and  volcanology.

 The release into the environment of some of these isotopes from nuclear explosions and reprocessing has also made possible applications of these isotopes in environmental studies and in short-term geologic questions.

At the Cosmogenic Isotope Laboratory, we have used mainly two of these isotopes, ¹²⁹I and  ³⁶Cl, which have half-lives of 15.7 Ma and 301 ka, respectively.  We have used these isotopes particularly in the tracing and dating of aquifers (Fehn et al.,1992; Rao et al., 1996), of fluids associated with hydrocarbons (Fehn et al., 1990; Moran et al.,1995) and of organic material in marine sediments (Moran et al., 1998). Samples are prepared at our laboratory and sent for analysis to the PRIME Laboratory at Purdue University.

Iodine-129 is derived  from cosmogenic, natural fissiogenic, and anthropogenic sources.