Quantifying the diffusion kinetics and spatial distributions of radiogenic 4He in minerals containing proton-induced 3He

Apatite, titanite and olivine samples were bombarded with a similar to150 MeV proton beam to produce similar to10(8) atoms/mg of spallation He-3. High-precision stepped-heating experiments were then performed in which the artificial He-3 and, for apatite and titanite, the natural radiogenic He-4 were measured to characterize the diffusive behavior of each isotope. Helium-3 diffusion coefficients are in excellent agreement with concurrently and/or previously determined He diffusion coefficients for each mineral. Our results indicate that proton-induced He-3 is uniformly distributed and that radiation damage associated with a proton fluence of similar to5x10(14) protons/cm(2) does not cause noticeable changes in He-4 diffusion behavior in at least apatite and titanite. Proton-induced He-3 can therefore be used to establish He diffusion coefficients in minerals with insufficient natural helium for analysis or those in which the natural He-4 distribution is inhomogeneous. In addition, step-heating He-4/He-3 analysis of a mineral with a uniform synthetic He-3 concentration provides a means by which a natural 4He distribution can be determined. (C) 2003 Elsevier B.V. All rights reserved.