A natural quartz sample was irradiated using a 200MeV proton beam in order to produce spallogenic 3He and 4He. Their temperature-dependent diffusivities were then determined simultaneously by means of high-precision stepped heating and noble-gas mass spectrometry. The outward mobility of the proton-induced species reflected diffusion through the quartz lattice. At 70 to 400C, the diffusion parameters were 84.5kJ/mol and ln(Do/a2) = 11.1ln[/s], for proton-induced 3He. The diffusion parameters for proton-induced 4He were indistinguishable from those for 3He; thus providing no evidence for the commonly expected inverse square-root of mass diffusion-relationship between isotopes.

Diffusion Kinetics of Proton-Induced 21Ne, 3He and 4He in Quartz. D.L.Shuster, K.A.Farley: Geochimica et Cosmochimica Acta, 2005, 69[9], 2349-59