Mechanisms and kinetics of apatite fission-track annealing

Journal Article · · American Mineralogist; (United States)

OSTI ID:5667654

Carlson, W D ^[1]

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1. Univ. of Texas at Austin (USA)

Kinetic equations derived from a physical model of the atomic-scale processes involved in apatite fission-track annealing account for the dependence of annealing rates on temperature and time over the full range of these variables investigated experimentally to date. The physical model postulates radial shrinkage of the disrupted zone surrounding the path of the fission fragments, in response to the elimination of crystalline defects by short-range atomic repositioning during thermal annealing. For the case of a disrupted zone that is cylindrical near its axial center with regions of conical taper at each end, the model predicts a two-stage annealing process in which track-length reduction is dominated initially by axial shortening, and subsequently by segmentation of tracks. The model reproduces laboratory annealing data with an accuracy nearly equal to the uncertainty of the experimental measurements. Although the dependence of annealing rates on apatite composition cannot be accurately deduced from the experimental data presently available, an analogy to rates of O diffusion in silicates suggests that the kinetic parameters of the model may vary with composition as linear functions of the total ionic porosity. Experimental indications of annealing anisotropy can be explained under this model by invoking small differences in the geometry of the disrupted zone for different crystallographic orientations. Because this kinetic model is based on explicit physical mechanisms, extrapolations of annealing rates to the lower temperatures and longer time scales required for the interpretation of natural fission-track length distributions can be made with greater confidence than is the case for purely empirical relationships fitted to the experimental annealing data.

• OSTI ID: 5667654
• Journal Information: American Mineralogist; (United States), Journal Name: American Mineralogist; (United States) Vol. 75:9-10; ISSN AMMIA; ISSN 0003-004X
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ACTIVATION ENERGY
ANISOTROPY
ANNEALING
APATITES
CHEMICAL COMPOSITION
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DIFFUSION
ELEMENTS
ENERGY
EQUATIONS
FISSION FRAGMENTS
FISSION TRACKS
HEAT TREATMENTS
KINETIC EQUATIONS
MINERALS
NONMETALS
NUCLEAR FRAGMENTS
OXYGEN
PARTICLE TRACKS
PHOSPHATE MINERALS
POROSITY
SHRINKAGE
SILICATE MINERALS
TEMPERATURE DEPENDENCE
TIME DEPENDENCE