Recoil refinements: Implications for the 40 Ar/ 39 Ar dating technique

Details Recoil refinements: Implications for the 40 Ar/ 39 Ar dating technique Recoil refinements: Implications for the 40 Ar/ 39 Ar dating technique

May 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995gecoa..59.1821o&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 59, Issue 9, pp.1821-1834

Computer Science

14

Scientific paper

Integration of the neutron energy distribution for a water-moderated reactor with the most recent cross-section data yields mean recoil energies of 177 keV for 39 K ( n, p ) 39 Ar, 969 keV for 40 Ca ( n , ) 37 Ar, and 140 eV for 37 Cl ( n , ) 38 Cl ( ) 38 Ar. These estimates are insensitive to the anisotropy of reaction products. Utilizing Monte Carlo simulations of collision cascades, we calculate a mean recoil range of 1620 å for 39 K ( n, p ) 39 Ar, 3780 å for 40 Ca ( n , ) 37 Ar, and 11 å for 37 Cl ( n , ) 38 Cl ( ) 38 Ar. Rutherford backscatter (RBS) measurements of argon implantation experiments into albite confirm the veracity of these estimates. Integration of the recoil range distributions yields a mean depletion depth in a semi-infinite medium of 820 å for 39 Ar, 1950 å for 37 Ar, and 6 å for 38 Ar. The concentration gradients generated by recoil-redistribution between thin slabs were then incorporated into standard diffusion equations. If the exsolution lamellae are the effective diffusion dimension for argon, then the calculations indicate that the argon release rates and age spectrum derived from incremental heating of minerals exsolved at the micron to submicron scale are significantly affected by recoil-redistribution. The age spectra will be discordant even if the feldspar has not experienced a complex or slow cooling history. Incremental step apparent ages will increase with the fraction of 39 Ar released as the potassium poor lamellae degas. The age spectra will exhibit decreasing apparent ages with increasing fraction 39 Ar released as the potassium feldspar lamellae degas. The overall profile of the age spectrum will depend upon the composition of the feldspar and the size distribution of the lamellae, if the lamellae are the effective argon diffusion dimension. In principal, these calculations can be used to discriminate between different models for argon diffusion in minerals. Finally, the 11 å mean recoil distance calculated for 38 Ar indicates that it is not a proxy for anion-sited excess argon. Instead, published correlations of 38 Ar with excess 40 Ar probably reflect the degassing of fine-grained, Cl-rich inclusions.

Affiliated with

Also associated with

No associations

Rating

Recoil refinements: Implications for the 40 Ar/ 39 Ar dating technique does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Recoil refinements: Implications for the 40 Ar/ 39 Ar dating technique, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Recoil refinements: Implications for the 40 Ar/ 39 Ar dating technique will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1060359