Preprints
https://doi.org/10.5194/gchron-2023-13
https://doi.org/10.5194/gchron-2023-13
16 Jun 2023
 | 16 Jun 2023
Status: this discussion paper is a preprint. It has been under review for the journal Geochronology (GChron). The manuscript was not accepted for further review after discussion.

On etching, selection and measurement of confined fission tracks in apatite

Raymond Charles Jonckheere

Abstract. This work investigates the selection of horizontal confined tracks for fission-track modelling. It is carried out on prism sections of Durango apatite containing induced tracks with mean lengths of ~16, ~14, ~12, and ~10 μm. Suitable tracks are identified during systematic scans in transmitted light. The explicit selection criteria are that the tracks are horizontal and measurable. We measure the length, width, orientation, and cone angle of each selected track and in some cases other dimensions.

The confined track selection is in the first place dependent on a threshold width and in the second place on the requirement that the tracks are etched to their ends. In most cases the first condition implies the second, which decreases in importance as the tracks are shortened following annealing. The widest confined tracks, which must also be the shallowest, come to intersect the surface and are excluded. In general, the selection is dominated by the width of the etched tracks. This, in turn, depends on their orientation relative to the c-axis and the apatite etch rates, and their effective etch times. Despite the different geometrical configuration of the unetched host tracks and confined tracks, neither the angular distribution nor the etch time distribution of the confined track sample depends on the degree of annealing. This illustrates the general principle that those entities are selected that have the right properties for being selected. In this case etching-related factors determining the track width are the most important, while the known geometrical biases are second order. The track etch rate exhibits no demonstrable variation along the track, but signifi-cant differences from track to track. Moreover, although the track etch rate of induced tracks is not correlated with the extent of partial annealing, it is on average twice as high as the value for fossil tracks.

Our length measurements are in good agreement with the annealing models for this apatite and etch protocol. We submit that this is not fortuitous and that it is possible to select a representative confined track sample, and perform reproducible and meaningful confined track length measurements. Deliberate or inadvertent biasing, carelessness or inexperience will of course give different results, but these should be treated as statistical outliers, not as an indication that track lengths are fluid.

Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.
Raymond Charles Jonckheere

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on gchron-2023-13', Richard A. Ketcham, 13 Jul 2023
  • AC1: 'Comment on gchron-2023-13', Raymond Jonkheere, 26 Jul 2023
    • CC2: 'Reply on AC1', Richard A. Ketcham, 09 Aug 2023
  • RC1: 'Comment on gchron-2023-13', Anonymous Referee #1, 01 Aug 2023
    • AC2: 'Reply on RC1', Raymond Jonkheere, 03 Aug 2023
  • RC2: 'Comment on gchron-2023-13', Raymond Donelick, 01 Aug 2023
    • AC3: 'Reply on RC2', Raymond Jonkheere, 03 Aug 2023
  • AC4: 'Comment on gchron-2023-13', Raymond Jonkheere, 12 Aug 2023

Status: closed

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • CC1: 'Comment on gchron-2023-13', Richard A. Ketcham, 13 Jul 2023
  • AC1: 'Comment on gchron-2023-13', Raymond Jonkheere, 26 Jul 2023
    • CC2: 'Reply on AC1', Richard A. Ketcham, 09 Aug 2023
  • RC1: 'Comment on gchron-2023-13', Anonymous Referee #1, 01 Aug 2023
    • AC2: 'Reply on RC1', Raymond Jonkheere, 03 Aug 2023
  • RC2: 'Comment on gchron-2023-13', Raymond Donelick, 01 Aug 2023
    • AC3: 'Reply on RC2', Raymond Jonkheere, 03 Aug 2023
  • AC4: 'Comment on gchron-2023-13', Raymond Jonkheere, 12 Aug 2023
Raymond Charles Jonckheere
Raymond Charles Jonckheere

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Short summary
We investigate the relationship between damage trails from uranium fission in apatite and the etched tracks measured with an optical microscope. We aim to understand sampling biases and to improve etching, selection and measurement protocols. The track orientation and length, apatite and track etch rate, and effective etch time co-determine whether a track is suitable for measurement. Reliable data are attainable because the specific sample properties have but a limited effect on these factors.