Summary of apatite fission-track (AFT) analysis carried out in the labs of the ESD Group, University of Tübingen

In the following, a short summary of the preparation for apatite fission-track analysis is given. All steps are described in more detail and with pictures in additional documents.

In general, we use the external detector method and determine ages via zeta-age calibration. On apatites, etch pit diameters (Dpar) are measured and, if possible, track length data are acquired.

• Mineral separation. Mineral separation is carried out using standard procedures of crushing, sieving, and density and magnetic separation.

• Embedding of apatites in epoxy resin. The apatites are mounted using Struers FlexiForm embedding forms. Mounts come out as cylinders of ~1.5 cm height.

• Grinding and polishing of apatite mounts. Apatite mounts are grinded and polished to expose internal, even crystal surfaces. Mounts are grinded manually and polished using a polishing machine.

• Cutting and grinding of mounts to fit irradiation tube. The mounts are grinded and cut to fit the tube used during irradiation. In the end, the mounts are ~1 mm thick and 20 mm in diameter.

• Etching of apatites. Apatites are etched in 5.5 Mol HNO₃ for 20 seconds at 21°C to reveal spontaneous fission tracks that intersect the apatite surfaces.

• Packing of apatite mounts with mica external detectors, apatite standard mounts with micas, and dosimeter glasses with micas. Mounts of samples and standard material (Durango and Fish Canyon Tuff), as well as dosimeter glasses (used to monitor the neutron flux during irradiation), are covered with uranium free muscovite external detectors (50 µm thick). All mounts are stacked between the two dosimeter glasses (IRMM-540; 15 ppm uranium).

• Irradiation. To irradiate the mounts with thermal neutrons, we use the research reactor facility FRM II of TU München, Garching, Germany.

• Unpacking of the irradiation stack and etching of micas. The irradiation stack is unpacked and the mica external detectors are etched in 40%-HF for 30 minutes at room temperature to reveal the induced tracks.

• Preparing of glass slides with apatite mount and mica for analysis. For analysis, mounts and mica are glued or taped side-by-side (as mirrors) to glass slides.

• Analysis. Spontaneous and induced fission tracks are counted at 1000x magnification using a Zeiss AxioImager M2m microscope equipped with an AutoScan stage and using the TrackWorks software. Etch pit diameters (Dpar) and, if possible, track length data are acquired. Fission-track ages are calculated via the zeta-age calibration, i.e., each user determines his/her own zeta calibration factor using standard material of known age.

Summary of zircon fission-track (ZFT) analysis carried out in the labs of the ESD Group, University of Tübingen

In the following, a short summary of the preparation for zircon fission-track analysis is given. All steps are described in more detail and with pictures in additional documents. In general, we use the external detector method and determine ages via zeta-age calibration.

• Mineral separation. Mineral separation is carried out using standard procedures of crushing, sieving, and density and magnetic separation.

• Zircon mounting. Zircons are embedded into thin Teflon slides as Teflon withstands the etching procedure for zircons. The corners of the rectangles are then cut to eventually fit into the tube used during irradiation.

• Polishing of zircon mounts. Zircons are polished to expose internal, even crystal surfaces using a polishing machine with different polishing suspension sizes.

• Etching of zircons. Zircons are etched in a KOH:NaOH eutectic melt at 228°C to reveal spontaneous fission tracks that intersect the zircon internal surfaces. The etching duration depends on the age and the uranium content of the zircons. After the etching, the ZFT mounts are flattened between two thick glass plates.

• Packing of zircon mounts with mica external detectors, zircon standard mounts with micas, and dosimeter glasses with micas. Mounts of samples and standard material (Durango and Fish Canyon Tuff), as well as dosimeter glasses (used to monitor the neutron flux during irradiation), are covered with uranium free muscovite external detectors (50 µm thick). All mounts are stacked between the two dosimeter glasses (IRMM-541; 50 ppm uranium). (Instructions for AFT packing apply, with the difference of the dosimeter glasses and a different shape of the mounts and micas).

• Irradiation. To irradiate the mounts with thermal neutrons, we use the research reactor facility FRM II of TU München, Garching, Germany.

• Unpacking of the irradiation stack and etching of micas. The irradiation stack is unpacked and the mica external detectors are etched in 40%-HF for 30 minutes at room temperature to reveal the induced tracks.

• Preparing of glass slides with zircon mount and mica for analysis. For analysis, mounts and micas are glued or taped side-by-side (as mirrors) to glass slides.

• Analysis. Spontaneous and induced fission tracks are counted at 1000x magnification using a Zeiss AxioImager M2m microscope equipped with an AutoScan stage and using the TrackWorks software. Fission-track ages are calculated via the zeta-age calibration, i.e., each user determines his/her own zeta calibration factor using standard material of known age.

 Excel spreadsheet to caculate the chemical composition of the samples for irradiation