When swift heavy ions (SHIs) penetrate a solid, they leave narrow straight trails of permanent damage along their trajectory, the so-called ion tracks. These tracks, with a diameter of 2 to 15 nanometres and spanning tens of micrometres in length, can be created under fully controlled conditions in large accelerators.

SHIs can replicate high-energy particle damage, such as that induced by cosmic rays or fission fragments making them invaluable for studying the properties, formation, and annealing mechanisms of those types of radiation damage in diverse materials. In earth science, fission track dating is routinely employed for geo- and thermochronology in minerals, such as apatite and zircon, to correlate the number-density, length and size distribution of tracks with the present uranium content to infer the age of rocks. Due to the complex nature in measuring detailed structural properties of ion tracks, there are still many open questions related to the exact mechanisms underlying the track formation process.

While the influence of the irradiation parameters on a wide range of materials have been studied to some detail, the question if and how the crystal structure of the host material locally determines the track morphology has rarely been addressed. As the physical as well as structural properties are a function of the crystallographic direction <uvw> in single-crystals, it is likely that ion track formation in most crystalline materials lead to anisotropic shapes of the track cross-section. Additionally, variations in track morphology along distinct <uvw> and the extent of these variances when comparing tracks created in different directions should also mirror the crystal symmetries and associated physical properties.

Previous work has demonstrated that synchrotron-based small angle X-ray scattering (SAXS) is highly suitable for investigating the structural details of ion tracks with extremely high precision averaging out fluctuations on the atomic scale by measuring ∼107 ion tracks generated under identical conditions. This precision enables to assess the anisotropy in the damage profile produced by SHIs.

In this talk, I will present how I utilised synchrotron-based SAXS to precisely quantify the structural anisotropy of the complete ion track cross-section in gemstone quality Durango fluorapatite (Ca5(PO4)3(F,Cl,OH)) as well as quartz (SiO2).  These findings enable to correlate structural properties of the  matrix material with ion track characteristics, revealing the influence of the local crystal structure on track formation, and are thus of significant interest across several different scientific areas, such as materials science and engineering, nanotechnology, geology and archaeology, interplanetary science, and nuclear physics.

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