High Resolution X-Ray Computed Tomography Pathfinder Tests

AbstraktAbstract

The main technical objective of the activity is optimization of HR XCT (high-resolution X-ray computed tomography) scanning hardware and methodology for high-resolution and material-sensitive analysis of samples collected by the Pathfinder rover on the surface of Mars. The samples, that can be generally assumed to be geologic, will be provided in sealed tubular containers made of titanium grade 5 with diameter of 15 mm and wall thickness of 0.7 mm. The overall length of the sample container is 150 mm, however, only 60 – 70 mm will be filled. Currently, a typical laboratory HR XCT scanner utilises a cone-beam scanning geometry. An X-ray tube, which behaves as a point-like source of the X-ray photons, provides a divergent polychromatic beam that irradiates the sample and the detector unit. Thanks to the beam divergence, the radiographic image of the sample is magnified and consequently, the spatial resolution of the obtained image can be much higher than pixel spacing of the detector. Consequently, spatial resolution below 10 µm can be achieved, regardless of the detector pixel size. The key parameters are the width of the detector in pixels and the focal spot of the source. While the first defines the number of sampling points across the sample diameter, the latter limits the maximal spatial resolution of the imaging system which is limited by the penumbra effect. Considering that the-state-of-the art X-ray digital detector typically provides a width of approximately 2000 pixels or more and that the standard micro-focus tube has focal spot in a range of micrometres (best possible resolution is ~ ⅔ of the spot size), reaching the single-digit micron resolution for the given samples with diameter of 15 mm is possible.

The main technical objective of the activity is optimization of HR XCT (high-resolution X-ray computed tomography) scanning hardware and methodology for high-resolution and material-sensitive analysis of samples collected by the Pathfinder rover on the surface of Mars. The samples, that can be generally assumed to be geologic, will be provided in sealed tubular containers made of titanium grade 5 with diameter of 15 mm and wall thickness of 0.7 mm. The overall length of the sample container is 150 mm, however, only 60 – 70 mm will be filled. Currently, a typical laboratory HR XCT scanner utilises a cone-beam scanning geometry. An X-ray tube, which behaves as a point-like source of the X-ray photons, provides a divergent polychromatic beam that irradiates the sample and the detector unit. Thanks to the beam divergence, the radiographic image of the sample is magnified and consequently, the spatial resolution of the obtained image can be much higher than pixel spacing of the detector. Consequently, spatial resolution below 10 µm can be achieved, regardless of the detector pixel size. The key parameters are the width of the detector in pixels and the focal spot of the source. While the first defines the number of sampling points across the sample diameter, the latter limits the maximal spatial resolution of the imaging system which is limited by the penumbra effect. Considering that the-state-of-the art X-ray digital detector typically provides a width of approximately 2000 pixels or more and that the standard micro-focus tube has focal spot in a range of micrometres (best possible resolution is ~ ⅔ of the spot size), reaching the single-digit micron resolution for the given samples with diameter of 15 mm is possible.