Space mission shows Earth's water may be from asteroids: study NatureAstronomy
) that was 20 µm thick, a CMOS camera that had 2,048 × 2,048 pixels and a ×20 lens. The pixel size of the NH mode was ~0.25 µm and the FOV was ~0.5 mm. The detector for XRD mode was equipped with a scintillator consisting of a P43 powder screen that was 50 µm thick, a CMOS camera that had 2,304 × 2,304 pixels and relay lenses. The effective pixel size of the detector was 19.05 µm and the FOV was 43.9 mm.
For the XRD mode, an X-ray beam was focused by a Fresnel zone plate. With this mode, the detector was located 110 mm behind the sample, with a beam stop 3 mm in front of the detector. Diffraction images of 2ranging from 1.43° to 18.00° were acquired with an X-ray beam spot focusing on the bottom of the FOV of the detector. Samples were vertically translated with a certain interval, and a half-rotated for each vertical scan step.
. The SR-XRD-CT analytical conditions were almost the same as for the SR-XRD analyses. For the XRD-CT mode, the detector was located 69 mm behind the sample. Diffraction images of 2ranging from 1.2° to 17.68° were acquired with both an X-ray beam and a beam stop that were placed on a straight line to the centre of the FOV of the detector. The sample was scanned horizontally with 180° rotation of the sample.
The X-ray energy was fixed to 30 keV for all experiments because it is the lower limit for X-ray penetration of meteorites that are ~6 mm in diameter. The number of images acquired for all CT measurements during the 180° rotation was 1,800 , and the exposure time for images was 100 ms for the WL mode, 300 ms for the NH mode, 500 ms for XRD and 50 ms for XRD-CT. The typical scanning time for one sample was ~10 min in the WL mode, ~15 min in the NH mode, ~ 3 h for XRD, and 8 h for SR-XRD-CT.
CT images were reconstructed by a convolution-backprojection method and normalized for linear attenuation coefficients of 0 to 80 cm. Slice software was applied for the analysis of 3D data, and muXRD software was used for the analysis of XRD data.The epoxy-mounted Ryugu particles were polished on a surface in a stepwise manner down to the level of a 0.5 µm diamond lapping film under dry conditions avoiding elution of any materials from the surface during polishing.
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