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Sample preparation guideline

SRXTM at XTM beamline is based on microtomography geometry with an available x-ray energy range of   5 – 15 keV.  To obtain the best imaging quality, the sample must be fixed or stabilized to make sure that there is no displacement during tomographic imaging. We highly recommend the samples be prepared in a cylindrical shape to minimize the imaging artifacts. For inorganic samples (composed of Ca, Cu, Se, Fe, Zn, etc.) or higly absorbe x-rays, the size should be less than 3 mm in diameter. However, for other samples that are composed of organic elements (C, H, O, N) or poorly absorb x-rays, the size can be up to 10 mm in diameter.  SRXTM at XTM beamline is not suitable for larger samples, alloys, or titanium composites due to limited x-ray energy. Feasible samples are listed below unless stated otherwise.

SIZE of the sample

For an optimal absorption contrast, the x-ray images are aimed to obtain at 30% transmission (or 70% absorption). The absorption of X-rays by a sample depends on the quality of the X-ray beam, the elemental composition in the sample as well as the density and thickness of this sample. In general, the sample should be aligned within the FOV during rotation. This mean that the appropriate sample must be smaller than the FOV listed in the optical performance table.  For example, to obtain the highest-resolution images with the pixel size of 0.72 micron, the diameter or thickness of the sample must not exceed 1.7 mm. Unless it contains mostly organic compounds and/or poorly absorbs x-rays, the sample can be larger than FOV.  

In case of sample larger than FOV, the tomography dataset will be acquired from concatenated scans following the image stitching procedure. The experiment should be setup carefully to avoid misalignment that would affect the tomographic calculation. Also, the increased data volume should be taken into account.  

For further analysis such as % porosity or pore distribution, we recommend that the sample should be >10-times larger than the selected feature to justify the analysis.  For example, to determine the porosity, a bone sample with an average pore size of 100 microns should be prepared in 2 - 3 mm in diameter. 

SHAPE of the sample

Cylindrical shaped sample is the most preferrable sample to x-ray tomography.  According to the experimental setup, the x-ray beam is perpendicular to the rotation axis, the cylindrical shaped sample will give the constant pathlength (the width) during the sample rotation. This satisfies the back projection algorithm in tomographic reconstruction.  In case of laminate sample, the pathlength will vary during rotation.   Particularly when it turns the maximum width to the x-ray beam, it could give 0% transmission that disturbs the back projection algorithm.  If it is possible, we suggest preparing the sample into a stick as illustrated.   

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laminate_sample.png
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Laminate sample should be cut to a stick. 

List of feasible samples 
(size in thickness or diameter)

Bones, scaffolds

  • Spongy bone < 5 mm

  • Compact bone < 3 mm

Fiber, Hair, Fabrics

Cellulose

Silk

Hair

Tooth

Less than 1 mm

Fruit seed, rice, maize

Rice ​3  mm 

Seed 3 - 5 mm

Wood, stem, pollen

Wood 3 - 5 mm

Stem  3 - 5 mm

Rock, Gem

Limestone/Shale 1 - 2 mm

Microfossils  < 3 mm

Gem stone < 3 mm

Pearl 1 mm

​

Insects

  • Flies (fixed in EtOH, air dried)

  • Worm (fixed in EtOH, air dried)

Polymers, Rubbers

PLA 3 -5 mm

PP 3 - 5 mm

Composites; PVDF 3 - 5 mm

Geopolymer < 3 mm

Ceramic < 2 mm

Soils, clays

Soils 

Clays < 3 mm

Size of the sample
List of feasible samples 
Shape of the sample

Available sample holders & tools​ 

Experiment_edited.png
Experiment

Experiment

Sample Preparation

Fixation

  • Using formaldehyde (FA) or glutaraldehyde (GA)

  • Typical 4% is used, for 12 hours or more

Dehydration & immerse

  • 70% EtOH, 2 hours

  • 80% EtOH, 2 hours

  • 90% EtOH, 2 hours

  • 100% EtOH, 2 hours

  • Immerse inHexamethyldisilazane (HMDS), 2 hours

Air dry

Make or become dry through contact with unheated air  minimum 2 hours

Handling & Mounting

  • Available specimen carrier and Goniometer head

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  • Sample holder options at BL1.2W

    1. 45° Mount,  Ø = 6 mm, aluminum

    2. 45° and 90° Mount, Ø = 6 mm, aluminum

    3. 90° Mount , Ø = 6 mm , aluminum

    4. Ø = 6 mm , aluminum

    5. Ø = 1.5 mm, brass

  • Handling and mounting use container density less than sample density. Often used are small polystyrene tubes

  • In order to mount the sample to sample holder use transparent glue, wax or 2-side tape

  • User should make sure that the sample is stabilized to the sample holder other wise sample displacement during data collection will affect the CT reconstruction

Sample preparation.jpg

Other apparatus that may be needed in sample preparation e.g. heat gun, glue gun, and stereo microscope, are also provided at the Sample Station

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