Materials

aRTist approximates the X-ray attenuation coefficients of chemical compounds from the attenuation properties of their single chemical elements. It uses the elementary mass attenuation coefficients from the Evaluated Nuclear Data File (ENDF). Higher-order structural effects such as the electron band structure of crystals or the orbital configurations of molecules are not taken into account. Any material is simulated as “the sum of its elementary parts.”

Note

We continue with the project from the last tutorial. You can download it here if you need the current state:

tutorial_positioning.aRTist (4.6 MB)

Materials Editor

aRTist has a built-in materials editor (Fig. 65) that helps you manage your library of materials. You can change and add entries there, and inspect the attenuation coefficients that aRTist has calculated.

Note

In the toolbar, click the button Edit material properties or open it from the Menu bar: Tools → Materials…

Fig. 65 Materials Editor

We will create a simple glass ceramic that has the following composition:

• Al₂O₃ with a mass fraction of 40%

• SiO₂ with a mass fraction of 60%

• Overall density: ρ = 2.53 g/cm³

In the materials editor, this compound would be represented as Al2O3 0.4 SiO2 0.6. Each of the two components is written in its empirical formula, using the chemical symbols from the periodic table of elements, followed by the number of atoms. After a compound, its mass fraction may follow (separated by a space from the empirical formula). The mass fractions will be automatically normalized to their total sum. For example, Al2O3 40 SiO2 60 would represent the same material as above.

Note

In the Materials Editor, click on Add new material definition. An empty row will appear where you can fill in the new material information (Fig. 66).

1. Enter a material name, e.g. Glass Ceramic.

2. Enter the density: 2.53.

3. Enter the composition: Al2O3 0.4 SiO2 0.6.

4. You may also add a comment, if you want.

Click Apply to save the list.

Fig. 66 We add the glass ceramic as a new material.

It is important to click Apply to save the changes you have made. The button Refresh will re-load the internal library, delete any unsaved changes you have made, and show changes that other aRTist modules have made in the material library in the time since you have opened the Materials Editor.

Attenuation Data Viewer

For each material, you can display the attenuation data that aRTist will use during the simulation.

Note

Make sure that our Glass Ceramic is selected in the Materials Editor and click on .

The Attenuation Viewer (Fig. 67) will appear and show a plot of the attenuation coefficients.

Fig. 67 The attenuation viewer shows a plot of the attenuation coefficients.

If you want to display a different photon energy range, you can enter it in the upper part of the window: min. energy and max. energy. The plot displays five curves that represent the following:

The total attenuation coefficients are plotted as a black line and consider all the modelled effects from particle physics.

The contribution from the photo effect (photoelectric absorption) is plotted as a blue line.

The contribution from incoherent scattering (Compton scattering) is plotted as a red line.

The contribution from coherent scattering (Rayleigh/Thomson scattering) is plotted as a green line.

The contribution from pair production (purple line) becomes relevant at photon energies above twice the electron rest mass: h⋅f > 2 m_ec² (1.022 MeV).

Note

Switch to the Text tab to display the data as a text table. (Fig. 68)

Fig. 68 The calculated data points for the attenuation coefficients are shown in a text table.

You can save the attenuation data as a text file with the Save button in the upper right corner of the Attenuation Viewer.

Note

Close the Attenuation Viewer and the Materials Editor.

Setting the Material of a Part

We now want to set the Rotor’s material to the Glass Ceramic that we have created. You can do this in the Material column in the Assembly List.

Note

Click on the current Material of the Rotor (should be Fe). From the list, choose the Glass Ceramic that we have created. (Fig. 69)

Fig. 69 We set the Glass Ceramic as the Rotor’s material.

The attenuation behaviour of the Rotor should now change and represent the one of the Glass Ceramic. The grey values in the projection’s preview image will become lighter as the Glass Ceramic absorbs less radiation than iron.

Summary

In this brief tutorial you have learned how to manage your materials library, set the material of a part and how to access its attenuation coefficients.

The scene that we created up to this point is available for download:

tutorial_materials.aRTist (4.6 MB)