Good morning.
I'm analyzing a Tomography (CT) of a ancient metallic artifact. This sample has 2 materials (i determinate this using XRF) one is mostly iron and the other mostly copper. But when i analyze the grey scale. The copper part is more (white) pale that the iron part. The empty zones are black. So i think that the iron part should be more brigth that copper, because the iron density is higher.
If you can explain me this i really appreciate it.
Thanks
Dear Rafael Campo ,
CT primarily delivers the mean linear attenuation coefficient (µ), which is the product of the x-ray mass-attenuation coefficient (µ/rho) and the density (rho):
µ=(µ/rho)*rho.
By the way: in contrast to your statement from above, bulk Copper (rhoCu ~ 8,96g/cm³) has got higher density than Fe (rhoFe ~ 7,87g/cm³) and in addition Cu has got higher atomic number, which also leads to higher mass-attenuation coefficient compared to Iron .
You should now draw new conclusions.....
However, please check the possibility of partial volume effects; i.e. whether your metallic parts are smaller*) in (at least) one of the lateral dimensions compared to the lateral resolution of your CT system. In this case you will get the mean density of the metal part be under-estimated for such special voxels and you will have some kind of effective mean density rhoeff, which will be smaller than the mean bulk value ( rhoeff < rho).
For these special voxels this will cause severe consequences in the effective µeff:
µeff = (µ/rho)*rhoeff
Please note that the mean (µ/rho) value is a material constant and is not affected by partial volume issues.
*) such as for example small thin flakes or even thin wires or even the rim of the metallic parts of your sample
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