An x-ray computed tomography scanner has been used in an attempt to look at the pore space of a limestone rock sample (a carbonate, $\ce{CaCO3}$) saturated with a $\mathrm{12\ wt\%}$ sodium iodide ($\ce{NaI}$) solution as the x-ray dopant.

The idea is that the sodium iodide would absorb the x-rays more so than the grain matrix of the rock and thus the fluid in the pore space of the rock can be seen, by contrast in x-ray absorption. Therefore, the primary entity that is measured through CT scanning is x-ray absorption, defined as the attenuation coefficient. This is determined both by mass density and elemental composition of the material.

Unfortunately, this doped fluid wasn't able to be seen. Next tests will use a chalk (composed ~90% or greater of $\ce{CaCO3}$). Typically for tests of this nature sodium iodide is preferred because its interaction with sorts of clay is similar to that of sodium chloride.

The questions are:

  1. What is the highest attainable concentration of a sodium iodide solution?
  2. It is known that a solution of barium chloride has been used an x-ray dopant. Would this solution be compatible with chalk, i.e. non-reactive with chalk? What would its highest attainable concentration be?
  3. What other possible solutions can be used as x-ray dopants?

NIST has values of mass attenuation coefficients by element and provides a very useful tool for looking up the specific attenuation coefficient for mixtures.

My quest is to understand what x-ray dopant solutions are possible and what their highest concentrations achievable are. Then to rule out ones that are reactive with the rock.

  • $\begingroup$ How much pore space is there? $\endgroup$ – Abel Friedman Dec 10 '14 at 22:52
  • $\begingroup$ for this particular core it was estimated to be ~13% $\endgroup$ – Armadillo Dec 10 '14 at 23:05
  • $\begingroup$ Try to increase the concentration first. NaI has quite high solubility. Hopefully, it would be enough. $\endgroup$ – permeakra Dec 11 '14 at 23:58

This is just me shooting bull because I don't know what has been done, but in the distant past, mineralogists used concentrated solutions of heavy metal salts for density determination by flotation. Clerici's solution is a solution of equal parts thallium malonate and thallium formiate in water. That may just be the ticket.

Also, those with access to appropiate protective gear (i.e. fume hood and proper gloves) may consider methyl iodide.

  • $\begingroup$ Methylene iodide is even better. $\endgroup$ – Ivan Neretin Sep 6 '17 at 7:21

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