The computerized X-ray microtomography laboratory of the National Institute of Geophysics and Volcanology deals with the study of natural phenomena in contexts of volcanic and seismic risk (vesiculation mechanisms, crystallization and magmatic fragmentation, propagation of fractures, circulation of fluids, processes of alteration, etc.). Present within the Vesuvius Observatory of Naples (OV-INGV), it is coordinated by the researcher Lucia Pappalardo, to whom we asked:
What is microtomography?
"Tomos" in Greek means to cut, to dissect, and tomography is precisely a technique for making virtual cuts in an object through the use of X-rays to highlight its internal structure.
How does it work?
Microtomography is a technique very similar to CT performed in the hospital: however, while in CT the patient is stationary and the X-ray sources rotate, in the case of computerized X-ray microtomography the detector and source are fixed and moving is the sample, mounted on a rotating stage. At various rotation steps, radiographs (projections) of the object are acquired on a regular basis with a digital detector and the set of projections (sinogram) is processed using mathematical algorithms to reconstruct a virtual three-dimensional image of the sample.
Is the term micro used because we are talking about microscopic measurements?
We speak of microtomography precisely because the spatial resolution is of the order of the fraction of a micron up to a few tens of microns, while in CT the resolution is of the fraction of a millimetre.
What use is made in Geosciences?
X-ray microtomography (micro-ct) applied to geosciences allows the qualitative and quantitative study of the internal structure of rocks and other geomaterials; in the last decade, in fact, this technique has become an essential part of research in various sectors (planetary geology, mineral and oil fields, hydrogeology, sedimentology, structural geology, environmental geology, etc.). One of the advantages of this technique is the possibility of studying the internal characteristics of rocks up to very high resolution (for example orientation and distribution of fractures, pores, grains, minerals, sedimentary structures, fossils, fluid inclusions, etc.) without damaging them.
What are the priorities of your research activity?
Very important in this context is the determination of the microstructure (porosity, permeability, shape and distribution of crystals and vesicles, etc.) of volcanic rocks, as the determined textural parameters allow to investigate the mechanisms and times of degassing and magmatic crystallization which they accompany the opening and propagation of volcanic conduits before eruptions. Understanding these processes is essential to better interpret the geochemical and geophysical phenomena recorded on the surface by the monitoring networks during the pre-eruptive crises.
Gallery – Lucia Pappalardo at work in the computerized X-ray Microtomography laboratory