In an interview by Karen Thomas with the International Society for Optics and Photonics (SPIE), APS user Stuart Stock (Northwestern University) discusses how x-ray diffraction reveals details of mummified remains.
Stuart Stock is a research professor of cell and developmental biology at Northwestern University (NU).
In 2018, NU's Block Museum of Art held an exhibit titled "Paint the Eyes Softer: Mummy Portraits from Roman Egypt." These portraits are especially important since few other paintings have survived from the Greco-Roman tradition. The centerpiece of the exhibit was the "Hawara Portrait Mummy Four" — a mummified child buried with a luminous painted portrait. University researchers used computed tomography (CT) to investigate subsurface deterioration and reveal details of the encased body and items within the wrappings.
Stock will be a plenary speaker at SPIE Optics + Photonics where he will cover the provenance of the mummy, what CT tells us about the person and object enclosed, and what secrets x-ray diffraction can reveal.
SPIE: You're known as one the pioneers of x-ray micro-computed tomography (microCT) and position-resolved microbeam x-ray diffraction. Could you describe these technologies and your role in developing them?
Stuart Stock: The first thing to understand is that I am not the person who makes new instruments. Instead, I think of myself as someone who looks at emerging imaging and diffraction technologies and imagines how they might be combined or used to study samples in novel ways. The mummy study described below is an example.
I have been using microCT since 1985, and, in fact, my first paper on the subject was in an SPIE proceedings (X-ray Imaging II, SPIE Vol. 691, 1986). In all forms of (x-ray) CT, one shines x-rays through an object from many different directions. The resulting set of radiographs are then mathematically recombined to give a 3D map of the contents of the object. As the prefix indicates, microCT is a microscopic version of clinical CT scanners.
I have been doing position resolved x-ray diffraction even longer than I have been doing microCT. In x-ray diffraction, a beam of x-rays scatters from the specimen, and crystalline materials reinforce the scattering in certain directions related to the periodicities of the atoms within the crystals. The resulting diffraction pattern is a kind of fingerprint of the material(s) encountered by the beam. In position-resolved x-ray diffraction, one makes a very narrow beam of x-rays, smaller than the diameter of a hair. One scans the beam across the sample and observes the resulting diffraction patterns. Typically, one uses synchrotron x-rays from a storage ring such as the Advanced Photon Source, but people also do this kind of mapping in their home laboratories.
Excerpt © 2021 SPIE
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