Neutron Imaging Uncovers Precious Gem Formation

An international research collaboration, including scientists from the UK, Italy, Japan and the USA, has used the IMAT instrument at STFC’s ISIS neutron and muon source to study the inner form of the pearl. This non-destructive neutron technique could be used to help differentiate between highly valuable naturally-formed pearls from farm-cultured varieties.

The IMAT was used to bombard the entire pearl sample with 5.9 million neutrons per second and a powerful camera then mapped the neutrons to build a detailed tomographic reconstruction of the pearl.

IMAT scientist Dr Winfried Kockelmann said: “By utilising the unique capabilities of the new neutron imaging instrument we are able to non-invasively study pearls and other precious objects and build microstructure maps of their interiors, in addition to the usual neutron CT images produced on IMAT.

“We hope that by studying the differences between cultured pearls, like the soufflé and its naturally-occurring rivals, we will be able to come up with a quick and easy test to establish whether a pearl has been cultured or not.”

Giuseppe Vitucci from the Italian team at the University of Milano-Bicocca said: “Despite their well-known tiny aspect, each pearl hides tons of peculiarities in its morphology, as well as in its atomic composition, some of which cannot be detected using the standard x-ray technology. By contrast, the cold neutron pulses available at the IMAT beamline, together with the new energy-resolving detection system, may reveal such ‘cool’ secrets. No pun intended.”

During this investigation, an X-ray image was also taken of this cultured pearl for comparison. While the vacuum core and irregular morphology were distinguishable, further details of this sample were not easily recognisable using X-ray alone.

Neutron imaging cannot compete with the resolution of X-ray imaging but it does have several other advantages. As neutrons are electrically neutral they interact weakly with most materials and therefore penetrate them deeply. Additionally, neutrons are highly sensitive to certain elements that X-rays aren’t, such as hydrogen, due to their large neutron scattering cross sections. Neutrons are also able to distinguish between isotopes of the same element as, unlike X-rays, they interact with the nucleus of the atom.

IMAT scientist Dr Triestino Minniti added: “In this study the key point is the connection of the specimen morphology, obtained non-destructively by means of a neutron CT scan, with its mineralogy and microstructure properties. For the latter, a precise definition of the materials lattice parameters are required that could only be obtained with sufficient resolution at a neutron imaging instrument like IMAT at ISIS, rather than one located at a steady-state neutron source.”

Further investigations using neutrons of different energy ranges may allow a more complete description of similar biological samples and form the basis for upcoming work at the facility.

Despite the fact that IMAT is still undergoing commissioning, this instrument is already showcasing the potential of neutron imaging as an innovative tool to study biological samples. The future applications of this young imaging and diffraction instrument are expected to span a variety of industries from aerospace to earth science.

*G. Vitucci, T. Minniti, D. Di Martino, M. Musa, L. Gori, D. Micieli, W. Kockelmann, K. Watanabe, A.S. Tremsin, G. Gorini , Energy-resolved neutron tomography of an unconventional cultured pearl at a pulsed spallation source using a microchannel plate camera. Microchemical Journal Volume 137, March 2018, Pages 473-479, doi:10.1016/j.microc.2017.12.002.