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Research

Low frequency electron paramagnetic resonance (LFEPR) spectroscopy

The laboratory is currently involved in a major project to develop LFEPR spectroscopy for studying objects with cultural heritage significance. LFEPR spectroscopy is a form of electron paramagnetic resonance (EPR) spectroscopy. Unlike EPR which can only examine objects less than ~125 mm3, LFEPR can examine objects of several liters in volume. Because of the size limitation of EPR, EPR of objects with cultural heritage significance is limited to shards or a sample of a larger object removed in the least invasive and destructive manner. Because LFEPR spectroscopy can accommodate much larger objects, it can be used to study intact large objects non invasively and non destructively. The image to the left is of a ~15 cm diameter, intact, Chinese Ming Dynasty bowl in our LFEPR spectrometer.

EPR spectroscopy is used to study paramagnetic materials such as transition metal atoms and stable free radicals. The ceramics, marble, pigments, and glazes found in cultural heritage objects may possess an EPR signal. These signals vary with the oxidation state and coordination of the metal atom. The signal can be used to identify the specific paramagnetic metal or stable free radical in the object. Since the availability of clays vary from region to region, the EPR signal may tell us the origin of a ceramic object.

Since the oxidation state and coordination of the metal can change with firing temperature of a ceramic object, so will the EPR signal. For example, the graph on the left presents the peak-to-peak absorption linewidth and peak-to-peak signal amplitude as a function of the firing temperature (TF) for kaolin clay. Information like this may be usable to determine TF of a ceramic object. Since higher firing temperatures increased with historic time, a determination of TF indirectly date an object. Knowing the composition of clay in an object as well as its firing temperature may allow us to confirm an object's provenance.

 

We are currently working the following LFEPR projects.

  • To understand the LFEPR signal as a function of firing temperature from Fe(III) fould outside of the aluminosilicate lattice. The iron in clay eists as an impurity in the aluminosilicate lattice, replacing some aluminum in the lattice, and as iron oxide located outside the lattice. The EPR signal from the iron outisde the lattice varies considerably with firing temperature.
  • To understand the LFEPR spectrum of Mn(II) in marble. The LFEPR signal of Mn(II) is very complex due to the large number of spectral transitions when the EPR frequency is comparable to the hyperfine interaction.
  • To develop a small volume surface coil probe. We believe such a pick-up coil can be used to study the pigments used in illuminated manuscripts.

 


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Magnetic Resonance Laboratory
Center for Imaging Sciecne
Rochester Institute of Technology
54 Lomb Memorial Drive, Rochester, NY 14623-5604

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