PIXE spectrometry is a powerful analytical
tool that is used extensively in research as diverse as the study of the mobility of environmental
pollutants, the tracking of trace element build-up during the onset of health disorders, and the
identification of variability of ink recipes used in the printing of medieval bibles. Penn Museum and
the Bartol Research Institute of the University of Delaware have collaborated over the past two
decades, to refine PIXE spectrometry for application to the characterization of ancient materials,
in part to track the chronological development of early copper-, steel, and glass-making, and in
part to document novel features of early goldworking practices, such as gilding and soldering.
Left: Dr. Charles P. Swann adjusts the proton beam alignment on the PIXE unit at the
Bartol Research Institute of the University of Delaware.
PRACTICAL ASPECTS OF PIXE SPECTROMETRY
When a material is bombarded by protons, several kinds of atomic reactions occur, among them the
displacement of electrons out of their orbits in individual atoms. As each disturbed atom recovers
its stability, it emits a group of x-rays which in their energies characterize the element from
which they originate, and in their intensities are proportional to the concentration of that element.
The composition of the material overall is thus represented by a multi-peaked spectra that provide
simultaneously the constituents of the "recipe" for an artifact's production-e.g., how much tin was
added to copper to make bronze-and the minor and trace elements which may be indicate a metal's
provenance or explain a glass's source of coloration.
A number of features, practical and theoretical, make PIXE spectrometry particularly
valuable in the study of ancient artifacts:
. It is essentially non-destructive, usually requiring only that the artifact's
surface be lightly abraded, to remove corrosion or grime.
. For well established reasons that relate to the way protons interact with matter,
it is very sensitive in the measurement of trace elements, often with detection limits that are an order-of-magnitude
better than those obtainable by other analytical techniques of materials analysis, such as x-ray
fluorescence (XRF) and scanning electron microscopy (SEM/EDAX).
. When operated in a "microbeam mode" (i.e., with a spatial resolution of about a
twentieth of millimeter), it can be used to study individual parts of an complex artifact such
as a item of highly decorated gold jewelry, an ore of mixed minerals, or a remnant of smelting slag.
. Since the artifact does not have to be put into any kind of special vacuum chamber
during analysis, it is a convenient way to gather data about an artifact, such as a bronze
statuette or a gold plaque, before it is included in an exhibition display.
A limited number of reprints are available on the technical aspects of PIXE Spectrometry as
applied to archaeological materials, including:
Detection Limits for Copper
Detection Limits for Glass
Some of the publictions that have resulted from this collaboration are abstracted below.
For questions on content and/or availability of reprints, please contact Stuart Fleming
Distinguishing Between Native and Smelted Coppers using PIXE Spectrometry: A Case History from Early Colonial America
Metal-forming Practices among the Seventeenth Century Illinois, 1640-1682
Confounding the Conquistadors: Tumbaga's Spurious Luster
Roman Mosaic Glass: A Study of Production Processes, using PIXE Spectrometry
Roman Influences on Metalworking at the Titelberg (Luxembourg): Compositional Studies using PIXE Spectrometry
Recent Applications of PIXE Spectrometry in Archaeology: Observations on the Early Development of Copper Metallurgy in the Old World
Recent Applications of PIXE Spectrometry in Archaeology: Characterization of Bronzes with Special Consideration of the Influence of Corrosion Processes on Data Reliability
Recent Applications of PIXE Spectrometry in Archaeology: Characterization of Chinese Pottery Exported to the Islamic World
A Bronze Figure of Tutankhamun: Technical Studies