About
The OSU Radiation Center is home to an active program in Archaeometry. We specialize in Instrumental Neutron Activation Analysis (INAA) to provide sensitive, high precision, multi-element characterization of artifact composition for archaeological research and conservation.
INAA can assist with:
Artifact Provenance Determination - link artifacts to their source based on the unique geochemical signature of the raw material, including ceramic clays, obsidian, or chert.
Authentication - verify authenticity or antiquity based on trace-element composition in comparison with ancient or modern materials.
Assessing Ancient Technology - utilize trace-element composition to infer technological processes and identify raw materials and alloys.
Advantages of INAA as an analytic technique:
- Scope - Sixty-seven common and rare earth elements become radioactive when exposed to the neutron flux in a reactor. Of these 67 elements, over 50 can be identified and measured quite readily.
- Multi-element - By using different combinations of irradiation and decay times, it is possible to measure a large number of elements from isotopes of different activities and half-lives. Our standard analysis package routinely provides an artifact “signature” of 32 elements.
- Excellent sensitivity - The INAA method permits measurement of all detectable elements with great sensitivity; many elemental concentrations are measurable in parts per million (ppm) or parts per billion (ppb).
- Elemental analysis - INAA determines element concentrations regardless of chemical form or oxidation state (e.g., ferric vs. ferrous iron).
- Non-destructive - Unlike other techniques, the sample is not destroyed by the analysis and can be re-irradiation and re-analyzed if necessary.
- Bulk analysis technique - For complex, heterogeneous materials such as pottery, it is often advantageous to characterize the entire ceramic body, rather than just the surface (e.g., XRF) or constituent inclusions (LA-ICP-MS). Conversely, we often combine INAA with visual methods of analysis, such as petrography, to help determine what is contributing to the bulk elemental signature of a sample.
Just what are we measuring so precisely?
With compositional studies of archaeological artifacts, we need to simultaneously assess variation from three sources:
- Natural variation in material resource or “parent material”, as well as variation resulting from environmental forces including erosion, redeposition, and weathering.
- Culturally induced variation, such as human manipulation of raw materials during manufacture of the artifact.
- Post-depositional modification by environmental factors once the artifact has been incorporated into the archaeological record.
The significance of these three sources of variation depends on our research question and on the type of material we are analyzing. Two common material types, obsidian and ceramics, demonstrate how these factors support or potentially confound the successful determination of artifact provenance.
Factors affecting obsidian composition:
As a form of volcanic glass, the chemical composition of obsidian reflects the mineralogy of the magma – the rock minerals melted under extreme heat and pressure to form molten lava. As volcanos evolve, the composition of their magma changes, so each eruption potentially generates a unique elemental signature. As a result, individual obsidian flows are highly homogenous in composition, with order-of-magnitude differences in composition between flows.
Cultural utilization of obsidian through knapping has no known impact on its composition, while post-depositional changes are limited to weathering (hydration) of exposed surfaces that can be removed prior to analysis.
Throughout, the unique compositional signature of the obsidian flow is preserved such that obsidian artifacts can be easily linked to a discrete geographic source.
Factors affecting ceramic composition:
Ceramics are a much more complex situation. Clays initially inherit their chemical composition from the weathering of silica-rich rock minerals. But natural factors such as erosion, redeposition, grain-size sorting, and chemical weathering can strongly modify and/or mix those signatures, creating clinal variation in composition, and making it difficult to distinguish closely spaced clay sources.
Further, clays are the ultimate “plastic” raw material: potters typically modify natural clays through sorting, sifting, refining, mixing, or the addition of temper to create ceramic pastes suitable for different wares and vessel functions. All these steps potentially confound the natural compositional signal. And once ceramics have been discarded, they are potentially subject to contamination from ground water and chemical pollutants.
Provenance determination of ceramics is therefore much more challenging, often requiring clay surveys to clarify the scale and nature of natural variation, paired with analyses of production debris or kiln waters to assess the degree of cultural modification.
The measurement capabilities of INAA offer a critical advantage here. The multi-element capability of INAA, combined with its high sensitivity, excellent precision, and accuracy, allows us to tease apart the complex chemical signatures and identify distinct sources of ceramic production.
See some of our current research projects in Mexico and Mesopotamia!
For additional information on our INAA services, please contact:
Dr. Leah Minc
541-737-4216
100 Radiation Center
Oregon State University
Corvallis, OR 97331