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Rachel Popelka came to Mizzou to study because there was
no other place in the nation where she could do her research.
Photos by Chris Detrick
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Analyzing
Antiquities
By Nancy Moen
To dig up clues about past cultures, Rachel
Popelka produces chemical fingerprinting of archaeological specimens
to determine their source.
The doctoral student in chemistry
uses the Archaeometry Lab at the University
of Missouri Research Reactor (MURR) to unravel archaeological
problems. She analyzes the chemical composition of artifacts to
gather information that is unavailable through traditional archaeological
methods.
“The Archaeometry Lab is unique and
is one of the few places in the world where this kind of research
is done,” Popelka says. “One of the special things
about MURR is that, as a student, I can learn and work on such
specialized and powerful lab equipment.”
Given this unique toolbox of nuclear methods,
Popelka moves beyond the traditional archaeological techniques
she acquired as an undergraduate student and beyond her experience
at excavations in Italy, Jordan and Greece. She uses the technologies
on human-made materials such as ceramics, glass, pigments and
metals.
The Archaeometry Lab at the MU Research
Reactor Center has provided analysis for more than 72,000
archaeological specimens and gained a national and international
reputation since its founding in 1988. Pictured above is
the research reactor core.
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By learning the chemical basis of sources
of artifacts, Popelka gains insight into ancient cultures and
ancient technology as well as answers to such mysteries as the
sources of ancient glass beads and the paths of ancient trade
routes.
Two processes — laser ablation inductively
coupled plasma mass spectrometry (LA-ICP-MS) and neutron activation
analysis (NAA) — provide the clues she needs.
Through LA-ICP-MS, Popelka uses a laser to
analyze tiny amounts of an artifact for the composition of trace
elements. The technique is especially useful on small artifacts
because it does minimal damage. NAA gives data on trace elements
by bombarding a sample with neutrons and causing various nuclear
reactions. As the products decay, they emit gamma rays that identify
which elements are present.
When she understands the patterns of trace
elements, Popelka possesses a sort of fingerprint that helps identify
artifacts and the sources of raw materials in them. The analysis
can distinguish among visually similar ceramics that are produced
in geographically different locations.
Professor Dave Robertson works with Popelka
as her adviser in chemistry and is clearly impressed with the
quality of his only student in such an unusual research area.
Popelka not only uses the analytical methods that are available;
she creates new ones, too.
“She knows what she’s interested
in, and she’s good at it,” Robertson says. “When
MU can attract a student of Rachel’s quality, everyone should
feel good.”
By identifying the composition of these ancient glass beads
through nuclear analysis, Popelka can determine their origin.
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Popelka recently won a National
Science Foundation Graduate Research Fellowship, which recognizes
her superior scholarship and great promise as a future researcher
and teacher.
In a current project, Popelka is conducting
tests on more than 1,000 ancient glass beads collected from sites
throughout Africa.
From her anthropological research, she knows
that glass beads dating to two to three millennia ago have been
found at numerous archaeological sites in sub-Saharan Africa.
People of that time valued the beads of various colors, shapes
and sizes both as artistic expression and as currency.
Anthropologists have long assumed that African
beads dating before European contact were manufactured in India
and brought to Africa by maritime trade. Because many of the beads
look similar, attempts to identify their source of manufacture
through color and shape alone have been inconclusive.
Senior Research Scientist Michael
Glascock considers Popelka to be a consummate scholar, one
who seeks enlightenment, not just a degree.
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That’s where archaeometry comes in.
Through nuclear analysis, Popelka can determine whether the chemical
composition contains alkali (soda) from potash through potassium-rich
plants such as trees and ferns; alkali derived from natron, mineral
deposits commonly found in marine areas; or alkali from trona,
which originates from the ashes of desert or marsh plants.
With more than 500 samples tested, she and
her collaborators have found trends in the color chemistry and
association of elements and have identified two major types of
ancient glass. Ultimately, that information will help determine
the origin of the beads and possibly some trade patterns of the
past between Africa and India.
Note: This story was published originally
in the winter 2005 issue of Mosaics, the magazine for alumni
and friends of the College of Arts and Science.
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Last Update:
November 15, 2007
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