Radiating Arrowheads Helps Retrace Indian Trade Routes

POCATELLO, Idaho (AP) — Idaho State University anthropologists are retracing American Indian trade routes by bombarding arrowheads and other stone tools with radiation that helps locate their origins.

The work at the Idaho Accelerator Center in Pocatello involves a process called photon activation analysis. It allows researchers to measure trace elements in an object and use the data to match artifacts with their places of origin, such as matching arrowheads made of obsidian with the lava flows they came from. That can provide evidence about how such items were passed among the West's tribes.

"This is the only accelerator center in the world doing this kind of work,'' ISU anthropology professor Herb Maschner told the Idaho State Journal.

The same results can be gained by drilling holes into the artifacts and irradiating them inside nuclear reactors, Maschner said. But that means the artifacts must be treated as nuclear waste afterward. The photo activation method causes no damage, he said.

The university's physics and anthropology departments began collaborating on the project about two years ago. Maschner wanted to trace the origins of the artifacts found by anthropologist and tribal members in the Aleutian Islands, and former Idaho Accelerator Center Director Frank Harmon told the professor he had a technique that could work without destroying the objects.

Maschner and Harmon began their project by irradiating rocks to see if they could get an elemental fingerprint. When they found the process worked, they added quality controls and did a little fine-tuning before starting on the artifacts.

Buck Benson, an ISU graduate student and Maschner's assistant, said the scientists experimented with obsidian and rocks from the lava flows in southeastern Idaho, discovering they could accurately match samples to particular flows.

The scientists know the obsidian in Maschner's arrowheads came from particular volcanos in Alaska, but they hope to learn which arrowheads correspond with which volcanos.

Their project uses a medical grade accelerator designed for cancer therapy. It shoots 25 million volts of electricity into a block that converts the current into gamma rays before it passes through the stone artifacts, which rotate in small containers on a turntable for a period of four hours.

"It changes the composition slightly to make them radioactive so we can measure the elements,'' Maschner said.

Afterward, the objects are set aside for a few days until they are radiation free. They can then be returned to the tribes.

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