Scientists develop method to detect radioactive materials in gold, copper

Collision cell. (Image by Andrea Starr, courtesy of the Pacific Northwest National Laboratory).

Researchers at the US Department of Energy’s Pacific Northwest National Laboratory have developed a method that holds promise for transforming how ultra-trace elements are separated and detected.

Ultra-trace levels of radioactive materials can wreak havoc on sensitive equipment such as microchips, transistors, sensitive sensors, or instruments searching for evidence of currently undetected particles believed to comprise most of the universe. 

In a paper published in the Journal of Analytical Atomic Spectroscopy, the scientists said that low levels of troublesome naturally occurring radioactive elements like uranium and thorium atoms are often tucked among valuable metals like the gold and copper that go into the electrical components of circuits and other electronic instruments. So far, it has been extraordinarily difficult to tease out how much is found in samples of ore mined across the globe.  

The innovation can help further hone the chemistry that produces the world’s purest electroformed copper, pictured here. (Image by Andrea Starr, courtesy of the Pacific Northwest National Laboratory.

However, the team led by Khadouja Harouaka, Isaac Arnquist and Greg Eiden found a way to detect the radioactive traces by sending their samples through a series of isolation chambers in a collision cell.

These chambers first filter and then collide the rare atoms with simple oxygen, creating a “tagged” molecule of a unique molecular weight that can then be separated by its size and charge. 

The researchers said the effect is like finding a way to tie a helium balloon to each target thorium or uranium atom so that it floats above the sea of gold samples and can be counted with a mass spectrometer. 

In other words, in the collision cell chamber, charged atoms of thorium and uranium react with oxygen, increasing their molecular weight and allowing them to separate from other overlapping signals that can disguise their presence. 

“It is particularly difficult to measure low levels of thorium and uranium in precious metals like the gold that goes into the electrical components [of the most sensitive detectors in the world],” Harouaka said in a media statement.

“With this new technique, we can overcome that challenge and achieve detection limits as low as 10 parts per trillion in gold.”  

Besides helping eliminate unwanted and radioactive intruders in such detectors and things like integrated circuits, the innovation can help further hone the chemistry that produces the world’s purest electroformed copper.

This copper forms a key component of sensitive physics detectors, including those used for international nuclear treaty verification. 

More News