A D V A N C E D M A T E R I A L S & P R O C E S S E S | A P R I L 2 0 2 1 1 1 DETECTING ULTRA-TRACE ELEMENTS Chemists at the DOE’s Pacific Northwest National Laboratory (PNNL), Richland, Wash., developed a simple and reliable method that holds promise for transforming how ultra-trace elements are separated and detected. Low levels of naturally occurring radioactive elements like uranium and thorium atoms are often embedded in valuable metals like gold and copper. It has been extraordinarily difficult, impractical, or sometimes even impossible to tease out how much is found in samples of ore mined across the globe. Yet sourcing materials with very low levels of natural radiation is essential for certain types of sensitive instruments and detectors, like those searching for evidence of currently undetected particles that many PNNL scientists Khadouja Harouaka (seated), and Isaac Arnquist, prepare samples in an ultra-clean laboratory, which is necessary to ensure accurate mass spectrometry measurements. Courtesy of Andrea Starr/PNNL. physicists believe comprise most of the universe. Scientists locate extraordinarily rare atoms from the huge field of ordinary atoms by sending their samples through a series of isolation chambers. These chambers first filter and then collide the rare atoms with simple oxygen, creating a “tagged” molecule of a unique weight that can then be separated by its size and charge. In this case, the sophisticated counter is a mass spectrometer. The central innovation is the collision cell chamber, where charged atoms of thorium and uranium react with oxygen, increasing their molecular weight and allowing them to sepa- rate from other overlapping signals that can disguise their presence. Among other uses, the innovation may allow chemists to further hone the chemistry that produces the world’s purest electroformed copper. The copper forms a key component of sensitive physics detectors, including those used for in- ternational nuclear treaty verification. pnnl.gov.
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