Washington, April 19 : Scientists have used high-energy X-rays to discover and study the structure of plutonium nanoclusters, which contaminate groundwater, thus increasing the risk of sickness in humans and animals.
The finding was made by scientists at the US Department of Energy's Argonne National Laboratory, in collaboration with researchers from the University of Notre Dame, using the Argonne Advanced Photon Source (APS).
"When plutonium forms into the clusters, its chemistry is completely different and no one has really been able to assess what it is, how to model it or how to separate it," said Argonne senior chemist Lynda Soderholm.
"People have known about and tried to understand the nanoclusters, but it was the modern analytical techniques and the APS that allowed us understand what it is," she added.
The analysis revealed that the nanoclusters are made up of exactly 38 plutonium atoms and had almost no charge.
Unlike stray plutonium ions, which carry a positive charge, they are not attracted to the electrons in plant life, minerals, etc. which stopped the ions' progression in the ground water.
Till now, models have been based on the free-plutonium model, creating discrepancies between what is expected and reality.
According to Soderholm, with knowledge of the structure, scientists can now create better models to account for not only free-roaming plutonium ions, but also the nanoclusters.
The clusters also are a problem for plutonium remediation. The free ions are relatively easy to separate out from groundwater, but the clusters are difficult to remove.
"As we learn more, we will be able to model the nanoclusters and figure out how to break them apart," said Soderholm. "Once they are formed, they are very hard to get rid of," she added.
Other experiments have shown some clusters with different numbers of plutonium atoms and the research team plans to examine them.