by Jacob Aron
Devoted fans can wait hours on the red carpet to get their favourite movie star’s autograph, but that’s nothing compared to acquiring the signature of plutonium-239. After 50 years of trying, physicists have finally managed to analyse the fissile isotope using nuclear magnetic resonance (NMR) spectroscopy. This could potentially allow them to develop improved methods for storing waste from nuclear power plants.
NMR spectroscopy is used to determine the molecular structure of many materials, particularly those in which the nucleus has a quantum spin of one half, which includes common hydrogen and carbon isotopes. Plutonium-239 is the last nucleus with such a quantum spin left to analyse – partly because plutonium has a number of complex magnetic properties that interfere with the measurements. Another reason is that there are restrictions involved in handling potentially dangerous nuclear material.
To overcome the magnetic property problems, Georgios Koutroulakis of the Los Alamos National Laboratory in New Mexico and colleagues cooled very pure plutonium dioxide powder to just 4 °C above absolute zero. This widened the window of time in which they could perform measurements and nearly eliminated the interfering magnetic effects.
Nuclear waste potential
Koutroulakis says choosing this form of plutonium was key to their success, as others in the field had previously dismissed it or did not have access to samples of sufficient quality. He also puts his team’s success down to their perseverance and a touch of luck. “Actually, we detected the signal when we were about to give up,” he says.
Having determined the isotope’s signature, physicists should now be able to identify how plutonium fits into the structure of compounds and molecules, allowing them to better analyse the chemical properties of nuclear fuels and waste.
“One could potentially take a small sample of nuclear waste and – in a safe, easy and relatively cheap way – determine very accurately what’s in there to take the appropriate actions for its storage and subsequent use,” explains Koutroulakis.
“We can use this to interrogate nuclear materials that contain plutonium,” agrees Ian Farnan, who investigates nuclear waste disposal at the University of Cambridge and was not involved in the research. His team has a more advanced NMR machine and will now attempt to replicate the results at room temperature, making them more useful for real-world applications. “I’m quite looking forward to testing that out,” he says.