Explosive super sensing
A FEW YEARS ago there was a worldwide hike in food prices because the United States made incentives for making biofuels—gasoline with ethanol, an environmentally friendly alternative to regular gas—attractive. The need for biofuels is clear, but how do we tell if manufacturers are actually making fuel from crops and not just repackaging normal gas and charging double?
Seemingly unrelated, Vancouver sits directly over a relatively quiet fault line—a place where the pieces that make up the Earth’s surface meet. How quiet the fault line actually is, however, is difficult to determine without a history of its past activity.
There is also a need to monitor our nuclear waste, making sure that none of it is being spread from secure storage.
The solution to all these problems lays within tiny quantities of telltale radioactive isotopes that give the necessary history. How can the history of a few atoms within an isotope be detected to solve all of the above and similar problems?
Liam Kieser is an associate professor of physics at the University of Ottawa and the director of the IsoTrace Laboratory in Toronto. He works on using accelerator mass spectrometry (AMS) to reach unparalleled levels of sensitivity, finding the smallest traces of isotopes that would be undetectable normally.
AMS uses a particle accelerator to bombard a sample with fast-moving particles, freeing and ionizing them. Imagine billiard balls hit with a wrecking ball. The atoms in the sample shoot out, guided by electric and magnetic fields. Different masses move differently in the field and researchers can pick out the particles of interest by their mass.
Thanks to the high energy projected from the mass spectrometer, molecules that might have the same mass as the isotope in question explode into fragments, which no longer have the same mass. On the other hand, the isotopes come out with so much energy that techniques from particle physics can be used to detect them down to the single atom level. Altogether, AMS can detect the presence of an isotope down to a millionth of a billionth of a gram.
Kieser works on ways of further increasing the sensitivity of AMS, devising methods of separating not just isotopes from molecules of the same mass, but isotopes from other atoms with the same mass. While molecules can be split easily, the other atoms are effectively indestructible.
Recently he’s developed a method for separating Sulphur 36 from the radioisotope Chlorine 36. Chlorine 36 is of great interest in ground water studies, since a great deal was generated during nuclear testing in the 1950s. Upon completion of the Centre for Advanced Photonics and Environmental Analysis at U of O, Canada’s only accelerated mass spectrometer will move to Ottawa in a new state of the art lab, providing the tools for extreme sensing.