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Thomas Cocolios, measuring an atom with humane results
© CERN
Depth interview

Thomas Cocolios, measuring an atom with humane results

Researching the smallest particles in the universe requires the largest equipment and the broadest international coalitions.

5 minutes
19 July 2021

No one could be better situated to meet this challenge than Professor Thomas Cocolios of the division of Nuclear and Radiation Physics.

Born in the United States to a Greek father and French mother, Professor Thomas Cocolios is who you would design if you sought to create the perfect international researcher. He attended McGill University in Montreal, worked at nuclear facilities in the United States and Canada, obtained his PhD at KU Leuven, and continued his research at CERN in Switzerland. His background allows him to break through the many barriers intrinsic to the study of high-level nuclear physics, be they linguistic, diplomatic, or the most significant barrier in science: understanding.

The problem is that nuclear physics is dauntingly complex. When talking about nuclear physics to a layperson, it’s almost required to speak in a riot of analogies, as Professor Cocolios does with gusto.

Professor Cocolios on exploring an atomic nucleus: “We actually use the electron … it would be like trying to understand the surface of the earth by looking at the GPS signal from the cell phone of people working around the earth, right? You would get a bit of an idea of the topography.”

Or stabilising a particle beam to improve the accuracy of his measurements: “We accelerate the beam … picture yourself on a bike, you try to be perfectly balanced, but if you’re at rest you’re always going to be leaning to one side or the other until you fall. However, if you’re accelerated you’re not falling to the side anymore because you’re going forward so fast that the little wobbliness is taken along with it. And that’s what we do with the atoms, we accelerate them so that their wobbliness, which limits our resolution, gets erased.”

There are many more analogies in his repertoire. You could say his discourse orbits the technical details like an electron orbiting an atomic nucleus.

Yet when the situation requires, Professor Cocolios will happily speak directly about nuclear physics. He does so frequently, whether with high schoolers touring a particle accelerator, or with his most demanding peers at conferences. No matter how intricate the technical or conceptual details, he makes it possible to appreciate the implications of his work for scientific understanding on a number of fronts.

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Laser measurement

At its heart, Thomas Cocolios’ research is simple: he explores the shape of atomic nuclei. The cluster of protons and neutrons stuck together at the core of a copper or polonium atom is not usually a sphere, as one might expect. Most often, it’s an elongated sphere, like an egg or a rugby ball. Next most prevalent is a squashed sphere, like the earth itself, which bulges outward slightly along the equator (Professor Cocolios’ analogy). A sphere is only the third most likely shape.

Professor Cocolios explores the shape of the nucleus to learn about the origin of the elements, because what we know about exotic atomic particles right now is surprisingly limited. Lighter elements are fused in the cores of stars, whilst heavier elements are formed in the collisions amongst neutron stars and black holes; we simply cannot easily replicate those high-energy events on earth. The truth is that we don’t even fully understand the properties of many of the isotopes that we can produce in our nuclear reactors, despite having created them as fission by-products for the past ninety years.

So Professor Cocolios seeks information on atomic nuclei to fill in the gaps in our knowledge. He does this by using lasers to measure the changing colour of an atom. The electrons that surround the nucleus give an atom its colour, and the orbital occupied by an electron will change based on the shape of the nucleus. Professor Cocolios can measure this colour change to an accuracy of more than one part in a million, and determining new methods to attain that level of accuracy has been the main thrust of his research throughout his career. With revised knowledge from these new experimental methods in hand, we can test and refine existing nuclear models.

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Isotope factories

Yet there are more concrete benefits to his research than just filling in the gaps in our knowledge. The processes Professor Cocolios uses to obtain his test materials are the same as those that result in radioactive particles for medical purposes. “We shoot a particle – a proton typically – onto a target, say uranium, as you heat it up to a high temperature … and a lot of different radioactive nuclei that would be in the target come out. On their way out you make them go through what we call an ion source which transforms them from atoms to ions – charged particles – , and then we can apply electric and magnetic fields to them to accelerate them, manipulate them, and bring them wherever we want them to be … for you to shine a laser on, or for you to collect and make a radiopharmaceutical product to inject into a patient, it doesn’t matter, the technology is the same for both. We call some of those facilities radioactive isotope factories.”

In creating these medical-grade isotopes, Professor Cocolios has also had success collaborating with UZ Leuven to further their efforts in nuclear medicine and molecular imaging. Further collaboration with the materials engineering department at KU Leuven has also yielded tangible results. “We’re shining protons onto the starting materials, and it might sound trivial, but the sort of conditions under which we operate are so extreme that you need materials that can sustain that, and Leuven is actually at the forefront of that technology. By collaborating, we’ve actually already developed a series of materials that nobody had ever thought of before.”

Professor Cocolios encourages this pairing of fundamental research and practical results, but wouldn’t want to sacrifice one for the other: “Without fundamental research there is no innovation. I’m very proud of what I’m doing innovation-wise … and if you do not have the basic fundamental research to drive the developments, your innovation will dry out.”

Fortunately, Professor Cocolios is well-placed to continue this collaboration in the future, with innovation (and analogies) spinning out of KU Leuven for years to come.

(gp)

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