Each of us is the scene of billions of collisions, every microsecond of our lives. Indeed, our world and the universe around it thrive on the colliding of minute particles – fundamental processes that cause it to function as it does.
"Atomic collisions are the interactions between atoms, electrons, positrons, photons, and ions. They go on all around and inside us, all the time. They are at the root of all chemical processes, which form everything from stars to microbes, gigantic gas clouds to ourselves," says Professor Igor Bray of Curtin University. "To understand them is to gain an insight into what makes our universe tick."
Collision science also holds the key to a host of extremely useful applications from 'green' lighting and better TV screens, to novel industrial materials, new energy sources and improved cancer diagnosis.
Professor Bray's team is using Australia's most potent scientific instrument, the National Computational Infrastructure's supercomputer, Vayu, to probe the heart of collision science, exploiting a world-first mathematical breakthrough which has taken them almost ten years to perfect.
"We use Vayu to calculate interactions between particles on the atomic scale. These include electron, positron, or photon interactions with atoms. To take a typical example, you'd think that the way a single electron reacted with a hydrogen atom, consisting of a proton and an electron, would be fairly straightforward. It isn't. It is unbelievably complex. It takes very, very large computer power to explore all the possible interactions," he says.
Indeed this so-called 'Coulomb three body problem' was so complex it remained unsolved for 80 years following the discovery of quantum mechanics in the 1920s, until Prof. Bray and his colleagues hammered out the essential mathematics to describe it: "We cracked it in a rather interesting way, computationally and without knowing quite how we had got it right. But we were then able to work backwards from the solution to define the whole process. That would never have been possible without some very high-end supercomputing being available here in Australia."
The Convergent Close Coupling theory they have developed provides a unified approach to quantum collision theory for science worldwide. It has been extended to incorporate photons, positrons, protons and antiprotons and is now applied generally across atomic, molecular and high energy physics. It enables scientists to produce accurate models of particle systems and collisions, and in many cases to calculate their outcomes far more accurately than is possible with an experiment.
The goal of their present work is to further develop the theory and to calculate atomic collision processes of particular interest to science and industry.
"All light that we see is either due to, or is influenced by, collisions at the atomic scale. All chemical reactions are examples of atomic collisions. Consequently, there is no shortage of useful applications in this field," Prof. Bray says. "This work is of practical benefit in diverse scientific fields and industries, providing a fundamental basis for advances in astrophysics, plasma displays, lasers, fusion energy, domestic lighting, medical and materials applications."
For example the ARC Centre of Excellence for Antimatter-Matter Studies is using the technique to enhance the performance of medical PET scanners, which employ a positron-electron collision as a means of detecting cancers. "At the moment the images they produce of cancers in soft tissues are rather fuzzy, but by better understanding how positrons react with the water in our bodies, we can sharpen those images, enabling the doctors to target the cancer with far greater precision and destroy it without harming healthy tissue," Professor Bray says.
To solve a practical problem such as defining a cancer, building a better light bulb or plasma screen, or creating a future nuclear fusion reactor for clean electricity generation depends primarily on having a firm grasp of the fundamental science which underlies the issue, he adds.
"There is also no limit on the complexity of the problems of interest, particularly those involving molecular participants," says Prof. Bray. "However the complexity of what we can undertake is critically determined by the computational power available to us. Having access to one of the world's most powerful computers is essential, or Australia cannot perform world-class science in this field. Industry around the world is starting to make major use of this branch of science – so NCI is, quite simply, critical infrastructure."
