10 July 2008
Research into the understanding of how X-rays interact with matter could lead to the production of more powerful exotic magnets, such as those that will make electric vehicles more efficient and cost effective or those required to develop a new generation of CT scanners. By rekindling an effect first discovered 70 years ago to understand the processes that cause X-rays to be absorbed by matter, a team of scientists led by the University of Warwick, working alongside colleagues at the STFC Daresbury Laboratory in Warrington and the Diamond Light Source in Oxfordshire, have uncovered subtle details about electrons that determine properties such as chemical bonding and the formation of magnetism. The full paper on this research has been published (10 July) in the scientific journal, Nature.
As is well known, X-rays have the ability to pass through solid objects, but in the process the X-rays always experience some loss or absorption. This is why medical X-rays show features from inside a patient’s body – the X-rays experience increased absorption in more dense material such as bone and these areas show up as shadows on the X-ray image. The absorption of an X-ray occurs when the X-ray interacts and transfers its energy to an electron or an atom, so measuring the absorption of X-rays can tell us a lot about the state of these electrons and atoms.
In 1941 a remarkable effect was observed by Gerhard Borrmann, known as the ‘Borrmann effect’. Borrmann noticed that X-rays passing through a crystal of germanium could experience much reduced absorption. This team of scientists realised that in the Borrmann effect it is only the dominant absorption, known as dipole absorption that is reduced. This allows a weak contribution to the absorption known as quadrupole absorption, to be measured. In most measurements, this smaller absorption is extremely difficult to distinguish from the stronger dipole absorption. Using X-rays at the STFC Daresbury Laboratory, they have been able to utilise this effect to measure the illusive quadrupole absorption component.
Determining quadrupole absorption is the answer to understanding many important material properties. Measurement of this absorption provides information about how the electrons are distributed in the area around atoms, known as orbitals, focusing on the orbitals which are responsible for magnetism and chemical bonding. Understanding these orbitals could be the key to understanding and developing new exotic magnets which can operate in extreme conditions and temperatures, such as those required to operate electric vehicles, advanced superconductors, or new X-ray imaging techniques.
It is amazing that the Borrmann effect, discovered nearly 70 years ago, should prove to be the solution to gaining insight into the formation of magnetism – a problem that is at the forefront of 21st century science
Dr David Laundy, research scientist at STFC Daresbury Laboratory
Prof Steve Collins, Principal Beamline Scientist at Diamond, adds "Here at Diamond we will be able to build on the successes that the Daresbury Laboratory has facilitated in this area of research and advance these studies over the coming years."
This research paper has been published as an advance online publication at http://www.nature.com/nnano/index.htm.
Quadrupole transitions revealed by Borrmann spectroscopy’ Robert F. Pettifer, Stephen P. Collins & David
Paper reference: doi: 10.1038/nature07099
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