Ion track mystery cracked

A research team from The Australian National University (ANU) has cracked the mystery surrounding the tracks that heavy ions make as they pass through solids — and the findings could potentially have a wide impact for nanotechnology research, geological dating and interplanetary science.

The team, led by ARC Australian Research Fellow Dr Patrick Kluth from the ANU Research School of Physical Sciences and Engineering, has discovered that the ion tracks left by heavy ions as they move across a solid are consistent with a frozen-in, nanoscale acoustic shock wave.

The researchers made the discovery by measuring and simulating the structure of an ion track in glass. The findings indicate that the shock wave is generated by the sudden thermal expansion at the ion track centre as the ion passes through the solid.

“The finding is a milestone in understanding the interactions of highly energetic ions with solids and has ramifications for materials science, nuclear physics, geochronology, archaeology and interplanetary science,” said Kluth.

“Our methodologies can be readily applied to other materials and can be expected to produce a significant body of experimental results on the structure of ion tracks that has been inaccessible for the last five decades.”

Kluth said that the finding could revolutionise geological dating.

“Ion tracks in silicates are used for geological dating purposes, but the dating measurements used at the moment employ chemical etching, which destroys the structure in the fission tracks in order to make them visible.

"This structure can carry important additional information such as thermal history and external pressure during track formation and with the measurement protocols used for our work we have direct access to such properties that are inaccessible with other techniques," he said.

“The findings also have significant potential impact for interplanetary science. In space, equipment is exposed to very high energy cosmic radiation and the response of materials to that is important in designing reliable electric components."

The discovery could also play an important role in improving nuclear waste management and materials science, which uses ion tracks as templates for the growth of nano-wires.

The findings are published in October's Physical Review Letters.