Earth and Planetary Science
EPS Geophysics

Pandemic does not prevent new PhD student from succeeding

Tuesday, November 24, 2020

Within five months of joining our PhD program, Rustin Domingos, succeeded in having his first research article entitled "Simulations and Experiments Reveal Effect of Nanopores on Helium Diffusion in Quartz" accepted for publication in the journal of Earth and Space Chemistry. This joint theoretical-experimental project was sparked by a drastic disagreement between laboratory data and results from computer simulations for the diffusion of helium atoms in quartz crystals.

This is important because the diffusion of noble gases in minerals is often utilized to reconstruct the thermal histories of rocks.  Computer simulations of helium in perfect quartz crystals predicted that already at room temperature, all helium atoms would diffuse out of the crystal because the helium atoms encounter very lower energy barriers along the crystal's z channel. Taken at face value, this would imply all helium would have diffused out of the crystal before the experiments even began. Conversely, however, the lab measurements showed that temperatures between 70 and 220 degrees Celsius were required for most helium atoms diffuse out of quartz crystals. "http://militzer.berkeley.edu/papers/Domingos_Tremlay_Shuster_Militzer_2020.pdf"

In the article, this discrepancy is resolved by introducing the novel hypothesis that helium atoms reside inside nanopores in the quartz crystal. The calculations showed that activation energy for helium atoms to diffuse from the nanopore into the crystal matched experimental data. A consistent effective diffusion model was constructed and the nanopore concentration was estimated to be approximately . The lab measurements were conducted in Prof. Shuster's lab by former EPS graduate Marissa Tremblay (now assistant professor at Purdue University). Prof. Militzer supervised the computer simulations and modeling effort.