A research collaboration led by Livermore scientist Magnus Lipp and former Laboratory scientist Joseph Bradley has answered a long-standing question in condensed-matter physics regarding the large isostructural volume collapse that cerium undergoes at high pressure. Scientists have been debating about the fascinating behavior of this rare-earth element since the 1970s. The team, which included colleagues from the University of Washington, Stanford University, SLAC National Accelerator Laboratory, and Carnegie Institute of Washington, found an experimental signature that strongly favors one of the proposed models, called the Kondo Volume Collapse. Understanding this unusual behavior is important because cerium can be used as a catalyst and a fuel additive.
As part of this study, the researchers developed a methodology that uses x-ray spectroscopy to study rare-earth systems at high pressure and directly probe quantum mechanical observables, which makes the methodology a powerful test of theory. The collaborators also built instrumentation that speeds up data collection by a factor of 100 or more. Results from the study appeared in the November 9, 2012, edition of Physical Review Letters.
“As a result of this work, we can not only answer the cerium question,” says Bradley, “but we can also study many systems and gain some real understanding about f-electron delocalization in general, which is a ‘holy-grail’ question in condensed-matter physics and one that can be directly transferred to the 5f electron in actinides.”Contact: Magnus Lipp (925) 424-6662 (firstname.lastname@example.org).
A new understanding of planetary evolution could emerge from experiments on magnesium oxide under high pressures and temperatures. Scientists from Lawrence Livermore and the University of California at Berkeley, working at the University of Rochester’s Laboratory for Laser Energetics and at Livermore’s Jupiter Laser Facility, subjected magnesium oxide to pressures from about 0.3 to 1.4 trillion pascals (3 to 14 million times Earth’s atmospheric pressure) and temperatures reaching up to 50,000 kelvins—conditions found at the center of Earth and in giant “super-Earth” planets in other solar systems. The molecular bonding of the mineral samples changed substantially in response to these extreme conditions, including transformation to a new high-pressure solid phase not previously observed. In fact, the team’s results indicate that when magnesium oxide melts, it changes from an electrically insulating material such as quartz to an electrically conductive metal similar to iron.
Drawing from these findings and other recent observations, the team concluded that although magnesium oxide is solid and nonconductive on present-day Earth, early Earth’s magma ocean might have been able to generate a magnetic field. Likewise, the metallic, liquid phase of magnesium oxide can exist today in the deep mantles of super-Earth planets, as can the newly observed solid phase.
“Our findings blur the line between traditional definitions of mantle and core material and provide a path for understanding how young or hot planets can generate and sustain magnetic fields,” says Stewart McWilliams, who led the project as part of the research for his Ph.D. thesis. Livermore scientists Jon Eggert, Peter Celliers, Damien Hicks, Ray Smith, and Rip Collins also contributed to this study, which was published in the December 7, 2012, issue of Science.Contact: Jon Eggert (925) 422-3249 (email@example.com).
In a series of free-electron laser experiments on highly charged iron, an international collaboration involving Livermore researchers has identified a new solution to an astrophysical phenomenon, which will help scientists understand why observations from orbiting x-ray telescopes do not match theoretical predictions. This study was conducted with the Linac Coherent Light Source at SLAC National Accelerator Laboratory. The team’s results appeared in the December 13, 2012, edition of Nature.
Highly charged iron produces some of the brightest x-ray emission lines from hot astrophysical objects, such as galaxy clusters, stellar coronae, and the Sun. However, its spectrum does not fit into even the best astrophysical models. The intensity of the strongest iron line is generally weaker than predicted. Scientists have questioned whether this discrepancy is caused by incomplete modeling of the plasma environment or by shortcomings in how models treat the underlying atomic physics.
“Our measurements suggest that the poor agreement is rooted in the quality of the underlying atomic-wave functions rather than in insufficient modeling of collision processes,” says Livermore physicist Peter Beiersdorfer, who helped initiate the project. This study paves the way for future astrophysics research using free-electron lasers such as LCLS, which for the first time allows scientists to measure atomic processes in extreme plasmas in a fully controlled way.Contact: Peter Beiersdorfer (925) 423-3985 (firstname.lastname@example.org).