Lawrence Livermore National Laboratory



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Deflecting Asteroids with Neutron Energy

Lawrence Livermore National Laboratory and the Air Force Institute of Technology (AFIT) partnered to identify the best neutron energies for deflecting an asteroid. In research featured in the June 2021, issue of Acta Astronautica, the scientists compared the resulting asteroid deflection from two neutron energy sources, representative of fission and fusion neutrons, allowing for side-by-side comparisons and for the effect of the neutron energy on the resulting deflection to be quantified.

The two-phase study reviewed neutron energy deposition and asteroid deflective response. For the energy deposition phase, Los Alamos National Laboratory’s Monte Carlo N-Particle radiation-transport code simulated a standoff detonation of neutrons, analyzing the thousands of cells within the asteroid and tracking each cell to generate energy deposition profiles or spatial distributions of energy throughout the asteroid. In the deflection phase, Livermore’s 2D and 3D Arbitrary Lagrangian-Eulerian hydrodynamics code simulated the asteroid’s response to the energy depositions. The results indicated which portions of the asteroid would remain solid and which would vaporize, causing blow-off debris and ultimately changing the asteroid’s speed and direction. These findings provide insight into the ideal neutron energy spectrum needed for the necessary velocity change or deflection.

Research team members agree that two options exist for defeating an asteroid: disruption (imparting so much energy to the asteroid that it shatters into fragments moving at extreme speeds) or deflection. Livermore physicist and study co-author Joseph Wasem notes, “Deflection would be safer than disruption as long as sufficient warning time exists to launch a deflection response.”
Contact: Joseph Wasem (925) 423-9232 (wasem2@llnl.gov).


Photocathode Enhances Hydrogen Production

As plants create energy from photosynthesis, a photocathode utilizes light and water for efficient hydrogen production. Lawrence Livermore and Lawrence Berkeley national laboratories collaborated with the University of Michigan following the university’s discovery that silicon and gallium nitride (Si/GaN) photocathodes are capable of harnessing sunlight and water into carbon-free hydrogen. Their work, released in the April 5, 2021, issue of Nature Materials, found that a chemical reaction can transform gallium nitride into gallium oxynitride, resulting in self-improving capabilities of a Si/GaN photocathode—findings that could accelerate the production of hydrogen fuel cells.

University of Michigan professor Zetian Mi initiated the discovery when his Si/GaN photocathode achieved a record-breaking 3 percent solar-to-hydrogen efficiency. With Berkeley scientists, Mi conducted microscopy and spectroscopy experiments, revealing a 1-nanometer layer of gallium oxynitride had formed along the sidewall of the GaN grain, adding hydrogen evolution reaction sites. Livermore’s Anh Pham and Tadashi Ogitsu performed density functional theory simulations, confirming the observations.

The self-improving ability of Si/GaN photocathodes marks a leap forward for solar-fuel production. Not only is the unusual property in Si/GaN more efficient and stable than semiconductor materials studied in the past, the technology is also relatively inexpensive. Livermore co-author Ogitsu says, “We hope our findings and approach will be used to further improve renewable hydrogen production technologies.”
Contact: Tadashi Ogitsu (925) 422-8511 (ogitsu1@llnl.gov).


Pandemic Lowers U.S. Energy Consumption

An energy flow chart released by Lawrence Livermore National Laboratory shows that Americans used less energy in 2020—a change due, in part, to the COVID-19 pandemic. Shelter-in-place orders were the leading factor in the 14 percent decline in transportation and the 11 percent drop in commercial energy use. Continued deployment of renewables resulted in a 19 percent increase in solar energy and a 10 percent boost in wind energy, both of which can replace coal as a source of power.

“Solar and wind continue to show year-on-year growth, which is an impressive change for the energy system,” says A.J. Simon, Livermore energy systems analyst. Although many more Americans worked from home in 2020, residential energy consumption rose only 2 percent due to a mild winter and higher efficiency homes. Energy consumption is measured in British Thermal Units (BTUs). One kilowatt-hour—comparable to the energy required to operate an LED lightbulb for one week—is equivalent to 3,412 BTUs. Overall, Americans used 92.9 quads (quadrillion BTUs) of energy in 2020, which is 7.2 quads or 7 percent less than energy consumption in 2019. The efficiency of the nation’s cars, lightbulbs, and factories contribute to how much energy is rejected and how much fuel and electricity is being used productively. These numbers show positive changes in the way the country uses energy, and that less energy is being lost or rejected during use.
Contact: Hannah Goldstein (925) 422-9614 (goldstein12@llnl.gov).