A multiinstitution collaboration is developing a neutron imaging system for the Sandia Z facility. The initial system design is for slit aperture imaging system capable of obtaining a one-dimensional image of a 2.45 MeV source producing 5x10(12) neutrons with a resolution of 320 microm along the axial dimension of the plasma, but the design being developed can be modified for two-dimensional imaging and imaging of DT neutrons with other resolutions. This system will allow us to understand the spatial production of neutrons in the plasmas produced at the Z facility.
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http://dx.doi.org/10.1063/1.2988819 | DOI Listing |
J Am Chem Soc
December 2024
School of Chemistry, University of New South Wales, Kensington, NSW 2052, Australia.
Hydrofluoroolefins (HFOs) and hydrochlorofluoroolefins (HCFOs) are the leading synthetic replacements for compounds successively banned by the Montreal Protocol and amendments. HFOs and HCFOs readily decompose in the atmosphere to form fluorinated carbonyls, including CFCHO in yields of up to 100%, which are then photolyzed. A long-standing issue, critical for the transition to safe industrial gases, is whether atmospheric decomposition of CFCHO yields any quantity of CHF (HFC-23), which is one of the most environmentally hazardous greenhouse gases.
View Article and Find Full Text PDFJ Phys Chem Lett
December 2024
Combustion Research Facility, Sandia National Laboratories, Livermore, California 94550, United States.
We demonstrate the capability of a narrow linewidth quantum cascade laser (QCL) to selectively excite a very narrow velocity range of nitric oxide (σ ≤ 7(3) m/s) with a pure ro-vibrational quantum state. By implementing a counter-propagating geometry, the molecules are selectively excited according to the Doppler shift of the ro-vibrational transition frequency such that the velocity width associated with the excited molecules depends only on the QCL linewidth. We demonstrate a velocity distribution limited by the effective linewidth of our free-running QCL (Γ = 3.
View Article and Find Full Text PDFACS Phys Chem Au
November 2024
Combustion Research Facility, Sandia National Laboratories, Livermore, California 94550, United States.
Herein, we report on the ultrafast photodissociation of nickel tetracarbonyl-a prototypical metal-ligand model system-at 197 nm. Using mid-infrared transient absorption spectroscopy to probe the bound C≡O stretching modes, we find evidence for the picosecond time scale production of highly vibronically excited nickel dicarbonyl and nickel monocarbonyl, in marked contrast with a prior investigation at 193 nm. Further spectral evolution with a 50 ps time constant suggests an additional dissociation step; the absence of any corresponding growth in signal strongly indicates the production of bare Ni, a heretofore unreported product from single-photon excitation of nickel tetracarbonyl.
View Article and Find Full Text PDFJ Phys Chem A
December 2024
Combustion Research Facility, Sandia National Laboratories, Livermore, California 94550, United States.
Nat Commun
October 2024
Energy Technologies Area, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
Identifying transition states-saddle points on the potential energy surface connecting reactant and product minima-is central to predicting kinetic barriers and understanding chemical reaction mechanisms. In this work, we train a fully differentiable equivariant neural network potential, NewtonNet, on thousands of organic reactions and derive the analytical Hessians. By reducing the computational cost by several orders of magnitude relative to the density functional theory (DFT) ab initio source, we can afford to use the learned Hessians at every step for the saddle point optimizations.
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