Gregory Brown (16-ERD-020)
This project will provide high-accuracy atomic-parameter measurements of highly charged ions. The data will be used to benchmark models being used to study extrasolar and terrestrial sources and to test models of fundamental atomic physics parameters, such as transition energies and excitation cross sections of multi-electron ions of iron-group elements, used by the astrophysics and nuclear security communities.
One of the most rapidly advancing fields of astrophysics is x-ray astronomy. The last decade has seen profound growth in discoveries resulting from the successful operation of orbiting x-ray observatories including the Chandra X-Ray Observatory, XMM-Newton (X-Ray Multi-Mirror Mission), and NuSTAR (Nuclear Spectroscopic Telescope Array). The Japanese Aerospace Exploration Agency's ASTRO-H, also known as Hitomi, orbiting observatory will help decipher the x-ray emission from sources observed by NuSTAR and will extend high-resolution spectroscopy beyond the limits of Chandra and XMM-Newton. At the center of Hitomi's instrument suite is the soft x-ray spectrometer, which will provide the first-ever high-resolution, high signal-to-noise spectra of some of the most exotic, most energetic sources in the universe, including black holes, neutron stars, active galactic nuclei, high-mass x-ray binaries, and supernova remnants. Decoding the high-resolution spectra requires accurate, complete sets of atomic data, most of which are generated using highly sophisticated atomic calculations. Unfortunately, most of the calculated data has not been tested experimentally in a systematic way. The lack of complete, systematic experimental benchmark measurements in the case of multi-electron ions limits and often precludes accurate interpretation of high-resolution spectra. We intend to use Livermore Laboratory's EBIT-I electron-beam ion trap to make anchor measurements of the x-ray emission from multi-electron ions of iron-group elements (elements from chromium to nickel in the periodic table). These data will be used to decode the x-ray emissions from exotic extra-solar sources measured with instruments on orbiting x-ray observatories.
Accurate, complete sets of atomic data are required to fully utilize the high-quality, high-resolution spectra of the soft x-ray spectrometer. The new physics accessible by the soft x-ray spectrometer will make it possible to reveal the large-scale structure of the universe by observing clusters of galaxies. Additionally, the soft x-ray spectrometer will be able to detect the ejecta patterns and presence of rare elements such as chromium, manganese, and nickel in supernova remnants, providing constraints on its explosion mechanism. We expect to aid this effort by providing high-accuracy atomic-parameter measurements of highly charged ions, which are necessary to better understand high-resolution x-ray spectra measured from celestial sources, at Livermore’s EBIT-I facility. Its capability as an astrophysics facility provides a unique resource for assessing atomic data and addressing spectroscopic issues. The data gained from our work will be used to benchmark models being used to study extrasolar as well as terrestrial sources. The results will be used to test fundamental atomic physics parameters, such as transition energies and excitation cross sections, of multi-electron ions of iron-group elements found in Lawrence Livermore models, as well as those used by the astrophysics community.
The production of anchor measurements that can be used by the x-ray astrophysics community contributes to the Laboratory's space security mission research challenge. The benchmark data generated by this project will also be valuable in testing models being used to study the interiors of hohlraum target capsules and multi-electron high-atomic-number ions, enhancing the Laboratory's core competency in nuclear weapons science and supporting DOE's goal in nuclear security to strengthen key science, technology, and engineering capabilities and modernize the national security infrastructure.
FY17 Accomplishments and Results
In FY17 we (1) completed the steady-state measurements of cross sections of K-shell (closest shell to the nucleus) transitions in highly charged iron ions; (2) began cross section measurements of K-shell transitions in highly charged manganese and cobalt ions; (3) analyzed Hitomi x-ray spectrum of the Perseus Cluster; (4) analyzed data from NuStar and from Livermore's EBIT facility and used it to help interpret the Perseus spectrum; (5) prepared requests for beam time at the PETRA III advanced synchrotron light source in Hamburg, Germany, so that fluorescence measurements can be made; and (6) participated in the European Space Agency's Athena (Advanced Telescope for High-Energy Astrophysics) spatially resolved x-ray spectroscopy science working group.
Publications and Presentations
Hell, N. 2017. “Benchmarking Transition Energies and Emission Strengths for X-ray Astrophysics with Measurements at the Livermore EBITs.” PhD thesis, Friedrich-Alexander-Universität Erlangen-Nürnberg. LLNL-TH-727717.
Hitomi Collaboration. 2017. “Hitomi Constraints on the 3.5 keV Line in the Perseus Cluster," Astrophys. J. Lett. 837 (1):L15. doi:org/10.3847/2041-8213/aa61fa. LLNL-JRNL-731764.
——— 2017. “Measurements of Resonant Scattering in the Perseus Cluster Core with Hitomi SXS," Publ. Astron. Soc. Jpn. (forthcoming). LLNL-JRNL-740200.
——— 2017. “Solar Abundance Ratios of the Iron-Peak Elements in the Perseus Cluster," Nature (forthcoming). LLNL-JRNL-740598.