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Previous efforts to produce a comprehensive tabulation of atomic x-ray transition energies have been hampered by the fact that a) detectors having a broad spectral range of x-ray energies have had poor resolution, and b) detectors capable of high energy resolution could not cover a broad spectral range. Previous compilations of x-ray transition energies have been the result of many measurements using different instruments and procedures. No single scheme has existed to tie these measurements together. The NIST microcalorimeter x-ray detector using a transition-edge sensor (TES) is capable of high resolution measurements of x-ray transition energies over a broad spectral range. It is now possible to measure in a single spectrum a large number of x-ray lines, either from multiple elements or from different series in the same element. We have demonstrated both of these capabilities.
Intended impact: The most up-to-date tabulation of x-ray transition energies (used for x-ray work world-wide) is the result of a long-term NIST program directed by Richard Deslattes whose most recent results were published in 2003. Despite the fact that the values were upgraded from previous tables by 35 years of additional results, a large number of x-ray transition lines are based on either extrapolations of a relatively small number of actual line measurements or on theoretical calculations. X-ray transition energies given in certain regions of the periodic table are known to be inconsistent. There is an opportunity here to make actual measurements which are experimentally self-consistent.
Objective: We chose to measure x-ray transition energies from NIST standard reference glasses that contained several elements at the same time. Various atomic transitions of each of the elements could be excited using the energetic beam of an electron microscope. This resulted in the production of x-ray emission from a number of atomic transitions that could be observed in a single spectrum of the microcalorimeter. A calibration of the microcalorimeter using the previously published values of the x-ray transitions would yield not only an energy scale for the spectrum, but would test the accuracy of the published values as well.
Goals: To test the consistency of the universal energy scale of previously published atomic x-ray transitions, looking at both different transition series (differing widely in energy) from the same elements, and energies from the same atomic transition series of different elements. These previous values are mostly the result of x-ray diffraction measurements so that a comparison of x-ray lines of widely different transition energies could not be validated.
Technical approach: The thermal response of the microcalorimeter detector is ideally suited to creating a highly linear response to the energy of absorbed individual x-ray photons. Using a few highly-measured x-ray transition lines, it is possible to calibrate the energies of all the other measured transitions to within the spectral range of a given microcalorimeter head. We found that it was necessary to add only a small nonlinear correction to the energy scale from 400 eV to 8000 eV. All lines are therefore referenced to an energy scale determined by a few "standard" lines.
Start Date:January 3, 2005
Lead Organizational Unit:mml
NIST TES microcalorimeter, electron beam probe, NIST microcircuit fabrication facilities (Boulder)
Terrence Jach (CSTL, Gaithersburg)
Joel Ullom (EEEL, Boulder)
Related Programs and Projects:
Quantitative analysis of elemental concentrations using the microcalorimeter and electron probe, microcalorimeter programs for other purposes developed at NIST Boulder, electron beam ion trap atomic emission spectroscopy of highly-ionized elements using a semiconductor microcalorimeter ( Div. 842, John Gillaspy)
"The Microcalorimeter X-ray Detector: A True Paradigm Shift in X-ray Spectroscopy," Terrence Jach, Joel Ullom, and Tim Elam, Proceedings of the 21st International Conference on X-ray and Inner-shell Processes, The European Physics Journal—Special Topics, accepted for publication.