The NIST Vacuum Double-Crystal Spectrometer (VDCS) has been modernized and is now capable of recording reference-free wavelength-dispersive spectra in the 2 keV to 12 keV x-ray energy range. The VDCS employs crystals in which the lattice spacings are traceable to the definition of the meter through x-ray optical interferometry with a relative uncertainty <10−8. VDCS wavelength determination relies upon precision angle difference measurements for which the encoders of the rotation stages have been calibrated using the circle closure method for accurate, absolute angle measurement. The new vacuum-compatible area detector allows quantification of the aberration functions contributing to the observed line shape and in situ alignment of the crystal optics. This latter procedure is augmented with the use of a thin lamella as the first crystal. With these new techniques, x-ray spectra are registered with the VDCS on an absolute energy scale with a relative uncertainty of 10−6.

We use an array of transition-edge sensors, cryogenic microcalorimeters with 4 eV energy resolution, to measure L x-ray emission-line profiles of four elements of the lanthanide series: praseodymium, neodymium, terbium, and holmium. The spectrometer also surveys numerous x-ray standards in order to establish an absolute-energy calibration traceable to the international system of units for the energy range 4 keV to 10 keV. The new results include emission line profiles for 97 lines, each expressed as a sum of one or more Voigt functions; improved absolute energy uncertainty on 71 of these lines relative to existing reference data; a median uncertainty on the peak energy of 0.24 eV, four to ten times better than the median of prior work; and six lines that lack any measured values in existing reference tables. The 97 lines comprise nearly all of the most intense L lines from these elements under broad-band x-ray excitation. The work improves on previous measurements made with a similar cryogenic spectrometer by the use of sensors with better linearity in the absorbed energy and a gold x-ray absorbing layer that has a Gaussian energy-response function. It also employs a novel sample holder that enables rapid switching between science targets and calibration targets with excellent gain balancing. Most of the results for peak energy values shown here should be considered as replacements for the currently tabulated standard reference values, while the line shapes given here represent a significant expansion of the scope of available reference data.

A Cauchois-type spectrometer utilizing the (203) lattice planes at an oblique angle of 11.53° to the normal to the surface of a quartz transmission crystal recorded the Kα and Kβ spectral lines of six elements from Fe to Ag in the 6-22 keV energy range from a laboratory x-ray source. After deconvolving the natural lifetime widths and the image plate detector broadening from the observed spectral linewidths, the intrinsic crystal resolving power was determined to be 4000 at the lower energies and decreasing to 1000 at the higher energies. Previously, a Si wafer crystal exhibited twice this resolving power when the (331) planes had been used in asymmetric geometry. The investigation of diffraction with this quartz crystal, with a very similar lattice spacing and therefore spectral coverage, was motivated by the larger integrated reflectivity of quartz due to its well-known quasimosaicity upon elastic bending. The measured spectral linewidths were in good agreement with the widths calculated by accounting for various broadening mechanisms, including source size, crystal thickness, crystal height, crystal rocking curve width, geometrical aberrations, and possible spectrometer configuration errors. This is the first, to the best of our knowledge, demonstration of high resolving power achieved by asymmetric diffraction over a wide energy range (6-22 keV) and with detailed comparisons with theoretical broadenings. Based on these results, Cauchois spectrometers employing asymmetric planes of perfect quartz and silicon crystals can be reliably designed and optimized for high-resolution spectroscopy in the >6  keV energy range.

We report recent advances in absolute x-ray wavelength metrology in the context of producing modern standard reference data. Primary x-ray wavelength standards are produced today using diffraction spectrometers using crystal optics arranged to be operated in dispersive and non-dispersive geometries, giving natural-line-width limited profiles with high resolution and accuracy. With current developments, measurement results can be made traceable to the Système internationale definition of the meter by using diffraction crystals that have absolute lattice-spacing provenance through x-ray-optical interferometry. Recent advances in goniometry, innovation of electronic x-ray area detectors, and new in situ alignment and measurement methods now permit robust measurement and quantification of previously-elusive systematic uncertainties. This capability supports infrastructures like the NIST Standard Reference Data programs and the International Initiative on X-ray Fundamental Parameters and their contributions to science and industry. Such data projects are further served by employing complementary wavelength-and energy-dispersive spectroscopic techniques. This combination can provide, among other things, new tabulations of less-intense x-ray lines that need to be identified in x-ray fluorescence investigation of uncharacterized analytes. After delineating the traceability chain for primary x-ray wavelength standards, and NIST efforts to produce standard reference data and materials in particular, this paper posits the new opportunities for x-ray reference data tabulation that modern methods now afford.

We present newly measured spectra of the X-ray emission of a molybdenum metal anode subject to electron bombardment, using a very high dispersion silicon double-crystal spectrometer. The measurement includes the dipole-allowed KL, KM, and KN emission lines, based on an energy scale traceable to the Système International (SI) definition of the meter with a systematic uncertainty below ΔE/E = 10-6. The data are presented as parametrized multi-Lorentzian fits to the results, and as supplementary data with the complete spectrum of each line group, corrected for instrumental effects. The MoKL3 (Kα1) line energy was in complete statistical agreement with published measurements, and it showed no asymmetry. Other lines showed varying discrepancies with the literature which lie outside the bounds of probable experimental errors.

The properties of hot, dense plasmas generated by the irradiation of GaAs targets by the Titan laser at Lawrence Livermore National Laboratory were determined by the analysis of high resolution K shell spectra in the 9 keV to 11 keV range. The laser parameters, such as relatively long pulse duration and large focal spot, were chosen to produce a steady-state plasma with minimal edge gradients, and the time-integrated spectra were compared to non-LTE steady state spectrum simulations using the FLYCHK and NOMAD codes. The bulk plasma streaming velocity was measured from the energy shifts of the Ga He-like transitions and Li-like dielectronic satellites. The electron density and the electron energy distribution, both the thermal and the hot non-thermal components, were determined from the spectral line ratios. After accounting for the spectral line broadening contributions, the plasma turbulent motion was measured from the residual line widths. The ionization balance was determined from the ratios of the He-like through F-like spectral features. The detailed comparison of the experimental Ga spectrum and the spectrum simulated by the FLYCHK code indicates two significant discrepancies, the transition energy of a Li-like dielectronic satellite (designated t) and the calculated intensity of a He-like line (x), that should lead to improvements in the kinetics codes used to simulate the X-ray spectra from highly-charged ions.

ASTM F792, Standard Practice for Evaluating the Imaging Performance of Security X-ray Systems, provides test objects and methods for measuring the imaging performance of cabinet X-ray systems used at security checkpoints. The standard is widely used, with many thousands of ASTM F792 test objects utilized throughout the world. The last major revision of the standard was more than 15 years ago (2001), and since that time, several deficiencies have been noted when using the standard for testing modern systems employing multiple-view and multiple-energy configurations. Accordingly, the present work describes a new revision of the ASTM F792 standard realized as a trifurcation into three parts, each with its own separate test object and associated test method. The three parts of the standard are intended for routine testing, human-perception testing, and objective technical testing, and represent a major update to this venerable standard.

Transmission X-ray systems are used to image the contents of suspicious packages, luggage, and cargo. The images can have a dynamic range of 1,000:1 or greater, but are typically displayed on consumer-grade displays with a low-dynamic range of less than 255:1. We show that modern tonemapping algorithms can greatly improve the process of displaying X-ray images on low-dynamic-range displays and compare the performance of some popular algorithms for this purpose.

We introduce a new technique for determining x-ray fluorescence line energies and widths, and we present measurements made with this technique of 22 x-ray L lines from lanthanide-series elements. The technique uses arrays of transition-edge sensors, microcalorimeters with high energy-resolving power that simultaneously observe both calibrated x-ray standards and the x-ray emission lines under study. The uncertainty in absolute line energies is generally less than 0.4 eV in the energy range of 4.5 keV to 7.5 keV. Of the seventeen line energies of neodymium, samarium, and holmium, thirteen are found to be consistent with the available x-ray reference data measured after 1990; only two of the four lines for which reference data predate 1980, however, are consistent with our results. Five lines of terbium are measured with uncertainties that improve on those of existing data by factors of two or more. These results eliminate a significant discrepancy between measured and calculated x-ray line energies for the terbium L l line (5.551 keV). The line widths are also measured, with uncertainties of 0.6 eV or less on the full-width at half-maximum in most cases. These measurements were made with an array of approximately one hundred superconducting x-ray microcalorimeters, each sensitive to an energy band from 1 keV to 8 keV. No energy-dispersive spectrometer has previously been used for absolute-energy estimation at this level of accuracy. Future spectrometers, with superior linearity and energy resolution, will allow us to improve on these results and expand the measurements to more elements and a wider range of line energies.

The structure of the x-ray emission lines of the Cu K α complex has been remeasured on a newly commissioned instrument, in a manner directly traceable to the Système Internationale definition of the meter. In this measurement, the region from 8000 to 8100 eV has been covered with a highly precise angular scale, and well-defined system efficiency, providing accurate wavelengths and relative intensities. This measurement updates the standard multi-Lorentzian-fit parameters from Härtwig, Hölzer, et al, and is in modest disagreement with their results for the wavelength of the K α 1 line when compared via quadratic fitting of the peak top; the intensity ratio of K α 1 to K α 2 agrees within the combined error bounds. However, the position of the fitted top of K α 1 is very sensitive to the fit parameters, so it is not believed to be a robust value to quote without further qualification. We also provide accurate intensity and wavelength information for the so-called K α 3,4 ‘satellite’ complex. Supplementary data, available online at stacks.iop.org/JPB/50/115004/mmedia, is provided which gives the entire shape of the spectrum in this region, allowing it to be used directly in cases where simplified, multi-Lorentzian fits to it are not sufficiently accurate.

Precision lattice spacing comparison measurements at the National Institute of Standards and Technology (NIST) provide traceability of X-ray wavelength and powder diffraction standards to the international system of units (SI). Here, we both summarize and document key measurements from the last two decades on six lots of intrinsic float-zone silicon, including unpublished results and recent internal-consistency checks. The comparison measurements link the unknown lattice spacing of a test crystal to a standard crystal for which the lattice spacing has been accurately determined by X-ray/optical interferometry in units traceable to the definition of the meter. The crystal that serves as the standard in all the comparisons is WASO 04, for which the lattice spacing is known with a relative uncertainty of 5 × 10−9. Individual lattice spacing comparison results have typical uncertainties of 1 ×10−8; taking material variability into account, measurements yield relative uncertainties for the test materials of a few tens of nanometers. It is observed that in the case of nearly perfect modern intrinsic float-zone silicon, the variability of the lattice spacing is sufficiently small that for most diffraction applications, a recommended reference value may be used.

An x-ray spectrometer employing a thin (50 μm) silicon transmission crystal was used to record high-resolution Cu Kα spectra from a laboratory x-ray source. The diffraction was from the (331) planes that were at an angle of 13.26° to the crystal surface. The components of the spectral lines resulting from single-vacancy (1s) and double-vacancy (1s and 3d) transitions were observed. After accounting for the natural lifetime widths from reference double-crystal spectra and the spatial resolution of the image plate detector, the intrinsic broadening of the transmission crystal was measured to be as small as 0.67 eV and the resolving power 12 000, the highest resolving power achieved by a compact (0.5 m long) spectrometer employing a single transmission crystal operating in the hard x-ray region. By recording spectra with variable source-to-crystal distances and comparing to the calculated widths from various geometrical broadening mechanisms, the primary contributions to the intrinsic crystal broadening were found to be the source height at small distances and the crystal apertured height at large distances. By reducing these two effects, using a smaller source size and vignetting the crystal height, the intrinsic crystal broadening is then limited by the crystal thickness and the rocking curve width and would be 0.4 eV at 8 keV energy (20 000 resolving power).

Experiments were performed at the LLNL Titan laser to measure the propagation direction of the energetic electrons that were generated during the interaction of the polarized laser beam with solid targets in the case of normal incidence. The energetic electrons propagated through vacuum to spectator metal wires in the polarization direction and in the perpendicular direction, and the K shell spectra from the different wire materials were recorded as functions of the distance from the laser focal spot. It was found that the fluence of the energetic electrons driven into the spectator wires in the polarization direction compared to the perpendicular direction was larger and increased with the distance from the focal spot. This indicates that energetic electrons are preferentially driven in the direction of the intense oscillating electric field of the incident laser beam in agreement with the multiphoton inverse Bremsstrahlung absorption process.

The ability to detect wires is an important capability of the cabinet x-ray imaging systems that are used in aviation security as well as the portable x-ray systems that are used by domestic law enforcement and military bomb squads. A number of national and international standards describe methods for testing this capability using the so called useful penetration test metric, where wires are imaged behind different thicknesses of blocking material. Presently, these tests are scored based on human judgments of wire visibility, which are inherently subjective. We propose a new method in which the useful penetration capabilities of an x-ray system are objectively evaluated by an image processing algorithm operating on digital images of a standard test object. The algorithm advantageously applies the Radon transform for curve parameter detection that reduces the problem of wire detection from two dimensions to one. The sensitivity of the wire detection method is adjustable and we demonstrate how the threshold parameter can be set to give agreement with human-judged results. The method was developed to be used in technical performance standards and is currently under ballot for inclusion in an international aviation security standard.

A Cauchois transmission-crystal spectrometer has been developed with high crystal resolving power in the 6 keV–15 keV energy range and sufficient sensitivity to record single-shot spectra from the Lawrence Livermore National Laboratory (LLNL) Titan laser and other comparable or more energetic lasers. The spectrometer capabilities were tested by recording the W L transitions from a laboratory source and the extended x-ray absorption fine structure (EXAFS) spectrum through a Cu foil.

We describe a simple method for high-precision rotary angle encoder calibration for long-range angular errors. By using a redesigned electronic nulling autocollimator, an optical-polygon artifact is calibrated simultaneously with determining the encoder error function over a rotation of 2π rad. The technique is applied to the NIST vacuum double crystal spectrometer, which depends on precise measurement of diffraction angles to determine absolute x-ray wavelengths. By oversampling, the method returned the encoder error function with an expanded uncertainty (k = 2) of 0.004 s of plane angle. Knowledge of the error function permits the instrument to make individual encoder readings with an accuracy of 0.06 s (k = 2), which is limited primarily by the least count and noise of the encoder electronics. While the error function lay within the nominal specifications, it differed from the intrinsic factory curve, indicating the need for in situ calibration in high-precision applications.

The tungsten L-gamma transitions between 11 and 12 keV and K alpha transitions from 57 to 60 keV were produced by a laboratory electron-bombarded x-ray source and simultaneously recorded with high resolution by using multiple diffraction planes of the same quartz crystal operating in Cauchois transmission geometry. The W K alpha transitions were dispersed by the (5 0 2) planes, which were perpendicular to the crystal entrance surface, and by the (6 0 2), (7 0 2), and (8 0 4) planes which were rotated with respect to the (5 0 2) planes by angles up to 4.80 degrees. The WL gamma transitions were dispersed by the (2 0 1) planes rotated from the (5 0 2) planes by 4.01 degrees. The spectra from the five planes were simultaneously recorded on image plate detectors, and spectra were also recorded by scanning solid-state electronic detectors with narrow slits across the spectral lines. The metrology of the L and K shell spectra diffracted from multiple quartz planes enabled the detailed analysis of the detector spatial resolution and accurate measurement of the instrumental broadening produced by the various quartz diffraction planes. The W L-gamma spectra had the highest instrumental resolving power, 1800, permitting for the first time the resolution of the blended L-gamma 4' (L1O2) and L-gamma 4 (L1O3) transitions. After subtracting the instrumental and detector contributions to the line widths, the remainder was assigned to the natural line widths. The measured widths of the O2 and O3 levels were 2.9 eV and 1.9 eV, respectively, and based on atomic code calculations these widths are attributed to the O2O3O4 and O3O4O5 super Coster-Kronig processes. This work demonstrates the ability to simultaneously record high resolution (< 1 eV) L and K spectra to determine the line shapes of the heavy elements (e.g. W through Am) by using multiple planes of a single quartz crystal and to accurately measure the non-radiative super Coster-Kronig rates which are closely related to the energy level structure of the outer shells of the heavy elements.

We discuss the first absolute energy measurements of the intercombination and forbidden transitions (x, y, z) in trapped Ti20+ ions to 15 parts per million accuracy. We present new measurements on helium-like titanium, in which the orbital radius is reduced and QED terms are magnified by the increased nuclear charge. The measured transition energies are higher than predicted.

Ultra-thin curved transmission crystals operating in the Cauchois spectrometer geometry were evaluated for the purpose of achieving high spectral resolution in the 6-13 keV x-ray energy range. The crystals were silicon (111) and sapphire R-cut wafers, each 18 μm thick, and a silicon (100) wafer of 50-μm thickness. The W Lα(1) spectral line at 8.398 keV from a laboratory source was used to evaluate the resolution. The highest crystal resolving power, E/ΔE=6300, was achieved by diffraction from the (33-1) planes of the Si(100) wafer that was cylindrically bent to a radius of curvature of 254 mm, where the (33-1) planes have an asymmetric angle of 13.26° from the normal of the crystal surface facing the x-ray source. This work demonstrates the ability to measure highly resolved line shapes of the K transitions of the elements Fe through Kr and the L transitions of the elements Gd through Th using a relatively compact spectrometer optical system and readily available thin commercial wafers. The intended application is as a diagnostic of laser-produced plasmas where the presence of multiple charged states and broadenings from high temperature and density requires high-resolution methods that are robust in a noisy source environment.