Hydrogen-like light muonic ions, in which one negative muon replaces all of the electrons, are extremely sensitive probes of nuclear structure. Using pulsed laser spectroscopy, we have measured three 2S-2P transitions in the muonic helium-3 (μ3He+) ion, an ion formed by a negative muon and bare helium-3 nucleus. This allowed us to extract the Lamb shift, the 2P fine structure splitting, and the 2S-hyperfine splitting in μ3He+. Comparing these measurements with theory, we determined the root-mean-square charge radius of the helion (3He nucleus) to be rh = 1.97007(94) fm, in good agreement with the value from elastic electron scattering but a factor 15 more accurate. Our results represent benchmarks for few-nucleon theories and open the way for precision quantum electrodynamics tests in He atoms and ions.

The NIST silicon lattice comparator has been in service, in various forms, since the 1970s. It is capable of measuring the difference in lattice spacing between specimens of high-quality float-zone silicon to Δd/d ≈ 6 × 10-9. It has recently undergone a thorough update of its control systems and mechanics. These upgrades result in the ability to collect data with improved stability, less settling time of the instrument, and less operator intervention.

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.

A Correction to this paper has been published: https://doi.org/10.1038/s41586-021-03360-2.

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.

We have measured the widths and energies of the 1s2s2p(2)P(1/2)(,)(3/2) -> 1s(2)2s(2)S(1/2) transitions in lithiumlike sulfur and argon, as well as the energies of the forbidden 1s2s2p(4)P(5/2) -> 1s(2)2s(2)S(1/2) M2 transition in both elements. All measurements were performed with a double-flat-crystal spectrometer without the use of any reference line. The transition energy measurements have accuracies ranging from 2.3 to 6.4 ppm depending on the element and line intensity. The widths and the intensity ratios of the 1s2s2p(2)P(1/2,3/2) -> 1s(2)2s(2)S(1/2) lines have also been measured. These are reference-free measurements of transitions in core-excited lithiumlike ions and have an accuracy comparable to the best relative measurements. We have also performed multiconfiguration Dirac-Fock calculations of the widths, energies, and intensity ratios. An extensive comparison between existing experimental results and theory is performed, and Bayesian techniques are employed to extract the energy of the 1s2p(2) P-4(1/2) -> 1s(2)2p(2)P(1/2) transition in sulfur and identify contaminant transitions.

High-resolution x-ray spectra were recorded at the National Institute of Standards and Technology electron beam ion trap (EBIT) using two Johann-type crystal spectrometers, with their dispersion planes oriented parallel and perpendicular to the beam direction. The linear polarizations of the 1s(2) - 1s2l transitions in He-like argon ions were determined from the measured spectra at electron beam energies of 3.87 and 7.91 keV. The theoretical analysis was performed using detailed collisional-radiative modeling of the non-Maxwellian EBIT plasma with the NOMAD code modified to account for magnetic sublevel atomic kinetics. Effects influencing the polarizations of the observed 1s(2 )- 1s2l lines were investigated, including radiative cascades, the 1s(2) S-1(0) - 1s2s S-1(0) two-photon transition, and the charge exchange recombination of H-like argon ions. With these included, the measured polarizations of the resonance (1s(2) S-1(0) - 1s2p P-1(1)), intercombination (1s(2) S-1(0) - 1s2p P-3(1)), and forbidden lines (1s(2) S-1(0) - 1s2s S-3(1), 1s(2) S-1(0) - 1s2p P-3(2) ) were found to be in good agreement with the calculations.

This work demonstrates efficient micro-lensing of laseraccelerated proton beams by transient electromagnetic (EM) fields in coil targets. In an all-optical principle, hig intensity ps-laser pulses are used to charge solid density t argets and induce EM target-discharges [1]. The strong transient EM-fields are guided by the target geometry. Such EM-mode propagation along wire targets [2] has already been used for the guiding of a proton beam [3]. Our collaboration aims at a more easily tunable energy-selective collimation and focusing with independent discharge and particle source targets: A sub-mm coil shaped part of the discharge target’s rod produces lensing effects. Protons with in an energy range of approximately ±2MeV, with energies up to12MeV, are focused over cm-scale distances.

Non-thermal electron distributions, such as beams of electrons, are found in many laboratory and astrophysical plasma sources and can produce anisotropic and polarized emission. Theories used to model the emission require sublevel specific analysis, which can be difficult to verify experimentally. Using two polarization-sensitive Johann-type crystal spectrometers at the National Institute of Standards and Technology (NIST) electron beam ion trap facility, we measured the linear polarization of well-known dielectronic recombination satellite transitions from Li-like Ar ions and two blended features from Be-like ions. The spectrometers observed the plasma at 90° relative to the electron beam propagation direction, and the crystal dispersion planes were oriented perpendicular relative to each other to allow for differing polarization sensitivities. Measurements were taken near the resonance energies of each line and compared with theoretical predictions based on relativistic magnetic sublevel atomic kinetics using the density-matrix theory. Most of the predictions are in excellent agreement with measured values.

We have measured the widths and energies of the 1s2s2p 2 P 1/2,3/2 → 1s 2 2s 2 S 1/2 transitions in lithiumlike sulfur and argon, as well as the energies of the forbidden 1s2s2p 4 P 5/2 → 1s 2 2s 2 S 1/2 M2 transition in both elements. All measurements were performed with a double-flat crystal spectrometer without the use of any reference line. The transition energy measurements have accuracies ranging from 2.3 ppm to 6.4 ppm depending on the element and line intensity. The widths and the intensity ratios of the 1s2s2p 2 P 1/2,3/2 → 1s 2 2s 2 S 1/2 lines have also been measured. These are the first reference-free measurements of transitions in core-excited lithiumlike ions, and have an accuracy comparable to the best relative measurements. We have also performed multi-configuration Dirac-Fock calculations of the widths, energies and intensity ratios. Extensive comparison between existing experimental results and theory is performed, and Bayesian techniques employed to extract the energy of the 1s 2p 2 4 P 1/2 → 1s 2 2p 2 P 1/2 transition in sulfur and identify contaminant transitions.

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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.

Accurate spectroscopy of highly charged high-Z ions in a storage ring is demonstrated to be feasible by the use of specially adapted crystal optics. The method has been applied for the measurement of the 1s Lamb shift in hydrogen-like gold (Au 78+) in a storage ring through spectroscopy of the Lyman x rays. This measurement represents the first result obtained for a high-Z element using high-resolution wavelength-dispersive spectroscopy in the hard x-ray regime, paving the way for sensitivity to higher-order QED effects.

The present article describes the design, the calibration and preliminary tests of the X-ray transmission crystal spectrometer SPECTIX (Spectromètre PEtal à Cristaux en Transmission X) built in the framework of the PETAL (PETawatt Aquitaine Laser) project and located in the Laser MégaJoule (LMJ) facility [1,2]. SPECTIX aims at characterizing the hard x-ray Kα emission generated by the interaction of the PETAL ps ultra high-energy laser with a target. The broad spectral range covered by this spectrometer (7 to 150 keV) is achieved by using two measurement channels composed by two distinct crystals. Due to the harsh environment experienced by the spectrometer during a LMJ-PETAL shot, passive detection with image plates is used. Shielding has been dimensioned in order to protect the detector against PETAL shot products. It includes a magnetic dipole to remove electrons entering the spectrometer, a 20 mm thick tungsten frontal collimation and a 6 mm thick lead housing. The SPECTIX performances, including the shielding efficiency, have been tested during an experimental campain performed at the PICO 2000 laser facility at LULI. Improvements inferred from these tests are currently being implemented. Full commissioning of SPECTIX is planned on PETAL shots at the end of 2017.

We present our results of x-ray transitions measurements from n=2 to n=1 in highly charged ions of argon using a double flat-crystal spectrometer [1]. The ions were produced in a plasma of an ECRIS (Electron-Cyclotron Resonance Ion Source). Two transitions in two different charge states of argon (Heand Be-like) have been measured with an accuracy better than 3 ppm [2]. The 1s2p 1P1 → 1s2 1S0 transition measurement confirms the recent reference-free measurement of the Heidelberg EBIT (Electron-Beam Ion Trap) [3] while the 1s2s22p 1P1→ 1s22s2 1S0 transition energy is the first reference-free measurement for a transition in an ion with more than two electrons. The natural widths have been also experimentally obtained by applying a fitting procedure to the experimental spectra that uses full Monte-Carlo simulated spectra and an experimental value for the Doppler broadening of the lines obtained in Ref. [4]. Both energies and widths are in agreement with the most advanced calculations. The accuracy in the ppm level provides tests of QED (Quantum Electrodynamics) and relativistic effects. It also provides accurate x-ray standards in narrow transitions of highly charged ions that can be used to calibrate instruments in this energy range. The experiment setup, the most recent results and the current status of the experiment will be presented focused in the DCS working principle and in the planned measurements and setup updates. [1] P. Amaro, et al. Radiation Physics and Chemistry, 98(C), 132–149 (2014) [2] J. Machado, et al. Accepted Phys. Rev. A, (15-02-2018). [3] K. Kubiçek, et al., Rev. Sci. Instrum. 83, 013102 (2012). [4] P. Amaro, et al. Phys. Rev. Lett. 109, 043005 (2012). * jfd.machado@fct.unl.pt

The double response of a large area avalanche photodiode, a planar RMD model S1315, to 6-keV x-rays was investigated as a function of APD biasing voltage and for different operating temperatures. Our data are consistent with the interpretation that the dissimilar APD response is due to x-ray interactions in the different APD-layer structures; interactions in the APD entrance layer just below the front electrode, where the electric field intensity is very low lead to pulses with higher risetime and lower amplitudes, when compared with interactions in the deeper layers where the electric field is more intense. Average pulse risetime values of 14 and 7 ns have been measured in our setup, the slower pulses presenting average amplitudes which are around 20% lower than those of the faster pulses. While the fast risetime does not depend significantly on APD biasing voltage and on temperature, the slow risetime presents a slight decrease with increasing bias voltage and decreasing temperature, a behaviour that is consistent with the increase of the electric field as a result of the increase in the APD biasing voltage. The fraction of the slow pulses reduces from 60% to 40% as the APD biasing increases from about 1.58 to 1.64 kV, indicating a reduction in the thickness, from 25 to 15 mu m, in the weak-electric-field entrance layer.

This research was supported in part by Projects No. PEstOE/FIS/UI0303/2011 and No. PTDC/FIS/117606/2010, and by research center Grant No. UID/FIS/04559/2013 (LIB-Phys), from FCT/MCTES/PIDDAC, Portugal. We acknowledge partial support from NIST (P.I.), from PESSOA Huber Curien Program No. 38028UD, and PAUILF Program No. 2017-C08. P.A., J.M., and M.G. acknowledge support from FCT under Contracts No. SFRH/BPD/92329/2013, No. SFRH/BD/52332/2013, and No. SFRH/BPD/92455/2013, respectively. Laboratoire Kastler Brossel (LKB) is "Unite Mixte de Recherche de Sorbonne Universite, de ENS-PSL Research University, du College de France et du CNRS No. 8552." P.I. is a member of the Allianz Program of the Helmholtz Association, Contract No. EMMI HA-216 "Extremes of Density and Temperature: Cosmic Matter in the Laboratory." The SIMPA ECRIS has been financed by grants from CNRS, MESR, and University Pierre and Marie Curie (now Sorbonne Universite). The experiment has been supported by BNM Grant No. 0130002 and ANR Grant No. ANR-06-BLAN-0223. We wish to thank Jean-Paul Desclaux for his help improving the MCDFGME code, and Dr. Martino Trassinelli (INSP) for valuable discussions and his help during early stages of the experiment.

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.