High-resolution Crystal Spectrometer Research Articles

Coronary angiography using laser plasma sources: X-ray source efficiency and optimization of a bent crystal monochromator

A monochromator has been developed for coronary angiography, comprising a single bent crystal of silicon in Laue transmission geometry. K spectra of laser irradiated solid tin and tantalum (Z=50 and 73, respectively) targets were measured. The high resolution crystal spectrometer resolve the Sn and Ta Kα doublets, allowing in a proof-of-principle experiment the absolute Kα photon numbers emitted by the source to be determined. The Ta Kα yield is measured as a function of the laser pulse energy, allowing an assessment to be made of the suitability of such sources for medical applications.

Dielectronic satellite contributions to Ne VIII and Ne IXK-shell spectra

K{alpha} spectra of heliumlike neon and associated lithiumlike, berylliumlike, and boronlike satellite line emission have been observed with a high-resolution crystal spectrometer on the Lawrence Livermore Electron Beam Ion Trap. The KLL dielectronic recombination satellites were resolved from their He-like parent lines in electron energy space, and their wavelengths and resonance strengths measured. The wavelength measurements achieved a typical accuracy of a few mAa, with two measurements accurate to better than one part in 10000. By normalizing to the He-like resonance line, w, we measure Li-like satellite resonance strengths that are 10% to 46% lower than predicted by theoretical models. The wavelengths and relative strengths of Be-like KLL satellites were also measured, and absolute strengths were obtained by normalizing to the collisionally excited Li-like qr satellite blend.

Measurement of central toroidal rotation in ohmic Tore Supra plasmas

The first simultaneous measurements of the toroidal rotation velocities of main (D+) and heavy impurity (Cr22+) ions in the core of ohmic plasmas are presented. For the main ions a system of five neutral particle (charge exchange) analysers is used, one having a near tangential line of sight. The velocities of the Cr22+ ions are obtained from the Doppler shift of X ray lines observed with a high resolution crystal spectrometer. Both ion species move in the direction opposite to the plasma current. The velocities are in the range 20-40 km/s. There is a strong indication that the toroidal motion is driven by the radial electric field created by ripple losses, as expected from neoclassical transport theory.

The GRID Technique: Current Status and New Trends.

In the GRID technique one measures Doppler-broadened line profiles of γ transitions using the high resolution crystal spectrometers GAMS, which are installed at the high flux reactor of the ILL Grenoble. One of the essential applications of this technique is the measurement of nuclear state lifetimes. In the present contribution the precision and the principal limits of the technique are discussed.

X-Ray Spectroscopy at the TEXTOR-94 Tokamak

Spectra of the 1s-2p resonance line of helium-like argon, Ar XVII, and the associated satellites in the narrow wavelength range from 3.9494 Å to 3.9944 Å have been observed at TEXTOR-94 with two high-resolution x-ray crystal spectrometers at Bragg angles near 54 degrees. Together, these instruments can be used as an x-ray polarimeter. The instruments are very sensitive to small amounts of argon; thus, a count rate of 4 × 105 photons/s, which corresponds to the maximum count rate capability of the presently used detectors, can be obtained for argon densities of less than 10-3 times the electron density, if the central electron temperature is about 1 keV. Up to 8192 spectra per discharge can be recorded allowing for the investigation of fast events during MHD activities. The instruments have been used to study the electron and ion behavior during internal sawtooth oscillations, which affect the confinement properties in the core of the plasma.The x-ray polarimeter at TEXTOR-94 is a unique diagnostic tool for the measurement of non-Maxwellian electron-velocity distributions, which can be produced in tokamak discharges in the presence of electric fields. First polarization measurements were performed during the flat-top phase in discharges with both pure ohmic heating and additional neutral-beam heating. These measurements showed that inhomogeneities in the emissivity profile can produce effects which look like polarization effects. No polarization was found when these source inhomogeneities were taken into account.The polarimeter is presently upgraded by an imaging x-ray crystal to facilitate polarization measurements. This will be important for the upcoming experiments with electron cyclotron heating at TEXTOR-94.

Wide-band, high-resolution soft x-ray spectrometer for the Electron Beam Ion Trap

We have constructed two wide-band, high-resolution vacuum flat crystal spectrometers and implemented them on the Electron Beam Ion Trap located at the Lawrence Livermore National Laboratory. Working in unison, these spectrometers can measure an x-ray bandwidth ⩽9 Å in the soft x-ray region below 21 Å. In order to achieve this large bandwidth each spectrometer houses either two 125 mm × 13 mm × 2 mm RAP (rubidium acid phthalate, 2d=26.121 Å), two 114 mm × 13 mm × 2 mm TlAP (thallium acid phthalate, 2d=25.75 Å) crystals, or some combination thereof, for dispersion and two position sensitive proportional counters for detection of x rays. The spectrometers are used to measure wavelengths and relative intensities of the L-shell line emission from Fe XVII–XXIV for comparison with spectra obtained from astrophysical and laboratory plasmas. The wide wavelength coverage attainable by these spectrometers makes it possible to measure all the L-shell emission from a given iron ion species simultaneously.

Imaging x-ray crystal spectrometers for the National Spherical Torus Experiment

A new type of high-resolution x-ray imaging crystal spectrometers is described for implementation on the National Spherical Torus Experiment (NSTX) to provide spatially and temporally resolved data on the ion temperature, toroidal and poloidal plasma rotation, electron temperature, impurity ion-charge state distributions, and impurity transport. These data are derived from observations of the satellite spectra of heliumlike argon, Ar XVII, which is the dominant charge state for electron temperatures in the range from 0.4 to 3.0 keV and which is accessible to NSTX. Experiments at the Torus Experiment for Technology Oriented Research (TEXTOR) demonstrate that a throughput of 2×105 photons/s (corresponding to the count-rate limit of the present detectors) can easily be obtained with small, nonperturbing argon gas puffs of less than 1×10−3 Torr l/s, so that it is possible to record spectra with a small statistical error and a good time resolution (typically 50 and 1 ms in some cases). Employing a novel design, which is based on the imaging properties of spherically bent crystals, the spectrometers will provide spectrally and spatially resolved images of the plasma for all experimental conditions, which include ohmically heated discharges as well as plasmas with rf and neutral-beam heating. The conceptual design, experimental results on the focusing properties, and relevant spectral data from TEXTOR are presented.

High-resolution study of ion-inducedKα1,2x-ray spectra from high-Zelements

The $K{\ensuremath{\alpha}}_{1,2}$ x rays emitted from La, Tb, Ta, and U targets induced by proton nitrogen, and neon ion bombardment at incident energies between 15 and 28 MeV/nucleon have been measured with a high-resolution crystal spectrometer. The spectra reflect the decay of a K vacancy in the presence of multiple L, M, N,\dots{} shell ``spectator'' vacancies. The L-shell ionization probabilities for impact parameters in the interior of the target's K shell are extracted from the measured spectra and compared with extensive theoretical calculations of ionization probabilities, based on the semiclassical separate-atom perturbation theory [semiclassical approximation (SCA)]. The projectile velocity varies from 60% to 125% of the target L electron velocity, so we can compare experimental data with theoretical predictions as a function of the relative velocity. We find that wave-function effects play an important role for an accurate calculation of the ionization probability. The experimental results agree well with the SCA predictions when Hartree-Fock-type wave functions are used [variationally determined optimized potential (SCA-OPM)]. Relativistic hydrogenic wave functions (SCA-HYD) provide a reliable description of experimental data only in the case of the uranium target. The influence of electron capture and intrashell coupling is also calculated and discussed. An independent comparison of theoretical constructed spectra with the experimental ones confirms the validity of the SCA-OPM. The hole-hole angular momentum coupling between ``active'' and ``spectator'' holes has been observed as predicted.

New precision measurement of the pionic deuteriums-wave strong interaction parameters

The x rays of the pionic deuterium 2p-1s transition were measured with a high resolution crystal spectrometer including a cyclotron trap (a magnetic device to increase the pion stopping density) and a CCD (charge-coupled device) detector system. The 1s strong interaction shift ${\ensuremath{\epsilon}}_{1s}$ and total width ${\ensuremath{\Gamma}}_{1s}$ were determined from the position and line shape of the x-ray peak. The (complex) pionic deuterium s-wave scattering length ${a}_{{\ensuremath{\pi}}^{\ensuremath{-}}d}$ was deduced. Its real part was related to the pion-nucleon scattering lengths, and the isoscalar coupling constant for ${\ensuremath{\pi}}^{\ensuremath{-}}$ absorption was deduced from the imaginary part.

Measurements and modeling of electric-dipole-forbidden2p1/2−2p3/2transitions in fluorinelikeU81+through berylliumlikeU88+

We report the observation of electric-dipole-forbidden ${2p}_{1/2}{\ensuremath{-}2p}_{3/2}$ transitions in berylliumlike, boronlike, carbonlike, nitrogenlike, oxygenlike, and fluorinelike uranium. Our measurement identified nine magnetic dipole transitions, as well as one strong electric quadrupole transition in carbonlike ${\mathrm{U}}^{86+}$ that has not been observed in lower-Z ions because of collisional quenching. The measurement was carried out with a high-resolution crystal spectrometer, and an accuracy as good as 35 ppm was obtained in the determination of the transition energies. The transitions are significantly less affected by quantum electrodynamical effects than analogous electric-dipole-allowed transitions in these ions. The data thus provide benchmarks for theoretical approaches of electron-electron correlation effects in the high-Z limit $Z\ensuremath{\alpha}\ensuremath{\approx}1$ that complement earlier measurements of $2s\ensuremath{-}2p$ transitions in such highly charged ions. The accuracy of the present measurements, however, was sufficient to determine the residual contributions from quantum electrodynamics (about 2 eV) with an accuracy of 5%, i.e., with an accuracy comparable to that of the best measurements of such contributions to the $1s$ ground level in hydrogenic ${\mathrm{U}}^{91+}.$ The contributions from quantum electrodynamics are in large part due to the vacuum polarization terms. The ${2p}_{1/2}{\ensuremath{-}2p}_{3/2}$ transition energies thus provide a handle for testing the accuracy of vacuum polarization terms nearly independent of the terms arising from the electron self energy. Results from collisional-radiative calculations are presented that show that the forbidden lines are almost exclusively produced by indirect processes, i.e., radiative cascades, radiative electron capture, and the ionization of ${2p}_{1/2}$ electrons. This is in stark contrast to the electric dipole-allowed transitions, which are mostly populated by direct electron-impact excitation.

Experimental widths of Kα x-ray lines in solid-state 3d elements

Using a high-resolution x-ray crystal diffraction spectrometer, x-ray line widths of the Kα1,2 lines of Fe, Co, Ni and Cu were analysed. Thereby, an evolutionary strategy was used for spectrum deconvolution to determine the life-time governed contributions to the line widths. On this basis, L2–L3X Coster–Kronig widths are calculated and assumptions about the energetics of radiationless transitions are derived. © 1998 John Wiley & Sons, Ltd.

M-SHELL X-RAY TRANSITION RATES FOR HEAVY RARE EARTH ELEMENTS

Partial M-x-ray production cross sections, which have not been well investigated up to the present, were measured in detail for six heavy lanthanides; Dy , Ho , Er , Tm , Yb and Lu . As a result, it is found that intensities of Mα,β lines, which are dominant among all the M-x-rays, and (M1-N2, M1-N3, M2-N4) lines agree well with those predicted by theory. However, clear discrepancy is found for Mζ and Mγ x-rays. Although it was pointed out by a PIXE analysis with a high-resolution crystal spectrometer that special attention must be paid for an analysis of Mζ and Mγ lines, it is found from the present work that it is possible to perform quantitative analysis using Mα,β lines.

X-ray spectroscopy of the pionic deuterium atom

The low energy X-rays of the pionic deuterium 3 P-1 S transition were measured using a high resolution crystal spectrometer, together with a cyclotron trap (a magnetic device to increase the pion stopping density) and a CCD (charge-coupled device) detector system. The spectrometer resolution was 0.65 eV FWHM for a measured energy of approximately 3075 eV. This energy was measured with a precision of 0.1 eV. Compared to conventional methods, the cyclotron trap allowed for a gain in stopping density of about an order of magnitude. The CCDs had excellent spatial and energy resolutions. Non-X-ray background could therefore be almost completely eliminated. The 1 S strong interaction shift ϵ 1 S and total decay width Γ 1 S were determined from the position and line shape of the X-ray peak. They are ϵ 1S( shift) = 2.43 ± 0.10 eV ( repulsive), Γ 1S( width) = 1.02 ± 0.21 eV , where the statistical and systematic errors were added linearly. The total (complex) pionic deuterium S-wave scattering length a π − d was deduced: a π −d = −0.0259(±0.0011) + i0.0054(±0.0011)m π −1 . From the real part of a π − d a constraint in terms of the isoscalar and isovector πN′ scattering lengths b 0 and b 1 was deduced. From Im a π − d we determined the isoscalar coupling constant for π − absorption: | g 0| = (2.6 ± 0.3) 10 −2 m π −2. The experiments of the pionic hydrogen and deuterium S-wave scattering lengths were analyzed within the framework of a search for i isospin symmetry violation. The data are still compatible with isospin conservation. The scattering lengths deduced from the Karlsruhe-Helsinki phase shift analysis disagree with the present results.

A new determination of the pion mass

Initial measurements concerning the feasibility of a new pion mass determination are described. In a first step, a high-resolution crystal spectrometer was coupled to a cyclotron trap which provides a high pion stopping density, sufficient to check predictions for the cascade process and to measure the stability of the apparatus. A comparison with the measured Cu K α fluorescence line resolves an ambiguity in the value of the pion mass. The preliminary result from this experiment is m π − = (139.57040 ± 0.00045) MeV/c 2.

High-resolution study of the maxon-roton signal parameters in superfluid 4He

High-energy resolution (15 μeV) measurements of the maxon-roton signal parameters have been carried out on superfluid 4He by the high-resolution crystal analyser spectrometer (IRIS) at the ISIS Facility. These inverse-geometry TOF measurements performed in the liquid state within a range of pressures (1.1–24) bar and in the temperature range (1.4–1.8) K, cover the roton and maxon regions of the dynamic structure factor.

Development of high-resolution vacuum crystal spectrometer in a compact helical system and large helical device

A vacuum crystal spectrometer that covers a wavelength range of 1.0–2.5 nm has been developed to observe light (oxygen) and heavy (titanium and iron) impurities for large helical device (LHD) diagnostics. A Johann-type spectrometer (2 R = 60 cm and 3 m, RAP crystal, 2 d = 2.612 nm) was constructed and installed in a compact helical system (CHS). The O VII resonance line was successfully observed through a thin (3.3 μm t) polypropylene film, although the metallic impurity lines were not seen. In the case of a crystal with 2 R = 3 m, however, the spectral resolution λ/Δλ was limited to 440, whereas the replacement by the crystal with 2R = 60 cm improved the resolution to 610. The result is discussed with regard to the quality of the bent crystal.

The 112Cd laboratory: An extension. E0 strengths, multiphonon states and coupled vibrations

The structure of 112Cd was investigated using the 111Cd( n th, γ) and 110Pd(α,2n) reactions. High resolution crystal and magnetic spectrometers as well as different Compton-suppressed spectrometers were used. The results were combined with published data resulting in a complete level scheme over a large range of spins and excitation energies. The interpretation of the data was performed in the framework of the interacting boson model (IBM). A special effort was put in the interpretation of E0 data and an attempt was made to identify multiphonon and 2 1 + ⊗ 3 1 − states.

Application of chemical effects in X-ray spectra for characterization of the high-Tc superconductors

Abstract Chemical effects in X-ray spectra (energy shifts, emission probability changes, satellite formation and peak profile changes) may be used for characterization of the chemical circumstances and chemical bonding of the monitored element in the sample. For that purpose, an investigation of the chemical effects in ion induced X-ray spectra of the high- T c superconductor materials Sr 2 Ln y Ce 0.5 TaCu 2 O 10+ δ ( Ln =Eu,Sm) was carried out using a high resolution crystal X-ray spectrometer. The applicability of the chemical effects for the mapping of the crystal phases in the superconductor sample using an ion microbeam is discussed.

A high-resolution transmission-type x-ray spectrometer designed for observation of the Kα transitions of highly charged high-Z ions

High-resolution reflection-type crystal spectrometers have been used for x-ray energies up to 13 keV, e.g., the K-shell radiation of heliumlike Kr. In order to extend crystal spectrometer measurements to higher energy x rays from higher-Z elements, we employ the crystal in transmission. The geometry we use is known as DuMond geometry. Using such a transmission-type crystal x-ray spectrometer, we have measured the K-shell radiation of various highly charged high-Z ions. In particular, we present a measurement of the 1s2p 1P1→1s2 1S0 transition in heliumlike xenon, Xe52+. For this transition, we measure a linewidth of 34 eV, which demonstrates that the resolving power we achieved with the new spectrometer is on the order of 1000.

The strong interaction shift and width of the ground state of pionic hydrogen

The 3p-1s transition in pionic hydrogen was investigated with a high-resolution crystal spectrometer system. From the precisely measured transition energy, together with the (calculated) electromagnetic energy, the strong interaction shift of the 1s state was obtained as ϵ 1s = −7.127 ± 0.028(stat.)± 0.036(syst.) eV (attractive). From the natural line width, measured for the first time, we determine the decaywidth of the 1s state: Γ 1s (decay) = 0.97 ± 0.10(stat.)± 0.05(syst.) eV. With the recently calculated electromagnetic corrections the s-wave scattering lengths of an isospin symmetric strong interaction are deduced. The scattering length for elastic scattering of a negative pion on a proton is a π − p→ π − p h = 0.0885±0.00003(stat.)±0.0006(syst.) m π −1. The scattering lengthe for single charge exchange is found to be a π − p→ π 0 n h = −0.136 ± 0.007(stat.) ± 0.003(syst.) m π −1. The experiment was performed at the Paul Scherrer Institute (PSI) in Switzerland. A focussing crystal spectrometer with an array of bent crystals, the cyclotron trap (a magnetic system designed to increase the particle stop density) and a CCD (charge-coupled device) detector system were employed. The results from the pionic hydrogen experiment — together with those from the pionic deuterium experiment — were used to test the isospin symmetry of the strong interaction. The present data are still consistent with isospin sysmmetry.