Hard X-ray Beamline Research Articles

X-ray scattering study of charge scattering associated with stripe order in La2NiO4

In this paper we report the first observation of stripe correlations of holes in hole-doped La2NiO4 by X-ray diffraction. The experiment was performed in Laue geometry at the hard X-ray beamline BW5 at HASYLAB on a crystal of La1.77Sr0.22NiO4 previously studied by neutron diffraction. Temperature dependences of the intensities and wave vectors of the charge-density-modulation peaks were characterized and found to be in good agreement with the neutron scattering results. Interestingly, weak, temperature-dependent scattering was also observed at positions consistent with nonresonant X-ray magnetic scattering from the spin correlations; however, a definitive determination of its origin remains lacking.

The Naval Research Laboratory’s new hard x-ray beamline at the National Synchrotron Light Source

The Naval Research Laboratory is currently rebuilding its hard x-ray beamline at the National Synchrotron Light Source (NSLS, X-23B) to increase the flux and energy range. The optical and mechanical design of the new configuration is described and its performance predicted. The new design contains a fixed-exit pair of mirrors for harmonic rejection and source collimation and a fixed-exit two-crystal monochromator with sagittally focusing second crystal. In addition, the horizontal acceptance of the line will be increased from 6 to 18 mrad. The line is expected to focus radiation to a spot 0.5 mm vertical by 1.0 mm horizontal in the energy range 2 to 30 keV. At 8.5 keV a throughput of 5.7×1012 photons/s/200 mA is expected with an E/ΔE of 5×103 with Si (111) crystals, a factor of 10 to 30 over present beamline throughput. The increased flux is due to improved mirror surfaces, decreased optical aberrations from conical sagittal focusing, and the increased horizontal acceptance.

SSRL 1990 — status and future plans

The present status and future directions of scientific, machine, and insertion device research at the Stanford Synchrotron Radiation Laboratory (SSRL) are reviewed. A central focus is on the transformation of SPEAR into a fully dedicated synchrotron radiation (SR) source with a dedicated 3 GeV injector synchrotron. Recently implemented upgrades of SPEAR are reviewed and a summary of the March/April (1990) run is given. Effects of the October 1989 earthquake on SPEAR and PEP are noted and the characterization and performance of the two hard X-ray beam lines on PEP are summarized.

Measurement of soft X-ray absorption spectra with a fluorescent ion chamber detector

The problem of absorption of soft X-rays by thick Be windows in hard X-ray beam lines is well known. Although the signal at 2.4 keV was reduced by ∼ 10 3 we have routinely measured the absorption spectra of S (2472 eV) and elements at higher energies including Cl, Ar and K. These spectra were obtained on hard X-ray beam lines at Stanford Synchrotron Radiation Laboratory (SSRL) with Si(111) monochromator crystals and a fluorescent ion chamber detector [1]. Higher energy harmonics were minimized by detuning and the end station was enclosed in a helium bag to prevent absorption by air. Although the diminished X-ray flux and decreasing fluorescent yield were serious negative factors at these low X-ray energies the spectra from thick samples were of excellent quality with sufficient sensitivity to characterize 1% S in coal. Representative spectra are shown comparing data from focused and unfocused beam lines and with S data from JUMBO [2]. Comparison of Ar and KCl data to excellent data found in the older literature [3–5] allow a confirmation of the resolution function (energy bandpass) of the monochromator. A simple new beam line is suggested which would allow a substantial increase in low energy X-ray flux (measurements down to Al and Si) with the sample and detector in a He atmosphere.