High Flux Mode Research Articles

Optimisation of a neutron imaging system using the modulation transfer function

The use of the modulation transfer function was explored for the characterisation and optimisation of the optical system used for tomographic imaging on the DINGO instrument at the Australian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organisation, Lucas Heights, Australia. Both a Siemens star and a phantom were used to determine the modulation transfer function and the results are compared. This allowed the optimal configuration of the instrument to be determined and the establishment of a relationship between sample dimension, exposure time and radiograph resolution to be developed. For tomographic studies of large samples, best results were achieved with DINGO configured in high-flux mode (L/D = 500), with a 6LiF/ZnS scintillator screen, an Iris 15TM sCMOS detector, a 50 mm lens, and an exposure time between 4 and 8 s.

Ca2+ efflux facilitated by co-transport of inorganic phosphate anion in the H+/Ca2+ antiporter YfkE

Ca2+ is an important signaling messenger. In microorganisms, fungi, and plants, H+/Ca2+ antiporters (CAX) are known to play key roles in the homeostasis of intracellular Ca2+ by catalyzing its efflux across the cell membrane. Here, we reveal that the bacterial CAX homolog YfkE transports Ca2+ in two distinct modes: a low-flux H+/Ca2+ exchange mode and a high-flux mode in which Ca2+ and phosphate ions are co-transported (1:1) in exchange for H+. Coupling with phosphate greatly accelerates the Ca2+ efflux activity of YfkE. Our studies reveal that Ca2+ and phosphate bind to adjacent sites in a central translocation pathway and lead to mechanistic insights that explain how this CAX alters its conserved alpha-repeat motifs to adopt phosphate as a specific “transport chaperon” for Ca2+ translocation. This finding uncovers a co-transport mechanism within the CAX family that indicates this class of proteins contributes to the cellular homeostasis of both Ca2+ and phosphate.

BioRef II-Neutron reflectometry with relaxed resolution for fast, kinetic measurements at HZB.

We present an upgrade to the time-of-flight neutron reflectometer BioRef at the research reactor BER II of the Helmholtz-Zentrum Berlin für Materialien und Energie (HZB). Through the integration of an additional chopper into the existing setup, the available wavelength resolution is significantly extended. Now two distinct operation modes can be used: a high resolution mode with Δλ/λ ranging from 1% to 5%, which allows for the investigation of thick films up to 4000 Å, and a high flux mode with Δλ/λ = 7%-11%. In the high flux mode, reflectivity curves from 0.007 Å-1 to 0.2 Å-1 with three angular settings can be recorded in 7 min. For a single angular setting and its respective window in Q-space, a time resolution of even less than 4 min is reached. The different configurations are documented by respective measurements (a) on a Ni-Ti multilayer and (b) the swelling kinetics of a solid-supported phospholipid coating upon incubation in a polyelectrolyte solution.

TAIPAN: First Results from the Thermal Triple-axis Spectrometer at OPAL Research Reactor

The thermal triple-axis spectrometer TAIPAN is the first instrument for inelastic neutron scattering at the new Australian research reactor OPAL. TAIPAN started operation in February 2009 and is in full user service since November 2010. Conceptually, it is similar to the triple-axis spectrometers IN8 (ILL) and PANDA (FRM-II) with variable incident and final energies and a secondary spectrometer with a single detector. The instrument can be operated either in a high flux mode with a double-focusing monochromator and analyser, or with Soller collimators - gaining resolution at the expense of intensity. Presently the PG (002) double-focusing monochromator and analyser are in use. The incident energy range on the TAIPAN TAS is from ∼5 meV up to ∼100 meV with neutron flux at sample position of 2.4≤107 n/cm2/s at incident energy of 14.8 meV. First experiments were performed with superionic conductor Cu2−δSe. The measurements reveal the presence of a soft mode related to ordering of Cu atoms followed by α - β phase transition at a lower temperature. The evolution of the magnetic structure with temperature in a magnetically modulated FePt3 thin film was investigated in the diffraction mode of TAIPAN. The results show that the film fabricated by modulation of the chemical order parameter consists of a magnetic FM/AFM superlattice in single-crystalline FePt3. The spin wave and phonon dispersion was recently investigated in TbVO3 single crystal. The acoustic and optical magnon branches were observed in the same energy range. This indicates that the 'orbital Peiers state' also exists in TbVO3.

TAIPAN: Thermal Triple-Axis Spectrometer

The thermal triple-axis spectrometer TAIPAN [1, 2] is the first instrument for inelastic neutron scattering at the new Australian research reactor OPAL. It is currently in the final stages of commissioning. Conceptually, it is similar to the triple-axis spectrometers (TAS) IN8 (ILL) and PANDA (FRM-II) with variable incident and final energies and a secondary spectrometer with a single detector. The instrument can be operated either in a high flux mode with a double-focusing monochromator and analyser, or with Søller collimators-gaining resolution at the expense of intensity.

Correction and alignment strategies for the beam separator of the photoemission electron microscope 3 (PEEM3)

A high-resolution aberration-corrected photoemission electron microscope (PEEM3) will be installed on an undulator beamline at the Advanced Light Source at the Lawrence Berkeley National Laboratory. The aim of this instrument is to provide a substantial flux and resolution improvement by employing an electron mirror for correcting both the third-order spherical aberration and the primary chromatic aberration. In order to utilize this concept of correction, a beam separator is a prerequisite. Crucial to achieving a resolution of 5nm for the high-resolution mode, and a 16-fold increase in throughput at the same resolution as its predecessor, PEEM2, specified as 20nm at 2% transmission, for the high flux mode is the double-symmetric design of the beam separator, which eliminates all the second-order geometric aberrations. Nonetheless, substantial tuning capabilities must be incorporated into the PEEM3 design to compensate for both systematic and random errors. In this article, we investigate how to correct for nonsystematic imperfections and for systematic uncertainties in the accuracy of the magnetic fields and focus on how degradation of the resolution and the field of view can be minimized. Finally, we outline a tentative correction strategy for PEEM3.

Polarized high-brilliance and high-resolution soft x-ray source at ELETTRA: The performance of beamline BACH

BACH, a soft x-ray beamline for polarization-dependent experiments at the Italian synchrotron radiation facility ELETTRA, was recently completed and characterized. Its performance, in terms of energy resolution, flux and polarization, is presented. Based on two APPLE II undulators, BACH covers the energy range between 35 and 1600 eV with the control of the light polarization. The monochromator is equipped with four gratings and allows one to work either in a high resolution or in a high flux mode. After the monochromator, the beamline is split into two branches with different refocusing properties. One is optimized to exploit the performance of the soft x-ray spectrometer (ComIXS) available at the beamline. Resolving powers between 12000 at 90 eV photon energy and 6600 near 867 eV were achieved using the high-resolution gratings and the smallest available slit width (10 μm). For the high-brilliance grating, which works between 290 and 1600 eV, resolving powers between 7000 at 400 eV and 2200 at 867 eV were obtained. The flux in the experimental chamber, measured with the high-resolution gratings for linearly polarized light at the best achievable resolution, ranges between 4×1011 photons/s at 125 eV and 2×1010 photons/s between 900 and 1250 eV. In circularly polarized mode the flux is two times larger for energies up to 380 eV. A gain of nearly one order of magnitude is obtained for the high-brilliance grating, in accordance with theoretical predictions. Flux beyond 1.3×1011 photons/s was measured up to 1300 eV, and thus over nearly the complete energy range covered by this high-brilliance grating, with a maximum of 1.6×1011 photons/s between 800 and 1100 eV. First results from polarization measurements confirm a polarization above 99.7% for both linearly and circularly polarized modes at low energies. Circular dichroism experiments indicate a circular polarization beyond 90% at the Fe L2/L3 edge near 720 eV.

Plane-grating monochromator at BESSY II using collimated light.

At the German synchrotron radiation facility BESSY II, the VUV photon energy range between 15 and 600 eV is covered by the first, third and fifth harmonics of the U125 undulator. The beamline connected to this source is a plane-grating monochromator (PGM) with a variable deviation angle. The plane grating is illuminated by collimated radiation, allowing very flexible use of the monochromator. Depending on users' demands, it can be operated at high spectral resolution, high-order suppression or in high-flux mode, simply by software control.