High efficiency and low absorption Fresnel compound zone plates for hard X-ray focusing

Circular and linear zone plates have been fabricated on the surface of silicon crystals for the energy of 8 keV by electron beam lithography and deep ion plasma etching methods. Various variants of compound zone plates with first, second, third diffraction orders have been made. The zone relief height is about 10 mkm, the outermost zone width of the zone plate is 0.4 mkm. The experimental testing of the zone plates has been conducted on SPring-8 and ESRF synchrotron radiation sources. A focused spot size and diffraction efficiency measured by knife-edge scanning are accordingly 0.5 mkm and 39% for the first order circular zone plate.Comment: 5 pages, 7 figure

The relationship of protein conservation and sequence length

BACKGROUND: In general, the length of a protein sequence is determined by its function and the wide variance in the lengths of an organism's proteins reflects the diversity of specific functional roles for these proteins. However, additional evolutionary forces that affect the length of a protein may be revealed by studying the length distributions of proteins evolving under weaker functional constraints. RESULTS: We performed sequence comparisons to distinguish highly conserved and poorly conserved proteins from the bacterium Escherichia coli, the archaeon Archaeoglobus fulgidus, and the eukaryotes Saccharomyces cerevisiae, Drosophila melanogaster, and Homo sapiens. For all organisms studied, the conserved and nonconserved proteins have strikingly different length distributions. The conserved proteins are, on average, longer than the poorly conserved ones, and the length distributions for the poorly conserved proteins have a relatively narrow peak, in contrast to the conserved proteins whose lengths spread over a wider range of values. For the two prokaryotes studied, the poorly conserved proteins approximate the minimal length distribution expected for a diverse range of structural folds. CONCLUSIONS: There is a relationship between protein conservation and sequence length. For all the organisms studied, there seems to be a significant evolutionary trend favoring shorter proteins in the absence of other, more specific functional constraints

Deterministic retrieval of surface waviness by means of topography with coherent X-rays

A surface profile retrieval technique from multiple X-ray total reflection images taken at various distances with full coherent illumination is demonstrated. An experiment was performed using the 1 km-long BL29XU beamline at the SPring-8 facility, Japan. Obtained results are compared with results from the optical metrology technique (Fizeau's interferometer). Good agreement between X-ray and optical methods proves the validity of the current approach. Meanwhile, the sensitivity of the X-ray technique is several times higher than that of the standard one. This technique is well suited to the needs of characterizing grazing optics for new-generation X-ray sources.Souvorov, A., Yabashi, M., Tamasaku, K., Ishikawa, T., Mori, Y., Yamauchi, K., Yamamura, K. & Saito, A. (2002). J. Synchrotron Rad. 9, 223-228

Aging Studies for the Large Honeycomb Drift Tube System of the Outer Tracker of HERA-B

The HERA-B Outer Tracker consists of drift tubes folded from polycarbonate foil and is operated with Ar/CF4/CO2 as drift gas. The detector has to stand radiation levels which are similar to LHC conditions. The first prototypes exposed to radiation in HERA-B suffered severe radiation damage due to the development of self-sustaining currents (Malter effect). In a subsequent extended R&D program major changes to the original concept for the drift tubes (surface conductivity, drift gas, production materials) have been developed and validated for use in harsh radiation environments. In the test program various aging effects (like Malter currents, gain loss due to anode aging and etching of the anode gold surface) have been observed and cures by tuning of operation parameters have been developed.Comment: 14 pages, 6 figures, to be published in the Proceedings of the International Workshop On Aging Phenomena In Gaseous Detectors, 2-5 Oct 2001, Hamburg, German

X-ray scatter measurements from thermally slumped thin glass substrates for the HEFT hard x-ray telescopes

We have performed x-ray specular reflectivity and scattering measurements of thermally slumped glass substrates on x-ray diffractometers utilizing a rotating anode x-ray source at the Danish Space Research Institute (DSRI) and synchrotron radiation at the European Synchrotron Radiation Facility (ESRF) optics Bending Magnet beamline. In addition, we tested depth graded W/Si multilayer-coated slumped glass using x-ray specular reflectivity measurements at 8.048 keV and 28 keV and energy-dispersive measurements in the 20-50 keV rang at a double-axis diffractometer at the Orsted Laboratory, University of Copenhagen. The thermally slumped glass substrates will be used to fabricate the hard x-ray grazing incidence optics for the High-Energy Focusing Telescope. We compared the measurements to the SODART- mirrors from the SRG telescope mission program. The surface scatter measurement of the thermally slumped glass substrates yields Half Power Diameters (HPD's) of single- bounce mirrors of full-illuminated lengths of ~ 40 arcseconds for typical substrates and as low as ~ 10 arcseconds for the best substrates, whereas the SODART mirrors yields HPD's of ~ 80 arcseconds with very little variation. Both free-standing glass substrates and prototype mounted and multilayer-coated optics were tested. The result demonstrate that the surface scatter contribution, plus any contribution from the mounting procedure, to the Half Power Diameter from a telescope using the slumped glass optics will be in the subarcminute range.In addition we measured low surface microroughness, yielding high reflectivity, from the glass substrates, as well as from the depth graded W/Si multilayer-coated glass glass (interfacial width 4.2 Å)

The Outer Tracker Detector of the HERA-B Experiment Part I: Detector

The HERA-B Outer Tracker is a large system of planar drift chambers with about 113000 read-out channels. Its inner part has been designed to be exposed to a particle flux of up to 2.10^5 cm^-2 s^-1, thus coping with conditions similar to those expected for future hadron collider experiments. 13 superlayers, each consisting of two individual chambers, have been assembled and installed in the experiment. The stereo layers inside each chamber are composed of honeycomb drift tube modules with 5 and 10 mm diameter cells. Chamber aging is prevented by coating the cathode foils with thin layers of copper and gold, together with a proper drift gas choice. Longitudinal wire segmentation is used to limit the occupancy in the most irradiated detector regions to about 20 %. The production of 978 modules was distributed among six different laboratories and took 15 months. For all materials in the fiducial region of the detector good compromises of stability versus thickness were found. A closed-loop gas system supplies the Ar/CF4/CO2 gas mixture to all chambers. The successful operation of the HERA-B Outer Tracker shows that a large tracker can be efficiently built and safely operated under huge radiation load at a hadron collider.Comment: 28 pages, 14 figure

The Outer Tracker Detector of the HERA-B Experiment. Part II: Front-End Electronics

The HERA-B Outer Tracker is a large detector with 112674 drift chamber channels. It is exposed to a particle flux of up to 2x10^5/cm^2/s thus coping with conditions similar to those expected for the LHC experiments. The front-end readout system, based on the ASD-8 chip and a customized TDC chip, is designed to fulfil the requirements on low noise, high sensitivity, rate tolerance, and high integration density. The TDC system is based on an ASIC which digitizes the time in bins of about 0.5 ns within a total of 256 bins. The chip also comprises a pipeline to store data from 128 events which is required for a deadtime-free trigger and data acquisition system. We report on the development, installation, and commissioning of the front-end electronics, including the grounding and noise suppression schemes, and discuss its performance in the HERA-B experiment

Inclusive V0V^0 Production Cross Sections from 920 GeV Fixed Target Proton-Nucleus Collisions

Inclusive differential cross sections $d\sigma_{pA}/dx_F$ and $d\sigma_{pA}/dp_t^2$ for the production of \kzeros, \lambdazero, and \antilambda particles are measured at HERA in proton-induced reactions on C, Al, Ti, and W targets. The incident beam energy is 920 GeV, corresponding to $\sqrt {s} = 41.6$ GeV in the proton-nucleon system. The ratios of differential cross sections \rklpa and \rllpa are measured to be $6.2\pm 0.5$ and $0.66\pm 0.07$, respectively, for \xf $\approx-0.06$. No significant dependence upon the target material is observed. Within errors, the slopes of the transverse momentum distributions $d\sigma_{pA}/dp_t^2$ also show no significant dependence upon the target material. The dependence of the extrapolated total cross sections $\sigma_{pA}$ on the atomic mass $A$ of the target material is discussed, and the deduced cross sections per nucleon $\sigma_{pN}$ are compared with results obtained at other energies.Comment: 17 pages, 7 figures, 5 table