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A monochromatic computed tomography (CT) scanner is being developed at the X17 superconducting wiggler beamline at the National Synchrotron Light Source (NSLS), Brookhaven National Laboratory, to image the human head and neck. The system configuration is one of a horizontal fan beam and an upright seated rotating subject. The purposes of the project are to demonstrate improvement in the image contrast and in the image quantitative accuracy that can be obtained in monochromatic CT and to apply the system to specific clinical research programs in neuroradiology. This paper describes the first phantom studies carried out with a prototype system, using the dual photon absorptiometry (DPA) method at energies of 20 and 38 keV. The results show that improvements in image contrast and quantitative accuracy are possible with monochromatic DPA CT. Estimates of the clinical performance of the planned CT system are made on the basis of these initial results.

Measurements done recently at the NSLS have indicated that the level of intensity found in the wings of diffraction peaks from silicon at higher X-ray energies (> 20 keV) far exceeds the value which would be predicted based on the dynamical theory. We have measured Si(220) double crystal rocking curves at the 40 keV fundamental and harmonics with various crystal scattering geometries: Bragg-Bragg, Laue-Bragg, Laue-Laue. The comparison of the Bragg and Laue case diffraction geometries was done to determine scattering volume effects. Comparisons with dynamical theory calculations will be discussed. These measurements have been carried out in order to assess the level of harmonic contamination which will be present from a double crystal monochromator being designed for the X17 superconducting wiggler beamline.

A high‐energy double‐crystal x‐ray monochromator has been constructed for use on the X‐17 beam line at the National Synchrotron Light Source (NSLS). Its design is based on the ‘‘boomerang’’ right angle linkage, and features a fixed exit beam, a cooled first crystal, and an energy range of 8–92 keV. The entire mechanism is UHV compatible. The design is described and performance details, obtained in testing at the X17 beam line, are presented.

The Synchrotron Medical Research Facility (SMERF) at the National Synchrotron Light Source has been completed and is operational for human coronary angiography experiments. The imaging system and hardware have been brought to SMERF from the Stanford Synchrotron Radiation Laboratory where prior studies were carried out. SMERF consists of a suite of rooms at the end of the high‐field superconducting wiggler X17 beam line and is classified as an Ambulatory Health Care Facility. Since October of 1990 the coronary arteries of five patients have been imaged. Continuously improving image quality has shown that a large part of both the right coronary artery and the left anterior descending coronary artery can be imaged following a venous injection of contrast agent.

Dual-energy CT imaging of the brain will be performed using synchrotron radiation X-ray beams at about 40 and 80 keV to visualize the altered concentrations of the intermediate-Z elements that occur in brain lesions and atherosclerotic plaques. The monochromator designs considered allow rapid switching between these two energies without change in the position or direction of the X-ray beam. One design uses the fundamental and second harmonic radiations from an existing dual-Bragg-crystal Si〈2,2,0〉 monochromator. In this design the 40 and 80 keV beams would be isolated by monochromator detuning or gold filtration, respectively. The other designs utilize fundamental radiations for both energies and would require some modification of the existing monochromator mechanism to achieve adequate tuning speed. These designs use two Si 〈2,2,0〉 crystals, one with a Bragg and the other with either a Bragg or a Laue geometry.

Rats and chicken embryos were imaged in vivo with a prototype multiple energy computed tomography (MECT) system using monochromatized X-rays from the X17 superconducting wiggler at the National Synchrotron Light Source (NSLS). The CT configuration consisted of a horizontal, low-divergence, fan-shaped beam, 70-mm wide and 0.5-mm high, and a subject rotating about a vertical axis. A linear-array high-purity Ge detector with 140 elements, each 0.5-mm wide and 6-mm thick, was used with a data acquisition system that provides a linear response over almost six orders of magnitude of detector current. The dual photon absorptiometry (DPA) algorithm was applied to images of the rat head acquired at 20 and 45 keV to obtain two new images, one representing the low-Z and the other the intermediate-Z element group. The results indicate that the contrast resolution and the quantification accuracy of the images improve stepwise; first, with the monochromatic beam and, second, with the DPA method. The system is a prototype for a clinical brain scanner. >

Monochromatic X-rays from the X17 superconducting wiggler beamline at the National Synchrotron Light Source (NSLS) were used for dual-energy quantitative computed tomography (CT) of a 27-ram-diameter phantom containing solutions of different KOH concentrations in cylindrical holes of 5-mm diameter. The CT configuration was a fixed horizontal fan-shaped beam of 1.5-mm height and 30-mm width, and a subject rotating around a vertical axis. The transmitted X-rays were detected by a linear-array Si(Li) detector with 120 elements of 0.25-mm width each. A two-crystal Bragg-Bragg fixed-exit monochromator with Si crystals was used. Dual photon absorptiometry CT data were taken at 20 and 38 keV. The reconstructed phantom images show the potential of the system for quantitative CT. >

Summary form only given. A synchrotron-based medical imaging facility has been built at the National Synchrotron Light Source. It will allow imaging of the coronary arteries using a venous instead of an arterial injection of contrast agent. Two monochromatic fan X-ray beams (at energies around the iodine K edge) are used to take sets of images. The system is described and results with five patients are presented. possible system upgrades to improve image contrast and spatial resolution and to decrease the image acquisition time have been considered. >

Measurements of the harmonic content from single‐ and double‐crystal silicon monochromators have been made in the 20‐ to 100‐keV range at the X17 superconducting wiggler beam line at the NSLS. These measurements are compared with calculations which estimate the monochromatic beam harmonic content and the detection system efficiency with good agreement. At high photon energies (≳20 keV), the scattering of x rays from an amorphous scatterer is dominated by the inelastic Compton process. At large scattering angles this will completely overwhelm the more forward directed elastic scattering. The Compton x‐ray energy shift is large enough to make the distinction between elastic and Compton scattering unambiguous when a spectrum is acquired with a solid‐state detector. This shift, which is energy dependent, allows the measurement of the relative harmonic intensity in a way that is not affected by pulse pileup in the detector and electronics. The present measurements were done to assess the level of harmonic cont...

International audience; Polyacrylonitrile (PAN) thin films electrochemically deposited on Ni have been studied by near edge x‐ray absorption fine structure, as a function of the film thickness and annealing treatment. For 20Å thick films, the polymer chains are oriented perpendicular to the surface with the C≡N groups parallel to it. Below a few angstroms, no polymerization occurs but molecules are adsorbed perpendicular to the surface. Annealing at 300°C results in the loss of the majority part of the N content of the film in contrast with the admitted mechanism for bulk PAN.

A series of niobium-vanadium alloys were investigated using the ion bombardment analytical techniques of ion scattering spectrometry, sputter induced photon spectroscopy and secondary ion mass-spectrometry. The measurements show that long term transients in signal strengths were present in all three types of analyses and that extreme care must be exercised in obtaining reproducible data. The effects of oxygen leakage on both photon and secondary ion analysis were also investigated and showed that the analysis was dependent upon the background oxygen pressure at which analysis was performed.

Five niobium-vanadium alloys, and polycrystalline niobium and vanadium, have been bombarded with 53 keV Ar + and the cluster ion yields measured. Clusters up to Nb 6 + in mass were detected. The M 2 + /M + and M 3 + /M + ratios from the pure targets agree with published values. The variation of cluster yields with concentration is in general agreement with a statistical recombination model of cluster formation, although the cluster high energy distributions do not agree with theoretical predictions.

Measurements of parameters associated with the emitted photons from a number of elements have indicated that the kinetic energies of sputtered excited atoms may be of the order of 102–103 eV. A recent result of Yu et al. [Phys. Rev. Letters 48 (1982) 427] is in contradiction to those results. We argue that the high energy values reported are the result of cascade repopulation of the upper level of the observed transition, distorting the experimental observations. Cascade corrections could reduce the energy values to the order of 10 eV, similar to the most probable energy of secondary ions.

Synchrotron radiation measurements of near-threshold and broad-range (20 eV - 3 keV) absolute photoabsorption cross sections were made at the Brookhaven National Laboratory (NSLS) and at Stanford (SSRL). Transmission data for well-characterized multilayer foils provided absolute cross sections with 10% overall uncertainties and better than 0.2% energy resolution. Several examples of our results are presented.

A reanalysis of recent inverse-photoemission data on Ni using an empirical band structure shows that the bulk band structure seen in inverse photoemission does not differ significantly from that seen in photoemission. The systematics of surface-state occurrence are in agreement with a recent phase-analysis model. The occurrence of a zone-boundary image state near Y-bar for Ni(110) is discussed. Its relatively flat dispersion curve is predicted by the phase model and is dominated by perpendicular effects rather than surface corrugation.

We have developed a method of in situ reactive glow discharge cleaning of X-ray optical surfaces which is capable of complete removal of carbon contamination [E.D. Johnson et al., Rev. Sci. Instr. 58 (1987) 1042]. Our work is the first to successfully clean an entire optical system in situ and characterize its performance at short wavelengths (as low as 10 A). The apparatus required is quite simple and can easily be fitted to most existing UHV (ultrahigh vacuum) mirror boxes or monochromators. The advantages of this technique over previously available methods include dramatic improvements in instrument performance and reductions in down time since the whole process typically takes a few days. This paper will briefly describe our results and detail the experimental considerations for application of the technique on different monochromator geometries. Possible improvements and extensions of the technique are also discussed.

Experiments are described which allow the characteristic velocity of ion neutralisation, A / a , to be measured independent of the secondary ion energy by varying the angle of ion emission and hence the velocity component perpendicular to the surface. The A / a parameter is found to be energu dependent, increasing from ≈1×10 6 cm/s at low ion energy, to ≈3.5×10 6 cm/s at 200 eV.

If the process of secondary ion formation is viewed as one in which the secondary ion is formed amongst the sputtered flux from the surface and then survives the outgoing trajectory to be analysed, we can write the yield in the energy range E to E + dE, and angle range θ to θ + dθ as $${{\rm{Y}}^ + }\left( {{\rm{E,}}\theta } \right){\rm{dEd}}\theta = {\rm{N}}\left( {{\rm{E,}}\theta } \right){{\rm{R}}^ + }\left( {{\rm{E,}}\theta } \right){\rm{P}}\left( {{\rm{E,}}\theta } \right){\rm{dEd}}\theta$$ (1) where ⇅(E,θ) is the sputtered atom flux R+(E,θ) is the probability of ionisation in the ejection process P(E,θ) is the probability of surviving the outgoing trajectory in an ionised state.

Independent measurements of the angular and energy distributions of Al+ secondary ions emitted from Ar+ bombarded aluminium are presented. The secondary ion yield is found to include an inverse exponential dependence on the emission velocity of the kind usually assumed to describe the survival probability of an ion near a surface, but the characteristic velocity, A/a, is energy dependent. With this exponential dependence removed, the ionization probability is found to be R+ α E1.1, where E is the secondary ion emission energy.