Showing papers by "Varian Associates published in 1997"

Radiotherapy couch top

Abstract: A radiotherapy couch top has a frame and preferably a pair of beams extending parallel to each other, capable independently of moving towards or away from each other while keeping their mutually parallel longitudinal direction. For supporting the beams in this way, at least two linear slide bearing ways are provided, extending parallel to each other in a transverse direction perpendicular to the beams, at least one of them being supported by the frame. A pair of riding blocks are on each of these linear slide bearing ways, each supporting a corresponding one of the beams and slidable along the linear slide bearing way. Panels are placed over the beams, including one attached to the frame and another which is removable. The removable panel may be replaced with another having an open window section provided with a grid of carbon fiber stringing capable of supporting the patient and allowing projection of radiation directly onto the patient's skin.

Inductively coupled plasma reactor with faraday-sputter shield

Abstract: A slotted Faraday-sputter shield is formed to provide no line-of-sight paths therethrough. The Faraday-sputter shield is preferably finished on its outer surface with a smooth highly electrically conductive finish, and on its inner surface with a rough surface to aid in adhering material deposited during plasma processing. The shield may be arranged in an inductively coupled plasma reactor having an RF powered coil disposed external to a plasma chamber, a plasma powered by the coil to be formed within the dielectric chamber, the shield being disposed within the chamber between the plasma and the RF coil to provide no line-of-sight paths between the plasma and the RF coil while permitting inductive but no capacitive coupling between the RF coil and the plasma.

Mass spectrometer system and method for transporting and analyzing ions

Abstract: A mass spectrometer system for performing a separation of ions from neutrals and mass analyzing ions comprising an ion generating source with an ion introduction system, a radio-frequency ion guide and a mass analyzer disposed within a vacuum chamber. The radio-frequency ion guide is positioned with respect to the ion introduction system so that a main axis of the radio-frequency ion guide is angled toward a central axis of the ion introduction system. The trajectory of the ions is diverted toward the main axis of the radio-frequency ion guide while neutrals continue their flow along the central axis. The ions from the ion introduction system are transported via the radio-frequency ion guide to the mass analyzer.

Theory of the quadrature elliptic birdcage coil.

Abstract: This paper presents the theory of the quadrature birdcage coil wound on an elliptic cylindrical former. A conformal transformation of the ellipse to a circular geometry is used to derive the optimal sampling of the continuous surface current distribution to produce uniform magnetic fields within an elliptic cylinder. The analysis is rigorous for ellipses of any aspect ratio and shows how to produce quadrature operation of the elliptic birdcage with a conventional hybrid combiner. Insight gained from the transformation is also used to analyze field homogeneity, find the optimal RF shield shape, and specify component values to produce the correct current distribution in practice. Measurements and images from a 16-leg elliptic birdcage coil at both low and high frequencies show good quadrature performance, homogeneity, and sensitivity.

X-ray target having high z particles imbedded in a matrix

Abstract: A rotating anode X-ray target has a matrix structure such as a carbon-carbon matrix and a high Z material imbedded inside this matrix structure. The high Z material may be a refractory metal with atomic number at least 72, its alloy or carbide and may be imbedded in the matrix either as discrete particles or as a non-discrete layer. Such a target can be made by any of a number of known methods such as chemical vapor deposition and chemical vapor infiltration. Without a TZM layer or a braze required for holding together an X-ray-producing surface layer and a carbon heat storage material, the target can be made lighter and can be operated at higher temperatures.

Decoupling: theory and practice. I. Current methods and recent concepts.

Abstract: Current methods for broadband heteronuclear decoupling are reviewed from a historical perspective. The principal concern is that decoupling should be effective over a wide range of chemical shifts without undue radiofrequency heating of the sample, particularly when human patients are involved. Continuous-wave methods are the least efficient in this respect, followed by noise decoupling. Composite pulse schemes offer a more effective use of radiofrequency power, while adiabatic passage methods are the most efficient of all. Bi-level decoupling employs a low level of radiofrequency irradiation during the relaxation delay to maintain the nuclear Overhauser effect, with a higher level during signal acquisition in order to decouple over a wide frequency band. All decoupling sequences introduce cycling sidebands into the observed spectrum, and schemes are described to minimize the intensity of these artifacts. In part II, practical applications of decoupling methods are examined in the context of in vivo spectroscopy, where the improvements in sensitivity and resolution through broadband decoupling can be critical for solving clinical problems. Attention is focused on the regulatory limits on power deposition in these experiments. A tabulation of the existing work on decoupling in biological tissue is presented, mainly involving 31 P and 13 C spectroscopy in vivo or in vitro.

Characterization of an amorphous-silicon fluoroscopic imager

Abstract: This paper describes a dual-mode, flat panel imaging system capable of both fluoroscopy and radiography. Two generations of large area sensing technology are described. The general system architecture incorporates both the high sensitivity and data throughput required for fluoroscopy with the large signal capacity, spatial resolution and form factor necessary for radiography.

Method for trapping ions into ion traps and ion trap mass spectrometer system thereof

Abstract: A method and mass spectrometer system for trapping ions within an ion trap by increasing the flight path of ions therein. An ion beam is produced by external ion source and is directed to the ion trap which comprises at least one trapping electrode in proximity to an exit region of the ion beam from the ion trap. A retarding DC voltage is applied to the trapping electrode during ion accumulation time for creating a fringing reflection field and for retaining ions within the ion trap.

Electron beam superimposition method and apparatus

Abstract: A method and apparatus for superimposing a plurality of electron beams at a desired location after X-ray tube manufacturing processes are generally complete. The method is embodied in providing mechanical and electrical means which are internal to the X-ray tube which provide means for adjustment of a focal point of a plurality of electron beams being emitted from a cathode assembly to thereby provide precise control of where the plurality of electron beams achieve superimposition on a target anode.

Real-time gas-chromatography mass-spectrometry trace vapor detection

Abstract: A gas flow distribution system accumulates a sample from a sample bearing carrier gas in a micro-accumulator, delivers it using a carrier gas to a gas chromatography column, and supplies a carrier gas to the gas chromatography column to facilitate separation of the sample into sample components and transport the sample components to a mass spectrometer for trace vapor detection and analysis or testing in real time. The system is made of inert components and configured to have low dead volume for improved performance and accuracy of detection. External valves are employed for easy management and balance of the flow in the system to minimize operation time and facilitate continuous accumulation, delivery, and testing of the sample. The delivery of the sample to the gas chromatography column using an electrically heated cold trap as the micro-accumulator can be performed extremely fast. By further combining the sample accumulation phase and the sample testing phase, real time operation of trace vapor detection is achieved. Because the step of delivering the sample to the gas chromatography column is performed quickly, the accumulation of the sample can resume quickly and is nearly continuous for improved efficiency.

Use of titanium hydride in integrated circuit fabrication

Abstract: A process for forming titanium silicide layers on semiconductor device silicon regions which have native oxide thereon utilizes a reactively sputter deposited layer of TiHx≤2 followed by a rapid thermal anneal in a nitrogen bearing gas. The same process produces a titanium nitride/titanium silicide bilayer on silicon, and a titanium nitride/titanium bilayer on silicon dioxide.

Rotating sealing device

Abstract: A rotating sealing device for sealing between a wall separating two mediums under substantially different pressure and a rotatable shaft utilizes a combination of a liquid metal seal comprising at least one liquid metal ring and a shield means which prevents contamination of the metal ring by gases coming into contact with the liquid metal. Magnetic fluid seal, a ring of an oil material, or inert gas may be used as a shield to protect the liquid metal.

Sample delivery system used in chemical analysis methods which employs pressurized gas for sample conveyance

Abstract: A sample delivery system for a flow-through NMR analysis is provided, which utilizes pressurized gas as a means for conveying a sample into and out of an NMR spectrometer. Two sources of gas pressure, a forward pressure and back pressure, oppose the sample within the tubing of the sample delivery system and the tubing of the flow-through system which are operatively coupled together. Conveyance of the sample in any direction within the tubing is achieved by adjusting the pressure differential. Precise positioning of the sample in the magnetic field center and complete removal of the sample from the NMR spectrometer when analysis is complete are achieved by using a signal processor which receives signals from the NMR detector or other detectors positioned along the length of the tubing. These signals provide an indication of the position of the sample in the tubing. The signal processor uses this information to adjust the forward and back pressure, thereby achieving the desired positioning of the sample.

Cooling device for cooling heatable gas chromatography analyte sample injector

Abstract: The present invention is an improved modular cooling device for cooling gas chromatography analyte sample injectors. The invention is embodied in a series of tubes connected in fluid communication from a coolant supply valve to the injector heating block. A flexible supply tube capable of carrying coolant while maintaining structural integrity at temperatures up to about 150° C., and having a low thermal conductivity is connected in fluid connection with a coolant supply at one end, and a transition tube at the other. A transition tube, in fluid communication with the supply tube at one end and with the cooling tube at the other, is selected to maintain structural integrity at temperatures up to 450° C. and to have a low thermal conductivity. The cooling tube is in fluid communication with the transition tube at a receiving end and with an exhaust at an exhaust end, and has an outer surface that is physically engageable with a surface of the heating block. The cooling tube is capable of maintaining structural integrity at temperatures up to 450° and has a high thermal conductivity (at least about 200 watts/meter ° C.) to facilitate heat transfer. The cooling tube further has a flattened surface for creating a greater surface area for physical engagement with the heating block to provide greater cooling effect.

Current mode analog signal multiplexor

Abstract: A current mode analog signal multiplexor includes multiple input multiplexed differential amplifiers (12, 14), a reference amplifier ( 12.0, 14.0) and an output differential current amplifier (18, 20). An input multiplex control signal selects and enables one of the input multiplexed differential amplifiers for buffering and steering the input signal current to one side of the output differential current amplifier. The reference amplifier drives the other side of the output differential current amplifier. The output node of the output differential current amplifier remains at a substantially constant voltage potential while providing an output current which varies in relation to the selected input signal.

Boron doping of silicon by plasma source ion implantation

Abstract: We have performed an extensive analysis of the structural and electrical characteristics of 150 and 200 mm Si wafers boron doped by low-energy (−0.5 to −5 kV) plasma source ion implantation (PSII) from a BF 3 plasma and subsequent rapid thermal annealing. The formation of shallow junctions (60 nm or less) required for 0.18 μm device geometries has been verified by secondary ion mass spectrometry measurements and electrical characterization. Rutherford backscattering spectrometry and high resolution electron microscopy analyses have shown a thin (≤5 nm) amorphous region in the as-implanted silicon; no evidence of dislocations or other extended defects has been observed. After annealing, the implanted silicon appears to be perfectly crystalline. Good doping uniformity across a wafer and good wafer-to-wafer repeatability have been observed in the PSII process. Excellent device characteristics (threshold voltage rolloffs, junction leakage, etc.) have been obtained from MOSFET structures fabricated using this doping technology. All results suggest that boron doping of silicon by PSII results in materials and device characteristics that are suitable for advanced device fabrication.

Nonlinear electrodynamics in cuprate superconductors

Abstract: We present two types of experiments which probe the high-frequency conductivity of BSCCO films in the presence of large superfluid velocities. In the first the superflow is the static velocity field associated with the vortex lattice. In the second the velocity is dynamic, induced by high-intensity single-cycle electromagnetic pulses. We show that intrinsic pair-breaking in a d -wave superconductor can provide a unified explanation for both effects.

Ergonomics Program Development: Prevention in the Workplace

Abstract: An ergonomics program is discussed in which prevention of work-related repetitive strain injuries is the primary focus. The hazard assessment component of the program consists of review of injury/illness records by department and location, work site surveys with risk factor observation, and a survey of workers for evidence of risk-related tasks and recommendations for correctives. Tasks are prioritized according to degree of hazard, and alternative interventions are developed for each task. Elements of interventions can include a corrective action team; an ergonomic specialist team; training; exercises; and equipment, process, design, and engineering changes. This approach has resulted in a significant reduction in repetitive strain injury severity.

Filamentation in high-power tapered semiconductor amplifiers

Abstract: Filament formation is currently a limiting factor in the development of high power, spatially coherent semiconductor amplifiers. An experimental and theoretical investigation has been conducted to examine the filamentation tendencies of tapered amplifier structures. Experimental measurements of the far-field intensity distribution of a tapered amplifier which has been intentionally `seeded' to filament are compared to a perturbative solution of the paraxial wave equation. This model is used to address several design issues which can be optimized to suppress filamentation. The effect of non-uniform carrier injection due to carrier- induced bandgap changes is also investigated numerically.

Low temperature and low cost planarised aluminium interconnect for sub-half micrometre VLSI circuits

Abstract: Planarised Al interconnect structures for sub-half micrometre integrated circuits have been fabricated by a novel low temperature and low pressure sputtering deposition technique. Simultaneous high aspect ratio interconnect hole fill and metal layer planarisation were achieved with moderate heat applied to processed wafers during the Al deposition. Low via resistance (~1 Ω for 0.35 µm vias) and high via chain yield (~100%) have been obtained on the wafers processed at a wafer temperature of 380°C.

Liquid ion chamber electrode apparatus

Abstract: The present invention provides electrode assemblies for LIC imagers that maximize ion collection and the electric field for the minimum bias voltage. To achieve this optimization the ion collection is confined to small regions. Due to this limited ion collection region, high neutralization efficiencies and fast sweep-out times can be obtained. Furthermore, with an electrode separation of approximately 0.1 millimeters, pulse voltages of less than 100 volts can be used. Low voltages result in improved reliability, longer system life, and lower safety risks.

Accessory clamping system for couch top

Abstract: An accessory has a fixed member and a rotatably supported and eccentrically mounted disk which are each inserted into a corresponding one of a pair of crescent-shaped indentations formed on a panel. As the disk is rotated, its center moves towards the fixed member, causing the disk to press against the inner wall of the indentation and locking the accessory to the panel securely.

Vapor jet vacuum pump and method of manufacture

Abstract: A vapor jet vacuum pump includes a pump housing, a boiler sealed to the pump housing and a jet assembly mounted within the pump housing. The pump housing is a low porosity metal casting and has an inlet and a foreline. The boiler includes a boiler housing defining a reservoir for a liquid, and a heater for vaporizing the liquid to form a vapor. The jet assembly directs a vapor jet toward the housing. In a preferred embodiment, the boiler housing is a low porosity metal casting. A method for making the pump housing includes the steps of casting two or more low porosity housing blanks, machining the housing blanks to provide finished housing elements and attaching the finished housing elements together to form the pump housing.

Spontaneous-emission measurements in broad-area quantum well semiconductor lasers

Abstract: Spontaneous emission spectra have ben obtained from semiconductor quantum well lasers of varying epitaxial design. Initial measurements taken normal to the active region through the substrate and a transparent contact exhibited a modulated spectral profile dependent on the collection angle. An image model with the quantum well active region as the source and the p-side metallization as the image plane explains the observed modification and as such, presents an excellent example of a simple cavity quantum electrodynamics (QED) effect in a planar semiconductor laser. The phenomenon is made possible by the proximity of the quantum well active region to the p-side electrical contact of the device. Modification of the spontaneous emission rate and spectra can be substantial and must be accounted for if one hopes to correctly infer modal gain or carrier heating phenomena in a device using this geometry. Alternatively, to avoid the influence of the cavity QED effect, spontaneous emission can be obtained through the side wall of the device. Using this method for collection of spontaneous emission, the effect of quantum well dimensions on carrier heating in single quantum well InGaAs or GaAs active regions was also investigated. Incomplete pinning of the carrier density was observed above threshold in these samples with low duty cycle pumping.However, minimal distortion of the carrier distribution to higher energies was observed at room temperature up to current densities of 1.6 kA cm-2. Low temperature spontaneous emission spectra revealed gain suppression from carrier heating and possibly spectral hole burning in InGaAs deep and shallow quantum well lasers.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.