Showing papers by "Varian Associates published in 1976"

Solar cells employing stacked opposite conductivity layers

Abstract: A cell for converting received light energy to electrical energy comprises, in the simplest embodiment, four layers of differing types of semiconductive material stacked so as to form three opposite conductivity junctions. The outer two, "active", junctions are formed of confronting layers with matched lattice constants so as to provide a plurality of energy converters. The center, "connective", junction is formed by two confronting intermediate layers which have purposely mismatched lattice constants so as to provide a lattice defect site surrounding the center junction. Majority carriers (electrons and holes) will recombine at the lattice defects. This will cause the connective junction, although of apparently reverse-biased opposite conductivity type layers, to act as a low resistance ohmic connection or substantial short circuit so as to connect the energy converting portions in series. Due to the stacked arrangement of junctions in which the layers forming the active junctions have increasingly lower bandgaps toward the bottom of the stack, incident photons are converted to electrical energy with far greater efficiency than in a single-junction arrangement. Preferably the stacked layers are formed of suitably-doped epitaxially-grown layers of compounds of III-V elements (Ga, In, Al, As, P, Sb). The number of active junctions is preferably made greater than two, e.g., six is currently regarded as a practical maximum. Low resistance interconnections between the energy converting portions formed by active junctions are provided by connective junctions which are formed of lattice constant mismatched and opposite conductivity confronting layers.

Removal of spectral artifacts and utilization of spectral effects in computerized tomography

Abstract: In an instrument for reconstructing computerized tomograms utilizing penetrating radiation, typically X or gamma radiation, an apparatus and technique are disclosed for removing spectral artifacts and utilizing spectral effects to create output pictures which represent facsimilies of the distribution of molecules according to atomic number and electron density within the object being pictured. Combinations of these pictorial representations are also obtained. Reconstruction errors caused by panchromaticity in the radiation source are avoided. Attenuation within the object by means of photoelectric absorption, Compton scattering and Rayleigh scattering are isolated and analyzed separately. Techniques are disclosed for treating source beams which are arbitrarily thin or of a finite thickness. Measurements at two source spectra are performed either by means of different peak energy settings of the source, the use of a source input filter, or the utilization of detectors of different efficiencies or different response ranges, or a combination of any of the above. A statistical error analysis of the output picture is provided as a function of the statistical error in each of the two sets of measurements. A computerized fit using the least squares technique is made to establish parameters yielding analytical expressions for the various attenuation cross-sections. A calibration technique is disclosed which utilizes empirical measurements. A method for optimizing the measurement technique is disclosed. Finally, an analysis of the error in the waterbag technique is provided.

Neutron irradiation therapy machine

Abstract: In a neutron irradiation therapy machine for treating patients with a beam of high energy neutrons, a gantry is provided which supports a non-superconducting cyclotron proton accelerator and target for generating a neutron beam and which permits rotation of the accelerator and neutron beam around an axis of revolution coaxial with a patient treatment zone. A counter-weight is carried from the gantry in a diametrically opposed relation to the cyclotron and behind the support bearing for counter-weighting the cyclotron and its associated equipment rotationally and longitudinally. The cyclotron includes an enclosing magnetic return yoke having a re-entrant portion in axial alignment with the magnetic poles of the cyclotron for reducing the weight of the yoke. The enclosing magnetic return yoke, and any additional surrounding material such as boron loaded polyethylene and lead, provide radiation shielding to protect the patient. An alternative patient table is coaxially mounted of the gantry and supported from a rotor portion thereof via a bearing assembly so that the rotor rotates around the stationary patient table. A neutron beam stopper is carried from the rotator of the gantry in axial alignment with the neutron beam and diametrically opposed to the cyclotron for absorbing neutrons passing through the patient treatment zone. Evacuable radio frequency transmission lines are provided for feeding RF power to the cyclotron and which pass through the yoke and are connected in gas communication with a vacuum pump for evacuating the cyclotron via the intermediary of the RF transmission lines. The cyclotron accelerates a beam of charge particles, such as protons, to relatively high energy, as of 30 MeV, to bombard a target formed of first and second materials. The first target material has a relatively high yield for high energy neutrons at proton energies in excess of 15 MeV, whereas a second portion of the target has a low yield for neutrons at proton energies less than 15 MeV, for stopping the protons. Tungsten shielding elements are disposed surrounding the neutron producing target and other regions for attenuation of neutrons falling outside of the desired neutron beam lobe. An adjustable and rotatable neutron beam collimator is arranged for varying the orientation and cross sectional dimensions of the neutron beam as applied to the patient treatment zone.

Deformation field of a misfitting inclusion

Abstract: J.D. Eshelby (1957, 1959) has calculated the deformation field associated with an ellipsoidal inclusion in a state of homogeneous strain within an infinite matrix. Since most real precipitates occur with facets, the strain within such an inclusion is not uniform. Thus, plate precipitates of θ ′ in Al-Cu and η in Al-Au have coherent broad faces with mismatches of 1.34 and 4.95 % respect- ively and semicoherent or disordered interfaces at the edges with residual mismatches of about −4.3 and −1.00% normal to the broad faces. The deformation field in the matrix around such precipitates has been calculated using Kelvin's (1848) result for the stress field due to a point force. The calculations show the existence of high stresses near the edges of the precipitates where they have an appreciable misfit. Unlike the case of an ellipsoidal inclusion, the stress fields of these precipitates have dilatational components which can affect the diffusion of solute atoms to them and, thus, the kinetics of interface migration. The behavior of alloys containing these precipitates indicates that the moduli of the precipitates are somewhat greater than those of the matrices. The present calculations, based on the assumption that the two moduli are the same, underestimate the actual deformation field in the matrix. In real systems, therefore, the effects of the deformation field on misfit dislocation nucleation and kinetics of interface migration are likely to be somewhat greater in general.

High speed fet employing ternary and quarternary iii-v active layers

Abstract: A field effect transistor (FET) preferably employs an epitaxial layer of indium gallium arsenide as its active layer. On the surface of the active layer, ohmic source and drain contacts are spaced from respectively opposite sides of a Schottky barrier (rectifying) gate electrode. The active layer is grown over an epitaxial transition layer which is graded from gallium arsenide to indium gallium arsenide and is doped with chromium or oxygen to be semi-insulating. The transition layer is in turn formed over a bulk, intrinsic layer of gallium arsenide. High speed operation of the FET is obtainable because the active layer has excellent electron transport characteristics. Other materials suitable for the active layer are indium arsenide phosphide and indium gallium arsenide phosphide.

Tomographic scanning apparatus having detector signal digitizing means mounted to rotate with detectors

Abstract: Scanning apparatus is disclosed for use in computerized axial tomography systems. The apparatus includes an assembly rotatable about an axis extending along a central opening defined therein, and means for positioning the body portion to be examined within the central opening so that the axis of assembly rotation is perpendicular to a plane passing through the bodily structures to be examined. A source of penetrating radiation is mounted on the assembly toward one side thereof and provides radiation in the form of a fan beam. Detector means for the radiation are positioned on the assembly opposite the source, enabling detection of radiation which traverses laterally and is not absorbed in the thin body section in which the aforementioned plane resides. Means are provided for rotating the assembly so that the fan beam impinges upon said body portion at a plurality of incident directions. Signal processing and conditioning means mounted on the assembly and movable therewith, receive the output signals from the detector means and amplify and convert same to digital form. Slip ring interconnection means rotatable with the assembly, receive the outputs from the signal processors and conditioners and interfeed these signals to a computerized image reconstruction station. Slip rings rotatable with the assembly also provide interconnection enabling power and control inputs to the radiation source and to other portions of the apparatus. The assembly is continuously rotatable through successive 360 degree rotations and the examination sequence may be initiated at any point in the rotation of the assembly. The detector comprises an array of elements and means are provided for adjusting the gains of each channel associated with the individual detector elements as an incident of the examination process, thereby enabling compensation for drift in the channels.

Fluid containment structure for transducer system

Abstract: Pressure transducer apparatus primarily for medical use in determining the hemodynamic pressure associated with circulation of the blood. The pressure transducing wall is in contact with a highly compliant diaphragm wall of a fluid container adapted for connection to a patient's blood system. In order to prevent distortion in the blood pressure wave as it is transmitted through the container diaphragm wall to the transducing wall, means are provided for venting air trapped between the diaphragm and the transducing wall.

NMR Spectrometer employing self centering turbine

Abstract: A gyromagnetic resonance spectrometer employing a spinning sample in a magnetic field, the spinning sample being affixed to a gas driven turbine which is supported by a gas bearing. Means are provided for firmly holding and centering the sample at more than one axial position thereby aligning the sample tube with the turbine axis irrespective of variations in sample tube diameter and straightness.

High performance liquid chromatography system

Abstract: PATENT APPLICATION OF of MINER N. MUNK, KENNETH C. JUDAH, PIERRE Y. ACHENER and DETLEF R. BOEHME for HIGH PERFORMANCE LIQUID CHROMATOGRAPHY SYSTEM ABSTRACT OF DISCLOSURE A liquid chromatography system, including a reservoir for a liquid mobile phase, a liquid chromatography column, reciprocating pumping means for pumping the mobile phase through the column, and motor means for driving the pumping means through successive reciprocation cycles. Means are provided for controlling the rotational speed of the motor throughout the reciprocation cycle of the pump, so as to provide preselected average rotational speeds over predetermined subintervals of each successive reciprocation cycle. Application of the control cycle is synchronized with the pump cycle so that the said speed control is properly applied over each successive reciprocation cycle.

Variable energy highly efficient linear accelerator

Abstract: An accelerator for a linear beam of charged particles has a first accelerating section upstream which modulates and accelerates the dc beam. This section is a traveling-wave circuit through which the entire rf power flows from the driving source. Output power from the other end of the traveling-wave section flows through a transmission line to a standing wave accelerating section downstream of the input section. An attenuator and a phase shifter between the two sections allow adjustment in the energy added to the particles in the downstream standing-wave section without disturbing the synchronism of the beam with the upstream accelerating section. As a result a high efficiency of acceleration and narrow energy spread of the final accelerated beam are achieved over a wide range of particle energies.

Gyromagnetic resonance spectroscopy employing spin echo spin-spin decoupling and two-dimensional spreading

Abstract: A method of gyromagnetic resonance spectroscopy is disclosed which simplifies the resultant spectra by eliminating spin-spin coupling effects. The method is particularly useful for eliminating homonuclear spin-spin coupling effects. In the method, spin echo resonance of the resonators is obtained and the time elapsing between tipping of the resonators and detection of the resultant echo t 1 is changed from one measurement to the next. The resultant echos are measured at equal intervals of time t 2 . Echo resonance data is Fourier transformed from the time domain into the frequency domain to obtain spectral data in the frequency domain as a function of t 1 . A second Fourier transform of the resonance data is then effected to transform the spectral data into data which is a function of both ω 1 and ω 2 where ω 1 and ω 2 are each related to 1/t 1 and 1/t 2 , respectively. The spectral data in the ω 1 -ω 2 plane is then projected at 45° to the ω 2 and ω 1 axes to derive spectral data free of spin-spin coupling effects. The data may also be projected perpendicular to and onto the ω 1 axis to obtain a J coupling spectrum.

Convergent light illuminated flow cell for liquid chromatography

Abstract: Single and dual beam flow cells for liquid chromatography that provide good detectability and linear response with small sample volumes. A cylindrical window surrounds the sample flow path to permit focusing convergent light rays through the center of the flow path and along optical paths of equal length through the cell. Optical stops limit the light passing through the cell to convergent rays incident to the window surface. A wide acceptance angle for the rays results in high light transmission and averages variations in light output along the light source. A dual beam flow cell utilizes a common exit for the sample and reference liquids. The flow cells are economically constructed for direct coupling to a chromatographic column by using a standard compression fitting union and can be used in a single wavelength or discrete wavelength detector, or in a spectrophotometer.

Broadband microwave bias network

Abstract: For supplying a bias (modulation) signal, either AC or DC, to a microwave circuit, a network consisting of a low pass filter is provided which presents a high isolating impedance to an extremely wide bandwidth of microwave frequencies, while allowing low frequency bias or modulating signals to be supplied to the microwave circuit without significant attenuation. The network consists of two helical inductors, one within the other, plus a bypass capacitor. The inner small inductor presents a high, non-resonant impedance to high microwave frequencies and the outer, larger inductor presents a high impedance to lower microwave frequencies. The bypass capacitor cooperates with the outer inductor to complete the filter circuit for the lower microwave frequencies. The smaller inductor's proximity to and within the larger inductor provides a distributed shunt capacitance to ground so as to terminate the filter for the higher microwave frequencies at the smaller inductor.

Method and apparatus for reducing the transient effects of liquid compressibility in a liquid chromatography system

Abstract: Method and apparatus for damping oscillatory behavior and reducing the effective time constant incident to reattainment of equilibrium pressure and flow following a change in fluid pressure or flow rate in a liquid chromatography system. The system may include a chromatographic column, a reservoir for a slightly compressible liquid mobile phase, and piston means cooperating with the reservoir and normally driven at a velocity which is constant over a given time interval, for enabling pumping of the mobile liquid phase through the chromatographic column. In accordance with the invention, a transient velocity component is superimposed upon the constant velocity component of the mobile liquid phase caused by the piston motion. The transient velocity component is proportional to the reservoir volume and to the time derivative of pressure in the reservoir. The additionally imparted motion damps the transient oscillations that arise from any pressure change imposed on the slightly compressible liquid phase. Such pressure changes may e.g., be induced during operation of the chromatography system in a gradient elution mode.

Analytical instrument optimum data acquisition method and apparatus

Abstract: An analytical instrument employing ensemble averaging to improve the signal-to-noise ratio including means for determining the most efficient scaling factor and for controlling the instrument to maintain assurance of efficient averaging.

Pulsed RF excited spectrometer having improved pulse width control

Abstract: RF excitation for a spectrometer is obtained by pulse width modulating an RF carrier to produce the desired broadband RF exciting spectrum. The RF excitation includes a train of composite RF pulses, each composite pulse having a primary pulse portion of a first RF phase and a second pulse portion of a second RF phase opposite that of the first. In this manner, the finite rise and fall times of the primary pulse portion are compensated for by the corresponding rise and fall times of the secondary pulse portion. The primary pulse portion is lengthened by an amount equal to the secondary pulse portion so that the secondary pulse portion cancels the added primary pulse portion. In a spectrometer the compensating second pulse component removes certain undesired side bands of the RF excitation caused by the finite rise and fall times of the applied RF pulses. The compensating second pulse component removes certain undesired side bands associated with each of the resonant lines of the excited resonance spectrum, thereby simplifying the resonance spectrum of the sample under analysis, particularly for wide band RF excitation.

Electron beam evaporator having beam spot control

Abstract: An electron beam evaporator employs an electron gun which projects a beam of electrons over an arcuate beam path to a crucible target for heating and evaporating the target material in use. The electron beam passes through the magnetic field supplied by a pair of pole pieces of a beam focus magnet which produces a main field transverse to the direction of the electrons to cause the beam to take the arcuate trajectory. Two pairs of auxiliary pole pieces project inwardly of the main pole pieces to provide a pair of beam focus lenses. One of the magnetic lenses is disposed on the inside of the beam path, whereas the other is disposed on the outside of the beam path to provide beam lateral focusing and defocusing lenses, respectively. The lenses are adjustable, preferably electromagnetically for controlling the beam spot size on the target crucible so that the evaporation characteristics can be optimized for a given beam power. In addition, the magnetic lenses are adjustable, preferably electromagnetically, for sweeping the position of the beam spot longitudinally and/or laterally of the crucible target.

Assymetric cylinder electron capture detector

Abstract: An asymmetric cylinder electron capture detector comprises an electrode configured to define an ionization volume, a source of ionizing radiation disposed within the ionization volume, a collector electrode, with a gas flowing past the collector electrode into the ionization volume. The electron current to the collector electrode provides an indication of the presence of electronegative constituents in the gas passing into the ionization volume. In order to provide wide dynamic range, the face of the collector electrode is disposed as close as possible to the electrode defining the ionization volume, yet is located so as to minimize field-free background current. The collector electrode and the electrode defining the ionization volume are each of cylindrical configuration, and are coaxially aligned but are spaced apart with respect to each other. The two electrodes are mechanically connected via an intermediately disposed cylindrical insulator cylinder. The collector electrode is received in one end of the insulator cylinder, and the electrode defining the ionization volume is received within the other end of the insulator cylinder. The collector electrode has an elongate portion extending into the interior of the insulator cylinder, but spaced apart from the inner surface of the insulator cylinder. This configuration provides a long insulative path to prevent electrical leakage between the electrodes. A transverse gas exit port is provided in that portion of the collector electrode within the insulator cylinder in order to impart turbulence to the flow of gas through the insulator cylinder into the ionization volume.

Flame ionization detector with flame monitor

Abstract: A flame ionization detector including means for monitoring the flame condition, so as to enable ignition of an extinguished flame. An igniter coil is mounted proximate the burner nozzle of the FID, and thermocouple means are provided including a hot junction in thermal contact with the nozzle, and a spaced cold junction. Means are provided for applying an electrical potential to the igniter coil to enable ignition of the flame upon a flame-out condition being detected as measured by the thermocouple output. In a preferable embodiment, the ends of the igniter coil are connected to a pair of electrical leads, with the connection zones defining the hot and cold junctions of the thermocouple. This permits the same lead pair to provide both the potential enabling the igniter function of the coil, and the interconnection for the thermocouple output signal. The same lead pair may also be utilized to provide the biasing potential to the burner nozzle.

Circuit for linearizing the response of an electron capture detector

Abstract: A circuit improvement is disclosed for use in an electron capture detector of the type including an electron capture cell, means for applying polarization pulses to the cell to derive a cell current, means for varying the pulse rate to maintain the cell current constant, and means for converting the pulse frequency to an analog signal indicative of the concentration of an electron-capturing component. Pursuant to the improvement, the pulse rate is varied by means which include an electrometer-amplifier for receiving the cell current and providing an output indicative of cell current departure from a reference current; an integrator for receiving the electrometer-amplifier output, the integrator generating a saw-tooth wave form, the slope of which is proportional to the magnitude of the electrometer-amplifier output signal; means for comparing the integrator output signal with a fixed reference voltage and for generating a triggering pulse when the two are equal; and pulse generator means coupled to the comparator output for generating the polarization pulses in response to the triggering pulses.

Noise And Dose In Energy Dependent Computerized Tomography

Abstract: We previously described techniques for extracting complete energy dependent information from simple measurements. In this paper we discuss the noise properties of this technique.

Keying waveform generator for spectrophotometer

Abstract: In a double beam spectrophotometer employing a rotating optical chopper to direct a beam of electromagnetic radiation alternately through sample and reference channels to a photomultiplier tube, a beam interrupter is used in combination with a photodiode and a photocell to generate a square wave signal having a predetermined temporal relation to the rotation of the optical chopper. The square wave signal is integrated to provide a triangular waveform, whose maxima and minima correspond, respectively, to the passage of the beam through one or the other of the sample and reference channels, and whose cross-over points with respect to a zero reference level correspond to dark intervals during which the beam is blocked from entering either channel. Keying circuitry responsive to the cross-over points provides for detection of dark current generated by the photomultiplier tube, while keying circuitry responsive to the maxima and minima synchronizes analysis circuitry associated with the sample and reference channels with the passing of the beam therethrough and provides for correction of the output of the photomultiplier tube to compensate for dark current.

Magnetron slot mode absorber

Abstract: In a coaxial magnetron the resonant circuit interacting with the electrons is coupled to a stabilizing resonator operating in a mode with circular electric field. The coupling is thru a set of slots in the intervening wall. Undesirable resonances localized in the slots are damped by lossy material at the ends of the slots. Undesirable damping of the cavity mode is prevented by a conducting shield covering exposed area of the lossy material and spaced into the cavity away from the slots.

Dual mode gridded gun

Abstract: Travelling wave tubes designed to operate interchangeably at low power cw and high pulsed power have grids to gate the pulses and to switch the peak beam current between two values. To preserve optimum beam-focus conditions, the beam diameter should be simultaneously switched. A grid covering the central region of a concave cathode draws the low-current, small beam for cw operation or the central part of a large pulsed beam. A second grid controls added pulsed emission from the surrounding annular region of te cathode. To provide the proper ratio of beam sizes and uniform cathode loading, the cathode has radially varying radius of curvature. A hyperboloid of revolution is a good shape.