Showing papers in "Review of Scientific Instruments in 1964"
TL;DR: Five simple microwave cavities for producing discharges in gases were tested in He and H2 at pressures from 1 μ to 1 atm and one of the newly designed models offered a considerable improvement over early models with respect to compactness, ease of attachment to the system, and efficiency.
Abstract: Five simple microwave cavities for producing discharges in gases were tested in He and H2 at pressures from 1 μ to 1 atm. Three of the cavities are commonly used, and two have been recently designed. One of the newly designed cavities offered a considerable improvement over early models with respect to compactness, ease of attachment to the system, and efficiency.
418 citations
TL;DR: In this paper, the authors describe a complete pulsed nuclear resonance spectrometer suitable for experiments in solids, which can operate at any frequency between 2 and 30 Mc, an rf pulse output power of 5 kW over most of this range, a receiving system recovery time of 5-10 μsec at 10 Mc, a sensitivity usually limited by thermal noise in the receiver coil, use of phase coherent detection, the availability of a wide variety of pulse sequences, and good long and short term stability of the entire system.
Abstract: The description of a complete pulsed nuclear resonance spectrometer suitable for experiments in solids is given. Its major features are the ability to operate at any frequency between 2 and 30 Mc, an rf pulse output power of 5 kW over most of this range, a receiving system recovery time of 5–10 μsec at 10 Mc, a sensitivity usually limited by thermal noise in the receiver coil, use of phase coherent detection, the availability of a wide variety of pulse sequences, and good long and short term stability of the entire system. Brief instructions for operating the apparatus are included. A method of using the ``boxcar'' integrator to record directly the steady‐state absorption (χ″) or dispersion (χ′) is explained.
215 citations
TL;DR: In this paper, a method for the production of uniform-sized liquid droplets is proposed, which is based on the principle that a cylinder of liquid is dynamically unstable under the action of surface tension.
Abstract: A method useful in the production of streams of uniform‐sized liquid droplets, which are uniformly spaced relative to one another, is discussed. An extension of the method which is useful for the production of single droplets of known size is also given. The method is based on the principle that a cylinder of liquid is dynamically unstable under the action of surface tension. A capillary wave is launched onto a cylinder of liquid or jet which selects a particular mode of instability. The process of the disintegration of the jet is thereby regularized to the extent that extremely uniform droplets result. The size of the droplets is controlled by the inside diameter of the capillary tube through which the liquid flows, and therefore, the size can be varied over wide limits. By charging individual droplets and using electrostatic means to deflect them out of the stream, individual droplets can be isolated.
176 citations
TL;DR: In this paper, an electron spectrograph consisting of an electron source, an electron monochromator, a gas cell, and an electron energy analyzer is described, and it is shown that space charge within the beam requires operation of the energy selectors at the lowest possible energy if high current, together with high resolution is required.
Abstract: An electron spectrograph consisting of an electron source, an electron monochromator, a gas cell, and an electron energy analyzer is described. The electron energy spread from the monochromator as seen by the analyzer is 0.005 eV at 3.35 eV primary energy. It is shown that space charge within the beam requires operation of the energy selectors at the lowest possible energy if high current, together with high resolution, is required.
145 citations
TL;DR: In this paper, the authors present the result of calculations on ion deflection and focusing in magnets that have realistic, extended fringing field rather than sharply cutoff fringing fields, and show that the most important effects of the change from sharp cutoff to extended fringes fields are (a) displacements of the beam center line at entrance and exit (a ''zeroth-order'' effect), and (b) reduction of first-order z-direction (''vertical'') focusing.
Abstract: This paper presents the result of calculations on ion deflection and focusing in magnets that have realistic, extended fringing fields rather than sharply cutoff fringing fields. The most important effects of the change from sharp cutoff to extended fringing fields are (a) displacements of the beam center line at entrance and exit (a ``zeroth‐order'' effect), and (b) reduction of first‐order z‐direction (``vertical'') focusing. When the pole boundaries are curved or an effective curvature is caused by the proximity of pole‐piece corners, there are further first‐order effects on the trajectories. These effects can be minimized, and in practice made negligible, by correct centering of the beam relative to the pole‐piece corners at entrance and exit.
123 citations
TL;DR: In this article, a small sphere is placed without bonding on a shear mode transducer and the transducers are driven with a pulse at one of the resonant frequencies and the free decay of the sphere's vibrations is observed by switching the transducers to a receiver.
Abstract: A technique has been devised whereby the elastic and anelastic properties of solids can be measured both as a function of frequency and temperature. A small sphere, of the order of a few millimeters in diameter, is placed without bonding on a shear mode transducer. The transducer is driven with a pulse at one of the sphere's resonant frequencies and the free decay of the sphere's vibrations is observed by switching the transducer to a receiver. From the decay of the vibrations, the internal frictionQ −1 may be calculated. Various modes may be excited and from comparison with the computed mode spectra of an isotropic solid, the Lame constants, λ and μ, and Poisson's ratio may be calculated directly. Measurements have been made over a range of temperatures from 1.4 to near 400°K, the present upper limit being set by the solder connections to the transducer. Several materials have been tested and the results for two single‐crystal nonmagnetic garnet spheres are given as representative of the capabilities of the technique for reasonably isotropic substances. The values of Q −1 for these garnets lie between 3×10−7 and 2×10−5 at a frequency of approximately 2 Mc.
106 citations
TL;DR: An examination of the data shows the advantage of using low energy gamma rays for imaging whenever possible, and a choice must be made between a thin scintillator with its relatively good position resolution and low detection efficiency, or a thick crystal with higher detection efficiency and less satisfactory resolution.
Abstract: Photoelectric, Compton, and photopeak efficiencies have been calculated at several gamma‐ray energies for large flat sodium iodide crystals in which the thickness ranges from ⅛−2 in. Also, the loss of position resolution by gamma‐ray scattering within the scintillator is calculated, since this is of interest in the design of gamma‐ray imaging devices like the scintillation camera. An examination of the data shows the advantage of using low energy gamma rays for imaging whenever possible. They are efficiently detected by solid sodium iodide scintillators ½ in. thick, and there is little loss of resolution due to scattering of gamma rays in the scintillator. In the higher energy range, a choice must be made between a thin scintillator with its relatively good position resolution and low detection efficiency, or a thick crystal with higher detection efficiency and less satisfactory resolution.
103 citations
TL;DR: A 150-A, 4-MeV electron accelerator has been designed and constructed for use in the ''Astron'' experiment as mentioned in this paper, with a beam quality less than 10−2 rad·cm and an energy spread of ± 0.5.
Abstract: A 150‐A, 4‐MeV electron accelerator has been designed and constructed for use in the ``Astron'' experiment. Design requirements include a beam quality less than 10−2 rad·cm and an energy spread of ±0.5%; the pulse length is 0.25 μsec and the repetition rate is variable to a maximum of 60/sec. The accelerating principle used is magnetic induction. Design features and the results of preliminary operation are discussed.
100 citations
TL;DR: In this paper, the first and second order matrix equations for the magnetic optics of the midplane of uniform-field wedge magnets have been derived and a second-order matrix algebra has been developed to handle beam transport optics for multiple element systems in a manner similar to that which has been used in the past for the first-order beam transport optic.
Abstract: The first‐ and second‐order matrix equations for the magnetic optics of the midplane of uniform‐field wedge magnets have been derived. The calculations include rotated input and output wedges and curved surfaces on the input and output faces. A second‐order matrix algebra has been developed to handle beam transport optics for multiple element systems in a manner similar to that which has been used in the past for the first‐order beam transport optics.
97 citations
TL;DR: In this paper, an electromechanical feedback system for Mossbauer spectroscopy with a velocity range of 2×10−5 to 60 cm/sec is described, where a reference signal of the desired waveform (triangle, parabola, etc.) to drive the feedback system is produced by multichannel analyzer and with the help of operational amplifiers.
Abstract: An electromechanical feedback system for Mossbauer spectroscopy with a velocity range of 2×10−5 to 60 cm/sec is described. A reference signal of the desired waveform (triangle, parabola, etc.) to drive the feedback system is produced by the multichannel analyzer and with the help of operational amplifiers. The linearity of the system for a triangular velocity waveform is better than 0.5% during 98% of the half‐period.
97 citations
TL;DR: In this article, a model for the response of a photomultiplier was presented, which was obtained from direct measurements on a 56 AVP photomULTiplier and used to predict quantities such as distribution of triggering times, pulse shapes, etc.
Abstract: Section I describes steps taken to optimize the pulse shape and dynamic range from a 56 AVP photomultiplier. Section II discusses a model for the response of a photomultiplier. The parameters used in this model are obtained from direct measurements on a 56 AVP photomultiplier. Monte Carlo methods, as well as analytic techniques, are used to predict quantities such as distribution of triggering times, pulse shapes, etc. It is found, for example, that in the resolution of small time differences the predictions using the Monte Carlo method and the analytic treatment are in good agreement. The time resolution as predicted by the model is compared to experiment.
TL;DR: In this paper, an apparatus was developed which permits x-ray powder patterns to be obtained to over 500 kilobars presure using a supported tapered piston electrical resistance apparatus.
Abstract: An apparatus has been developed which permits x‐ray powder patterns to be obtained to over 500 kilobars presure. The apparatus is derived in part from the supported tapered piston electrical resistance apparatus in use in this laboratory, but the x rays are transmitted through a thin layer of LiH with suitable platinum collimation. The pressures are established by measuring the change of lattice parameter of a suitable marker mixed with the sample. These changes are then compared with volume changes obtained in shock wave work. Usual markers used to date include silver, rhodium, and palladium. Typical data for sample pressure versus average applied pressure for these metals are given. Also included is the change in lattice parameter with pressure for CsCl to 500 kilobars. The results are compared with the extrapolation of Bridgman's data.
TL;DR: The present day version of a source of low temperature, fully ionized, quiescent plasma, known as the Q•1 device, is described in this paper, where a simplified form of the theory is presented and is extended to include absorption at the walls.
Abstract: The present day version of a source of low temperature, fully ionized, quiescent plasma, known as the Q‐1 device, is described. A simplified form of the theory is presented and is extended to include absorption at the walls. The many modifications and improvements that have been made since the device was first built are described.
TL;DR: In this article, two traveling-wave rf structures, which are prototypes of devices to separate mass components of multi-BeV particle beams, have been designed and fabricated, and deflection characteristics have been studied by measuring the deflection of a 40-MeV electron beam.
Abstract: Two traveling‐wave rf structures, which are prototypes of devices to separate mass components of multi‐BeV particle beams, have been designed and fabricated. Deflection characteristics have been studied by measuring the deflection of a 40‐MeV electron beam.
TL;DR: In this paper, a survey of the properties of certain resistors made by the Speer Carbon Company to determine whether they might be suitable for resistance thermometry below 1°K was made.
Abstract: A survey has been made of the properties of certain resistors made by the Speer Carbon Company to determine whether they might be suitable for resistance thermometry below 1°K. It is found that resistors of grade 1002 in various nominal resistance values from 100–500 Ω are the most suitable for very low temperature work. Resistors of the same nominal size matched at room temperature and at 4°K have rather similar characteristics down to 0.02–0.03°K. The resistors may also be baked at a sufficiently high temperature to allow them to be sealed into apparatus using thermocuring epoxy resins. A magnetic field perpendicular to the axis of the resistors decreases the resistance at constant temperature.
TL;DR: In this article, the damping of transverse vibrations of a wire in a viscous fluid is the basis for a viscometer of high precision and versatility, which is shown to be valid for a wide range of physical parameters.
Abstract: The damping of transverse vibrations of a wire in a viscous fluid is the basis for a viscometer of high precision and versatility. A solution to the hydrodynamic problem is indicated, and shown to be valid for a wide range of physical parameters. The device is simple in operation and design, adaptable to various decay constant measuring techniques, and requires only a small volume of sample fluid. The viscosity of liquid helium II between 1.10°K and the lambda point has been measured with this technique, and shows a mean scatter of about 2%. This technique is particularly appropriate for fluids of low viscosity.
TL;DR: In this article, a small (about 20 mV) ac voltage (24 cps) is added to a slowly varying (about 1 V/min) retarding potential and the inphase ac component of the photoemission signal is measured.
Abstract: By means of the ac retarding potential method, the energy distribution of photoemitted electrons can be measured much more rapidly and conveniently than is possible by conventional dc methods. In the ac method, a small (about 20 mV) ac voltage (24 cps) is added to a slowly varying (about 1 V/min) retarding potential and the in‐phase ac component of the photoemission signal is measured. For the conventional dc techniques, it is necessary to impose very stringent stability conditions on the light source and measuring equipment. Since, in the ac method, the derivative of the I‐V characteristic is taken electronically (to give the energy distribution) and is averaged over many cycles, the stability requirements are relaxed by a large amount and data may be obtained much more quickly and conveniently. With the complete system described, resolutions of about 0.1 eV have been attained and small signal conductances (ΔI/ΔV) smaller than 10−11 mhos have been measured.
TL;DR: In this paper, the resolution of alpha particles of different energies with a liquid scintillator system has been studied for alpha particle energies of 4-7 MeV, and the best obtained value of the energy spread, the full width at half-maximum, of the pulse height distributions was 0.058 times the energy of the exciting alpha particle.
Abstract: The resolution of alpha particles of different energies with a liquid scintillator system has been studied for alpha particle energies of 4–7 MeV. In this work the best obtained value of the energy spread, the full width at half‐maximum, of the pulse height distributions was 0.058 times the energy of the exciting alpha particle. The pulse height‐energy relation for alpha particles between 4 and 7 MeV was shown to be essentially linear but not directly proportional. The quenching effects of ethyl alcohol and di(2‐ethylhexyl) phosphoric acid were measured. The linewidth and relative pulse height response of the liquid scintillator system for alpha particle excitation were studied as a function of the height and cross sectional area of the sample.
TL;DR: In this article, a system is described which facilitates a detailed study of the response of materials to shock loading under conditions of uniaxial strain, where a flat projectile plate driven into a target plate by a gas gun is monitored by shorting of a resistance wire which is inclined at a slight angle to the free surface.
Abstract: A system is described which facilitates a detailed study of the response of materials to shock loading under conditions of uniaxial strain. The uniaxial strain loading is produced by a flat projectile plate driven into a target plate by a gas gun. The resulting motion of the free surface of the target plate is monitored by the shorting of a resistance wire which is inclined at a slight angle to the free surface. An accurate time base relates the free surface data to the time of impact. The measured free surface motion may be used to determine the dynamic stress‐strain behavior of the material.
TL;DR: In this paper, a tetrahedral anvil press was developed for x-ray diffraction powder measurements at pressures to 75 kb and temperatures to 1000°C. The tetrahedra were used for determining crystal structures (KCl, Ba, and Sn), volume compressibility (Ba), lattice-parameter changes (BN), and phase diagrams (Sn) were given.
Abstract: A tetrahedral‐anvil press has been developed that permits x‐ray diffraction powder measurements at pressures to 75 kb and temperatures to 1000°C. A counting technique, rather than photographic film, is used for x‐ray detection. Sample tetrahedra of compressed LiH, boron, and boron‐filled plastic are used in place of the pyrophyllite customarily used for this purpose. Two possible entrance pupils are used for the x‐ray beam; (1) through an anvil face, and (2) through one of the compressible gaskets. Examples of the use of this versatile apparatus for determining crystal structures (KCl, Ba, and Sn), volume compressibility (Ba), lattice‐parameter changes (BN), and phase diagrams (Sn) are given.
TL;DR: In this article, a spectrophotometer for measuring fast absorption changes occurring during photo synthesis is described. But the performance of the apparatus, especially in conjunction with the CAT computer, was illustrated with the absorption change at 515 mμ in Chlorella and spinach chloroplasts.
Abstract: Details on the construction of a spectrophotometer for measuring fast absorption changes occurring during photo‐synthesis are described. Repetitive, intense light flashes with 20‐μsec duration were used to initiate the reaction. The pulse generator is capable of producing two flashes, either simultaneously or with variable time separation. The monochromatic monitoring light was split into the sample beam and the reference balancing beam. The photo‐multiplier outputs were fed to a differential circuit so that net absorption changes could be measured. Besides a wideband oscilloscope, a computer of average transients was also used to extract small signals from a high noise background. Thus, transient optical density changes as small as 0.0001 could readily be measured. The performance of the apparatus, especially in conjunction with the CAT computer, was illustrated with the absorption change at 515 mμ in Chlorella and spinach chloroplasts.
TL;DR: The high speed spectrometer described in this article allows the measurement of an extinction or reflection spectrum within the range of 2300-6000 A (respectively, 3500-7000 A) or any desired sections of same.
Abstract: The high speed spectrometer described here allows the measurement of an extinction or reflection spectrum within the range of 2300–6000 A (respectively, 3500–7000 A) or any desired sections of same. The spectra can be shown individually or in superposition (4, 8, or 16 spectra) on the screen of an oscilloscope, the x axis expressing the wavelength and the y axis the extinction. Under suitable conditions, the constancy of the zero line is better than 0.003 o.d. and allows the readings of differences in optical density less than 0.001 o.d. Examples of applications show that the apparatus is particularly suitable for following reactions in which several components simultaneously vary their absorption.
TL;DR: In this article, an ion gauge with high ionization efficiency and low input power is described, where electrons are injected by a small tungsten filament into the electrostatic field between two concentric cylinders, with energies and angular momenta such that a relatively long mean free path is achieved.
Abstract: An ion gauge with high ionization efficiency and low input power is described. In this gauge, called the orbitron, electrons are injected by a small tungsten filament into the electrostatic field between two concentric cylinders, with energies and angular momenta such that a relatively long mean free path is achieved. Only 4 μA electron current is needed to produce the same ion current obtained from 8 mA emission in a conventional Bayard‐Alpert gauge. X‐ray and photocurrents are held to low values by locating the ion collector remotely from the main source of light and x rays. The ion current is linear with pressure below 1×10−5 Torr and has been tested down to 5×10−11 Torr. The lower pressure limit has not yet been determined.
TL;DR: In this paper, a hybrid target consisting of a homogeneous mixture of reference nuclei having well-known excited states and projectile nuclei is used to determine the crossover angle at which recoil projectile particles and inelastically scattered particles from reference nucleis produce equal pulse heights.
Abstract: A method for determination of accelerator beam energies using hybrid targets is described. A target consisting of a homogeneous mixture of reference nuclei having well‐known excited states and projectile nuclei is used. Determination of the ``crossover'' angle at which recoil projectile particles and inelastically scattered particles from reference nuclei produce equal pulse heights is shown to provide a beam energy measurement. No special apparatus is required. The method is applicable over a wide range of energies. An alternative related measurement using other hybrid targets is discussed briefly.
TL;DR: In this paper, a pulsed ion source capable of delivering 10-mA proton bursts with durations of approximately 1 nsec is described, and critical design constraints are discussed and used to illustrate the general procedure for meeting various experimental requirements.
Abstract: A pulsed ion source capable of delivering 10‐mA proton bursts with durations of approximately 1 nsec is described. Critical design constraints are discussed and used to illustrate the general procedure for meeting various experimental requirements. The system consists of a Duo‐Plasmatron ion source, a lens‐chopper combination, and a klystron buncher which uses the entire accelerator as a drift path to produce bunched ion bursts at the target. The equipment has been fitted into the terminal of the ORNL 3‐MV Van de Graaff accelerator. Since no accessory bunching magnets are used, ion bursts can be delivered to many different target stations. An external diverter system is used to vary the repetition rate from 106 sec−1 down to 3×104 sec−1.
TL;DR: In this article, a study of the requirements of a mutual inductance system suitable for precise temperature measurements using about one gram of cerium magnesium nitrate was made, which was measured by a commercial version of the electronic bridge originally proposed by Pillinger, Jastram, and Daunt.
Abstract: A study is made of the requirements of a mutual inductance system suitable for precise temperature measurements using about one gram of cerium magnesium nitrate. The mutual inductance is measured by a commercial version of the electronic bridge originally proposed by Pillinger, Jastram, and Daunt [Rev. Sci. Instr. 29, 159 (1958)]. A discussion of the effects of spurious magnetic materials, of nearby paramagnetic salts, and of the vacuum jacket is given. The linearity and stability of the electronic bridge, as well as the effects of external circuitry, are also discussed. Results are given for the properties of two coil sets with cerium magnesium nitrate thermometers used to test the stability of the bridge and the validity of expressions for mutual inductance obtained in the text. It may be concluded that if solid air can be kept away from the coils, the long term instabilities for a 1‐g thermometer lead to errors of about 0.004°K−1 in 1/T. A comparison between ballistic and 17‐cps bridge measurements dow...
TL;DR: In this article, a system for the measurement of correlated energies and times of flight of fission fragments has been developed, which includes a fast response transformer coupling scheme in which the charge originating in a solidstate detector passes through the transformer primary to a low noise charge sensitive amplifier; the fast timing signal is obtained from the transformer secondary.
Abstract: A system for the measurement of correlated energies and times‐of‐flight of fission fragments has been developed. This system, adaptable for use with other charged particles as well, includes a fast‐response transformer coupling scheme in which the charge originating in a solid‐state detector passes through the transformer primary to a low noise charge‐sensitive amplifier; the fast timing signal is obtained from the transformer secondary. Noise thereby added to the linear energy signal is negligible. The measured time resolution of the system for particles in a narrow band of energies was ≲0.4 nsec, full‐width at half‐maximum. The design of the system is described, and the detailed results of performance tests, including tests with coincident 252Cf spontaneous fission fragments and energy‐time correlation measurements for bromine and iodine ions (artificial fission fragments), are given.
TL;DR: In this paper, a wideband feedback coherence control system for super-regenerative NQR spectrometers is described, which makes use of a servo motor to adjust the oscillator grid bias.
Abstract: A description is given of a wideband feedback coherence control system for superregenerative NQR spectrometers. By making use of a servo motor to adjust the oscillator grid bias, increases in rf searching band are possible. As an example, a bandwidth of 30 Mc around a center frequency of 70 Mc has been obtained. The sensitivity of the circuit to nuclear quadrupole resonance signals is high. The spectrometer will operate unattended.