Showing papers in "Review of Scientific Instruments in 1968"
TL;DR: The atom probe FIM as discussed by the authors is a combination probehole FIM and mass spectrometer having single particle sensitivity, which is used to identify the chemical nature of the individually imaged atoms.
Abstract: A serious limitation of the field ion microscope has been its inability to identify the chemical nature of the individually imaged atoms. The newly conceived atom‐probe FIM is a combination probe‐hole FIM and mass spectrometer having single particle sensitivity. During observation, the observer selects an atomic site of interest by placing it over a probe hole in the image screen. Pulsed field evaporation sends the chosen particle through the hole and into the spectrometer section. Preliminary results show that field evaporation of tungsten under poor vacuum conditions occurs as triply or quadruply charged WO, WN, WO2, and WN2 ions, while under better conditions doubly and possibly triply charged tungsten can be observed. Mo–Re alloys always produced doubly charged molybdenum and rhenium ions when examined in the atom‐probe. Wide applications for the study of short range order in alloys, the chemical nature of precipitates and impurity atoms, and information regarding the imaging properties of various atom species, of both the substrate and adsorbed material, are foreseen.
562 citations
TL;DR: In this article, a field emission electron source operating at a pressure of 10−9 Torr was used to produce a focused spot having a radius smaller than 50 A and providing 1000 times more intensity than a hot filament system having a similar final spot size.
Abstract: A new electron gun has been built which features mechanical and optical simplicity. Theoretically, it can produce a focused spot having a radius smaller than 50 A and provide 1000 times more intensity than a hot filament system having a similar final spot size. The increase in intensity is made possible by using a field emission electron source operating at a pressure of 10−9 Torr, which is provided (without baking) using commercially available pumps. The small spot is produced by using two properly shaped electrodes which accelerate and focus the electrons from the tip. It would take a hot filament gun and at least two additional lenses to replace this field emission gun when a spot radius less than 100 A is required. Even then the brightness of the conventional source would be too low to make use of the small spot size obtained. The optical properties for the new gun were predicted on a computer and experimentally confirmed in a new scanning electron microscope. The aperture aberration coefficient was measured to be no more than a factor of two greater than the theoretical value of 1.5 cm. A spot radius of 250 A has been measured, and this value is to be compared with the theoretical value of 150 A. Although it was convenient to measure the spot directly only at a relatively large image distance (11.3 cm), calculations imply that the gun can provide a spot radius less than 25 A when very small image distances are used. The gun can be used in pulsed operation because all optical properties are constant for a given voltage ratio so that application of the electrode voltages by means of a voltage divider provides automatic focusing for arbitrary changes in the applied voltage. The methods used to make and operate reliable high field emission tips are reviewed, and a technique is described for changing the required tip voltage to obtain a given emission current.
348 citations
TL;DR: In this paper, a gravimeter is constructed which uses the near perfect stability of superconducting persistent currents to make it a device with exceptional stability, and it is used to measure changes in the vertical position of the sphere or as changes in a feedback force, independent of the primary supporting force, which holds the sphere in a fixed position.
Abstract: A gravimeter is constructed which uses the near perfect stability of superconducting persistent currents to make it a device with exceptional stability. A superconducting sphere is levitated in the magnetic field generated by two superconducting coils. Changes in gravitational or inertial forces in the vertical direction are measured as changes in the vertical position of the sphere or as changes in a feedback force, independent of the primary supporting force, which holds the sphere in a fixed position. In its present state of development the instrument produces data which, when compared to calculated earth tides, set an upper limit on the drift rate of ±6 parts in 109 of g/day. Several possible sources of drift are discussed.
266 citations
TL;DR: In this article, a null technique was used to measure the voltage across the sample and to obtain the required precision at low frequencies, at which the normally difficult measurement of the dielectric properties of conducting materials is severely compromised by electrode polarization.
Abstract: At low frequencies, the normally difficult measurement of the dielectric properties of conducting materials is severely compromised by electrode polarization. This problem at the electrode‐sample interface arises from the modulation of the normal dc boundary potential by the passage of alternating current. A solution, permitting a conductance resolution of 1:105 for frequencies between 10 cps and 1 kc, is to use a second noncurrent‐carrying pair of electrodes to measure the voltage across the sample and to employ a null technique for obtaining the required precision. Several four‐electrode null techniques are proposed, each having certain relative merits. In all cases the resolution in capacitance is shown to be governed by a combination of the resolution in conductance, the sample properties, and the frequency of the measurement.
185 citations
TL;DR: In this article, a digital time intervalometer was developed for measuring time intervals of 1 msec or less with a time resolution of ∼200 psec, where the start signal can be delayed from 50 nsec to the full range of ∼1 msec.
Abstract: A digital time intervalometer was developed for measuring time intervals of 1 msec or less with a time resolution of ∼200 psec. The start signal can be delayed from 50 nsec to the full range of ∼1 msec. The range of the instrument is independent of the selected delay and can be set to cover intervals from 100 nsec to ∼1 msec. The instrument is unique in that analog time expansion is used to measure very accurately the time phase between a 20 MHz oscillator and the start and stop signals.
162 citations
TL;DR: A new method was developed for determining the position of ionizing events by measuring the risetime of output pulses from detectors having high resistance collectors, and it gives good linearity and spatial reso...
Abstract: A new method was developed for determining the position of ionizing events by measuring the risetime of output pulses from detectors having high resistance collectors. Several prototype detectors, such as proportional counters, pulse ion chambers, and surface barrier detectors, were constructed and tested for this purpose. These detectors were treated as infinite RC lines with distributed parameters, and the position‐dependent risetime of the output pulses was measured by crossover timing after double RC differentiation. With these detectors the impact locations of x rays, thermal neutrons, and alpha particles were determined. The spatial uncertainty obtained with 400 mm long proportional counters was 0.5 mm FWHM, for 22 keV x rays, 6 mm FWHM for thermal neutrons, and 0.66 mm FWHM for 242Cm alpha particles. A spatial uncertainty of 1.25 mm FWHM was obtained with a pulse ion chamber for 242Cm alpha particles. This method of determining the position of an ionizing event gives good linearity and spatial reso...
150 citations
TL;DR: In this paper, the design and operation of resonant linear accelerator tanks suitable for use in high energy proton and electron linacs is described and the synthesis of the side coupled cavity chain, a biperiodic chain which combines high acceleration efficiency with π/2 mode field stability, is described.
Abstract: The design and operation of resonant linear accelerator tanks suitable for use in high energy proton and electron linacs is described. It is shown that construction of these tanks to operate in the π/2 mode yields systems with extraordinary field stability. Theoretical expressions and corresponding experimental observations are obtained for the behavior of cavity chains operating in the π/2 mode. The synthesis of the side coupled cavity chain, a biperiodic chain which combines high acceleration efficiency with π/2 mode field stability, is described. Extensions of π/2 mode operation to nonperiodic chains is also demonstrated.
132 citations
120 citations
TL;DR: In this paper, a multi-cavity model was proposed to analyze the radial beam break-up observed in terms of long, multi-section electron linear accelerators using a multiscale model.
Abstract: The phenomenon of radial beam break‐up observed in terms of long, multi‐section electron linear accelerators has been analyzed using a multi‐cavity model. In this model the source of regeneration due to backward wave amplification is ignored. The dominant phenomenon involves build‐up of radial modes in each cavity as coupled by the electron beam. The resulting differential equations are integrated by the method of steepest descent and by a numerical iteration method. Scaling laws in terms of the pulse length, beam intensity, energy gradient, and length of the structure are derived.
115 citations
TL;DR: In this paper, the calculated performance of electrostatic analyzers of the cylindrical and spherical deflection type are compared. And it is shown that considering geometrical terms through the third order the cylinrical device is significantly superior.
Abstract: The calculated performance of electrostatic analyzers of the cylindrical and spherical deflection type are compared. It is shown that considering geometrical terms through the third order the cylindrical device is significantly superior.
114 citations
TL;DR: In this article, power supplies used in field-cycling nuclear resonance experiments are described, which are used to switch an air coil from high field to low field as rapidly as possible, then back to high field after a short time.
Abstract: Power supplies used in field‐cycling nuclear resonance experiments are described. These are used to switch an air coil from high field to low field as rapidly as possible, then back to high field after a short time. This sequence must be repeated every few seconds or minutes. An example of a simple regulator is described, and methods of output switching with relays are discussed. A circuit is described which delivers up to 10 kG (15 A) in a 2.6 cm i.d. superconducting coil with a switching speed of 5×105 G/sec and an accuracy probably as great as 1 G. Speed is achieved by automatic connection, during up or down switching, of energy storage capacitors across the magnet, operating at much higher voltage than the steady‐state voltage level across the magnet and pass transistors.
TL;DR: In this article, an apparatus for measuring magnetic susceptibility by the Faraday method is described, which is capable of measuring susceptibilities ranging from 0.01×10−6 to 500 × 10−6 emu/g over a temperature range of 5 to 300 K, in fields up to 10 kOe, with a precision of 0.2%.
Abstract: An apparatus for measuring magnetic susceptibility by the Faraday method is described. It is capable of measuring susceptibilities ranging from 0.01×10−6 to 500×10−6 emu/g over a temperature range of 5 to 300 K, in fields up to 10 kOe, with a precision of 0.2% and an accuracy of 1%. Various problems associated with the measurements, such as thermomolecular flow, ferromagnetic impurities, and electrostatic forces, are discussed It is shown that problems arising from thermomolecular flow can be avoided by controlling the pressure of exchange gas. Correction for ferromagnetic impurities involves extrapolating the susceptibility vs 1/H to infinite field. Several methods for minimizing the problems caused by electrostatic force are discussed. The versatility of the balance is demonstrated by measurements made on NiTiO3 (χmax=229×10−6 emu/g) and K0.3 MoO3 (χ≈0.06×10−6 emu/g).
TL;DR: The turbulent wake of a spherical surface was utilized as part of a mixer for fast reaction studies and highly efficient mixing was achieved for 120 cP solutions as well as aqueous solutions.
Abstract: The turbulent wake of a spherical surface was utilized as part of a mixer for fast reaction studies. The mixer is capable of mixing two solutions within 100 μsec at a flow velocity of 30 m/sec. Optical and thermal methods were used to study the mixer. Highly efficient mixing was achieved for 120 cP solutions as well as aqueous solutions.
TL;DR: In this article, it was shown that the magnetic field homogeneity can be described satisfactorily by properties of the observed spectral line shape only, and that the moments, peak height, and signal energy of a typical resonance line can be adjusted independently for any field configuration.
Abstract: Methods for the measurement and control of magnetic field homogeneity are described. They are designed for application in magnetic resonance spectroscopy. It is shown that field homogeneity can be described satisfactorily by properties of the observed spectral line shape only. Possible criteria include the moments, peak height, and signal energy of a typical resonance line. The moments are equivalent to the Lp norm of the magnetic field configuration. Only the second moment and related criteria allow the construction of a complete set of noninteracting shims which can be adjusted independently for any field configuration. The other moments may provide noninteracting control for certain simple field configurations only. For a resonance line with a sufficient natural width, peak height and energy can be related to the second moment and may also give noninteracting control. Iterative methods for automatic control by means of digital computers are described and applied to a high resolution nuclear magnetic resonance spectrometer.
TL;DR: In this paper, collision-free quiescent plasmas are produced in a magnetic mirror geometry by applying ∼50 WUhf power to a novel coupling structure which surrounds one section of the plasma.
Abstract: Collision‐free quiescent plasmas are produced in a magnetic mirror geometry by applying ∼50 W uhf power to a novel coupling structure which surrounds one section of the plasma. The plasma characteristics are favorable for studies of waves, diffusion, stability, and turbulence.
TL;DR: In this article, the conditions required for resolving a given beam speed distribution were evaluated by calculating the time-of-flight (TOF) signal for a finite open time of the beam shutter, and design criteria for a beam chopper and detection system were discussed in terms of the resolution, the range of speeds to be measured, and the optimum signal to noise ratio.
Abstract: Conditions required for resolving a given beam speed distribution were evaluated by calculating the time-of-flight (TOF) signal for a finite open time of the beam shutter. Design criteria for a beam chopper and detection system are discussed in terms of the resolution, the range of speeds to be measured, and the optimum signal to noise ratio. A TOF system for detection of high intensity molecular beams with large speed ratios, as well as for low intensity scattered beams, is described. Experimental results are presented.
TL;DR: In this paper, a method for the measurement of turbulence level and turbulent shearing stress by a single, continuously rotated, hot wire anemometer is presented, where emphasis is placed on the simplicity in the measuring procedure and on the accuracy in the results obtained.
Abstract: A convenient method for the measurement of turbulence level and turbulent shearing stress (u2¯,v2¯,uv¯) by a single, continuously rotated, hot wire anemometer is presented. Emphasis is placed on the simplicity in the measuring procedure and on the accuracy in the results obtained. When comparing the results of Reynolds stress measurement in fully developed turbulent pipe flow, good agreement was found with values calculated from the measured pressure drop (skin friction coefficient) along the pipe.
TL;DR: The vibrating sample magnetometer (VLFVSM) as discussed by the authors is a magnetometer specifically adapted for magnetic moment measurements in high dc fields, where the sample is moved at very low frequencies between series opposing detection coils, the induced voltage is integrated, and each cycle is recorded so that the output can be further time-averaged.
Abstract: A vibrating sample magnetometer is described which is specifically adapted for magnetic moment measurements in high dc fields. The sample is moved at very low frequencies between series opposing detection coils, the induced voltage is integrated, and each cycle is recorded so that the output can be further time‐averaged. Two novel aspects make this instrument particularly useful for high field measurements. First, the sample is moved beyond the center of the detection coils so that positioning errors, forces, and other incidental effects are eliminated. Second, a precise reference balance voltage is synchronously applied to the output signal to permit high‐resolution differential measurements of magnetic moment. In addition to a detailed description of the basic VLFVSM, a general discussion of flux integration techniques is presented. Operation of the VLFVSM with field modulation superimposed, variable temperature, variable pressure, additional electronic filtering, and under swept‐field conditions is discussed. Mechanical and electronic details and typical operating characteristics are included. The entire magnetometer has moderately high sensitivity, is extremely rugged, versatile, and eliminates sources of error present in many sample extraction techniques. All components, excluding the mechanical systems associated with the sample, are available commercially. This magnetometer has been applied to practically all types of high field magnetic moment measurements including differential susceptibility measurements in metals, alloys and insulators, superconductors, and highly anisotropic materials such as the rare earth metals.
TL;DR: A zero crossing technique has been employed to reduce energy‐dependent time errors when detecting gamma rays with Ge(Li) detectors to minimize timing errors associated with pulse shape variation.
Abstract: A zero crossing technique has been employed to reduce energy‐dependent time errors when detecting gamma rays with Ge(Li) detectors. The timing errors associated with pulse shape variation have been evaluated so that circuit parameters might be chosen to minimize those errors. Results of coincidence measurements using a plastic scintillator and a Ge(Li) detector are presented. Typical results using an 8 cc planar detector are 0.8 nsec FWHM at 2.75 MeV, 2.8 nsec FWHM at 511 keV, and 1.5 nsec variation in coincidence peak position from 500 keV to 2.75 MeV.
TL;DR: In this article, the influence of energy analyzer transmission function on measured field emission energy distributions has been evaluated by folding a Gaussian transmission function into the field emission total energy distribution, and the resulting distributions at 0, 4.2, 20.3, 77, and 300 K are plotted as a function of the field and work function dependent parameter d, and for the special case φ=4.40 eV, F=3.0×107 V/cm.
Abstract: The influence of energy analyzer transmission function on measured field emission energy distributions has been evaluated by folding a Gaussian transmission function into the field emission total energy distribution. The resulting distributions at 0, 4.2, 20.3, 77, and 300 K are plotted as a function of the field‐ and work‐function‐dependent parameter d, and for the special case φ=4.40 eV, F=3.0×107 V/cm. A criterion is established for determining the width of an analyzer transmission function from distributions measured at the above temperatures. It is shown that the slope of the log of the energy distribution is changed by less than 1% when the analyzer width is changed from 0 to 100 mV.
TL;DR: In this article, a Bendix time-of-flight (TOF) mass spectrometer was used to investigate ion-molecule reactions at ion source pressures up to about 1 Torr.
Abstract: Extensive modifications of a Bendix time‐of‐flight mass spectrometer have been accomplished to permit investigation of ion‐molecule reactions at ion source pressures up to about 1 Torr. In contrast with previous attempts to operate a TOF mass spectrometer, the present method employs a continuous electron beam and a dc extraction field in an ion source similar to those used in magnetic mass spectrometers. The master pulse initiating the timing cycle for mass analysis is applied to a focus grid in the low pressure region external to the source chamber and an auxiliary positive blocking pulse is applied to limit the sampling region during the ``on'' cycle. This modification eliminates degradation of instrument performance resulting from charge exchange and other secondary processes during ion acceleration, thereby extending the pressure range over which the ion source is operable by about two orders of magnitude and simultaneously increasing significantly resolution at moderate pressures. Additionally, a nov...
TL;DR: A stopped flow apparatus for the study of fast reactions in solution is described and the measured dead time was 270 μsec with an uncertainty in the measurement of 50 μsec.
Abstract: A stopped flow apparatus for the study of fast reactions in solution is described. The measured dead time was 270 μsec with an uncertainty in the measurement of 50 μsec. At 410 mμ and an optical density of about 0.09 a change of 0.0044 optical density units could be observed at a flow velocity of 30 m/sec through a 3.0 mm observation tube. Ten milliliters of each of the two reagents are required to fill the system, and less than 1.0 ml of each needs to be expended per experiment.
TL;DR: In this paper, a new isothermal titration calorimeter was designed to facilitate the study of heat effects of reaction and solution at constant temperature, which can be used to study endothermic or exothermic processes at temperatures at a given point in the Calorimeter constant to ± 0.0002 C°.
Abstract: A new isothermal titration calorimeter has been designed to facilitate the study of heats of reaction and heats of solution at constant temperature. With this calorimeter, endothermic or exothermic processes can be studied at temperatures at a given point in the calorimeter constant to ±0.0002 C°. Heat effects are compensated by balancing the heat effect of the process taking place in the calorimeter against a variable heater and a constant cooling Peltier device. The calorimeter was tested by measuring the heat of ionization of water and the heat of dilution of aqueous HClO4 solutions. For these systems heats were measured to an accuracy of ±0.02 cal.
TL;DR: In this paper, the authors used a 1P28 photomultiplier (PM) tube plus a solution of rhodamine B in ethylene glycol (RhB solution) to measure photon flux from pulsed and steady state light sources over a wide range of wavelength and flux.
Abstract: This paper presents a technique for fast and accurate measurement of photon flux from pulsed and steady state light sources over a wide range of wavelength and flux. The technique uses a 1P28 photomultiplier (PM) tube plus a solution of rhodamine B in ethylene glycol (RhB solution). The flux to be measured is absorbed by the rhodamine solution and the resultant rhodamine fluorescence is measured by the PM tube. The solution absorbs completely all photons below 6000 A and fluoresces with constant fluorescence spectrum and fluorescence quantum efficiency for incident wavelengths from 6000 to at least 2500 A. These properties of the RhB solution result in a PM tube‐RhB solution detecting system with constant photon sensitivity from 6000 to 2500 A. A large range of flux can be measured by adjusting the distance between the fluorescent solution and the PM tube so as to maintain the tube current within limits of stable operation. An RhB detector with a given distance between the RhB solution and the PM tube pho...
TL;DR: In this article, a temperature jump apparatus for relaxation studies in electrolytic solutions has been developed with laser heating and conductivity readout, which is suitable for quantitative studies of relaxation times in the range 10−1 to 3×10−6 sec.
Abstract: Temperature‐jump apparatus for relaxation studies in electrolytic solutions has been developed with laser heating and conductivity readout. The apparatus is suitable for quantitative studies of relaxation times in the range 10−1 to 3×10−6 sec. With a ruby laser, an appropriate solute must be added to aqueous solutions lacking a colored solute to adjust the optical density of the solution to an appropriate value. With a neodymium laser, the intrinsic absorption of water in aqueous solutions is adequate.
TL;DR: In this paper, an apparatus was developed for producing an atomic beam of potassium in the energy range of 0.2 to 45 eV (1000-15 000 m/sec).
Abstract: An apparatus has been developed for producing an atomic beam of potassium in the energy range of 0.2 to 45 eV (1000–15 000 m/sec). The technique used here is cathode sputtering. With a velocity selector (spread, 6.7%; maximum rotational speed, 48 000 rpm), both the signal of a Pt‐W detector and an energy independent one are measured as a function of the velocity of the beam particles.
TL;DR: In this paper, it was shown that large magnetic losses in a sample broaden the paramagnetic line in EPR without changing its g value, and the expressions for this ''extra line width'' for two experimental cases: (1) the oscillator frequency is stabilized to an external reference cavity; (2) the O(O(O) frequency is stabilised to the sample cavity.
Abstract: This paper shows that large magnetic losses in a sample broaden the paramagnetic line in EPR without changing its g value. The expressions are derived for this ``extra line width'' for two experimental cases: (1) the oscillator frequency is stabilized to an external reference cavity; (2) the oscillator frequency is stabilized to the sample cavity. The ``extra line width'' is shown to be a simple monotonic function of the static magnetic susceptibility χ0, the Larmor frequency, the filling factor and the loaded Q of the cavity. From this, χ0 can be determined. The theory is compared with experiments on Cu(HCOO)2·4H2O and good agreement is obtained. The magnetic susceptibility of Cu(HCOO)2·4H2O is measured as a function of temperature by this technique. A weak broad maximum is observed around 70°K, in agreement with the results obtained by the usual methods.
TL;DR: In this paper, a commercial quartz microbalance has been calibrated via simultaneous comparison with a reference vacuum electrobalance, and the response function δf/δm was determined to exhibit asymmetries about the central axes.
Abstract: A commercial quartz crystal microbalance has been calibrated via simultaneous comparison with a reference vacuum electrobalance. Aluminum, copper, and gold thermally deposited on 10 MHz AT‐cut oscillators gave a composite linear calibration to a precision of ±0.2%. For a uniformly distributed deposition, the ratio K of the fractional change of mass Δm/m to the fractional change of frequency Δf/f is shown to be 0.991 with a probable error of 0.6% for a configuration having peripheral contact restraints of the oscillators. The response function δf/δm (sensitivity variation over the face of the crystal) was determined to exhibit asymmetries about the central axes.