Showing papers in "Review of Scientific Instruments in 1966"
TL;DR: In this paper, the application of a new Fourier transform technique to magnetic resonance spectroscopy is explored, which consists of applying a sequence of short rf pulses to the sample to be investigated and Fourier-transforming the response of the system.
Abstract: The application of a new Fourier transform technique to magnetic resonance spectroscopy is explored. The method consists of applying a sequence of short rf pulses to the sample to be investigated and Fourier‐transforming the response of the system. The main advantages of this technique compared with the usual spectral sweep method are the much shorter time required to record a spectrum and the higher inherent sensitivity. It is shown theoretically and experimentally that it is possible to enhance the sensitivity of high resolution proton magnetic resonance spectroscopy in a restricted time up to a factor of ten or more. The time necessary to achieve the same sensitivity is a factor of 100 shorter than with conventional methods. The enhancement of the sensitivity is essentially given by the square root of the ratio of line width to total width of the spectrum. The method is of particular advantage for complicated high resolution spectra with much fine structure.
1,551 citations
TL;DR: In this paper, hot wire electron emissive probes are used for potential measurements in quiescent plasmas, noting plasma densities, emission levels, and plasma emission levels.
Abstract: Hot wire electron emissive probes for potential measurements in quiescent plasmas, noting plasma densities, emission levels, etc
285 citations
193 citations
TL;DR: A molecular beam electron bombardment detector is described and operational data are presented in this paper, where the detector makes use of a Paul mass filter to increase its versatility and is calibrated by the use of molecular beams of neon, argon, and krypton.
Abstract: A molecular beam electron bombardment detector is described and operational data are presented. The detector makes use of a Paul mass filter to increase its versatility. The detector is calibrated by the use of molecular beams of neon, argon, and krypton. Respective detection efficiencies are 1 atom in 2400, 320, and 80.
141 citations
TL;DR: In this paper, a system using a combination of harmonic detection and bridge techniques for the measurement of dV/dI and d2V/DI2 of superconducting tunnel junctions having resistances ranging from a few ohms to several thousand ohms is described.
Abstract: A system using a combination of harmonic detection and bridge techniques for the measurement of dV/dI and d2V/dI2 of superconducting tunnel junctions having resistances ranging from a few ohms to several thousand ohms is described. These quantities are of fundamental interest in the study of the density of electron states and phonon spectra of superconductors. This system is capable of determining σ=(dV/dI)n/(dV/dI)s, the relative dynamic conductance, where dV/dI is the dynamic resistance of the junction in the normal (n) and superconducting (s) state to within a few parts in 105. This high resolution is achieved using very small modulation levels of 60 μV rms (kT at 1°K=86 μV rms) or less. Finally, circuitry for obtaining dI/dV in the region near the energy gap using extremely low modulation levels (5 to 10 μV rms) and capable of resolving the negative resistance region is also presented. Typical data obtained with this system are shown.
137 citations
132 citations
TL;DR: Atomic scattering contribution to pulse height defect and energy dispersion of heavy ions in semiconductor detectors in this paper was found to be a contributing factor to the failure of semiconductor detector.
Abstract: Atomic scattering contribution to pulse height defect and energy dispersion of heavy ions in semiconductor detectors
108 citations
TL;DR: In this paper, the focused beam from a ''giant pulse'' laser has been used to vaporize and ionize thin samples of solid material and so provide the ion source of a time of flight mass spectrometer.
Abstract: The focused beam from a `giant pulse' laser has been used to vaporize and ionize thin samples of solid material and so provide the ion source of a time of flight mass spectrometer. Ions produced in this way have an energy spread of 0–500 V and this has necessitated employing an energy filter to obtain a resolution of about 30. Samples of 10−9 g from metal foils have been successfully analyzed and have shown comparable ionization efficiencies for a large number of metals. When this technique was applied to the analysis of crystals of organic compounds only atomic ions were observed and although the ionization efficiency of the metal atoms is again comparable, the efficiency of the other components depends critically on the power of the laser beam.
87 citations
TL;DR: In this article, a double focusing mass spectrometer was used as an ion source for a collision chamber connected to a second double focus mass analyzer, which provided both mass and energy resolution of the impacting ion beam and maximizes collection of momentum transfer products.
Abstract: An instrument for the study of ion‐neutral interactions involving momentum transfer to the product ions has been constructed. It consists of a double focusing mass spectrometer which serves as an ion source for a collision chamber connected to a second double focusing mass spectrometer. This instrument provides both mass and energy resolution of the impacting ion beam and the in‐line configuration maximizes collection of momentum transfer products, as from ion‐molecule reactions. Ion beams of experimentally useful intensity are produced over the energy range 0.2 to 100 eV with an energy spread of 0.3 eV.
86 citations
TL;DR: In this article, a different approach has been developed to measure two-body collision cross sections in the energy range from thermal to several hundred electron volts, where two molecular beams are merged and move in the same direction along a common axis.
Abstract: A different approach has been developed to measure two‐body collision cross sections in the energy range from thermal to several hundred electron volts. Two molecular beams are merged and move in the same direction along a common axis. Ion‐neutral reactions are discussed but the techniques could also be used for ion‐ion and neutral‐neutral collisions. Advantages of the merging beams technique over conventional beam‐gas and crossed beam methods include accessibility (with good energy resolution) to the energy region from a few tenths of one to a few electron volts; the possibility of measuring cross sections for two general, labile species; and relative ease in collecting and detecting products for total reaction cross section measurements. The principles of the method and details of the instrument are discussed. A cross section for the resonant charge transfer of Ar was measured. Reasonable agreement with some previous measurements, and other tests, indicate that the basic principles of a merging beams technique are valid and that the apparatus performs satisfactorily.
84 citations
TL;DR: In this paper, an elementary theory of the explosion of the foil is presented, and it is shown to agree well with experimental results, and technical problems associated with the construction of such a fast switch can be considered solved up to an energy level of at least 100 kJ.
Abstract: Rapid transfer of magnetic energy to an inductive load is usually done by discharging a condenser bank, but it can, in principle, also be done by using inductive storage. The problem then is how to open quickly a switch carrying a large current. Using a thin (10 μ) cylindrical foil of aluminum as a switch, energies of the order of 104 J have been transferred into an inductance of about 10−8 H in a few times 10−7 sec. An elementary theory of the explosion of the foil is presented, and it is shown to agree well with experimental results. Technical problems associated with the construction of such a fast switch can be considered solved up to an energy level of at least 100 kJ.
TL;DR: In this article, a cold trapped McLeod gauge, a capacitance manometer, and an ion gauge have been used simultaneously to measure gas pressure in the range 10−4 to 3×10−3 Torr.
Abstract: A cold trapped McLeod gauge, a capacitance manometer, and an ion gauge have been used simultaneously to measure gas pressure in the range 10−4 to 3×10−3 Torr. Data were obtained for He, Ne, Ar, Kr, Xe, N2, O2, CH4, CO, H2, and CO2. The capacitance manometer and pressure chamber were maintained at a constant room temperature to avoid thermal transpiration corrections. Comparison of data among gases clearly showed the systematic McLeod gauge error attributed to mercury streaming to the cold trap. The capacitance manometer and McLeod gauge readings agreed within 2% at 10−3 Torr for He, while the McLeod reading was 15% low for Xe at the same pressure. The errors for the other gases were intermediate. Spurious mercury capillary wetting effects, leading to serious errors in the McLeod gauge reading, were also noted for some of the molecular gases. The capacitance manometer was clearly superior to the McLeod gauge as a universal pressure sensor, and appears capable of reliable readings accurate to a few per cent at 10−4 Torr.
TL;DR: In this article, a capacitive detector has been developed for strain amplitude measurements of longitudinal ultrasonic waves in the frequency range from 5 to 100 MHz, and the sensitivity of the device is such that displacement amplitudes of the order of 10−10 cm can be detected.
Abstract: A capacitive detector has been developed for strain amplitude measurements of longitudinal ultrasonic waves in the frequency range from 5 to 100 MHz. The sensitivity of the device is such that displacement amplitudes of the order of 10−10 cm can be detected. As a check of the technique, quantitative measurements of the harmonic distortion of ultrasonic waves in a single crystal of germanium were made. From the results, some combinations of third order elastic constants are calculated and are compared with values obtained with the same sample by another method.
TL;DR: In this article, the suitability of copper as a low temperature calorimetric standard was investigated and the heat capacities of four samples were measured between 1.3 and 20°K with a precision of 0.1%.
Abstract: In order to establish the suitability of copper as a low temperature calorimetric standard, the heat capacities of four samples were measured between 1.3 and 20°K with a precision of 0.1%. All samples were at least 99.999% copper. One was a single crystal, one polycrystalline and annealed, one chill cast, and one polycrystalline and cold worked. The heat capacities of the annealed and chill cast samples differ by less than 0.1%. The heat capacity of the single crystal is 0.2% higher. The heat capacity of the cold worked sample is 0.7% higher at low temperatures and 0.3% higher above 10°K. It is concluded that high purity cast copper samples are excellent as low temperature calorimetric standards.
TL;DR: In this paper, a numerical mesh calculation which computes the fields and frequency for a resonant cavity has been developed, which has been used on the IBM 7094 to study 805 MHz proton linac cavities.
Abstract: A numerical mesh calculation which computes the fields and frequency for a resonant cavity has been developed. Fields for any cavity which has cylindrical symmetry, and for which the magnetic field has only a θ component, can be computed. The program has been used on the IBM 7094 to study 805 MHz proton linac cavities. These design studies have shown that cavities having curved walls and triangular drift tubes give improved performance. Calculated values of ``shunt impedance'' per unit length ZT2 for such cavities range from 32.4 MΩ/m at β=v/c=0.45 to 53.0 MΩ/m at β=1. Experimental measurements have verified the calculations.
TL;DR: In this article, the diamagnetic levitation of masses in excess of one gram has been achieved in entirely passive systems using pyrolytic graphite and permanent magnets using two vertical thrust bearing assemblies.
Abstract: Stable diamagnetic levitation of masses in excess of one gram has been accomplished in entirely passive systems using pyrolytic graphite and permanent magnets. Analytical and experimental data are given on two vertical thrust bearing assemblies. Extremely low frictional losses were determined from the rate of rotor deceleration in vacuum. Dissipation in a 4 cm diam rotor at 100 rpm was in the nanowatt range. Parametric studies are presented and possible applications discussed.
TL;DR: In this article, a single photon counting technique is used for measuring continuous light fluxes of very low intensity suitably modulated Demodulation and integration processes usually made in conventional synchronous detectors on analog signals are here performed with drift free digital operations.
Abstract: Single photon counting technique is used for measuring continuous light fluxes of very low intensity suitably modulated Demodulation and integration processes usually made in conventional synchronous detectors on analog signals are here performed with drift free digital operations The main advantage of this procedure is the possibility of improving the signal‐to‐noise ratio by very long integration times which are not limited by drifts of the electronics following the detector An analysis of the noise filtering properties of the device is given Raman light angular distributions obtained by this technique are reported as an example and noise characteristics of the device are measured and compared with the results of the theoretical analysis
TL;DR: In this paper, a bomb calorimeter for measuring the heat of detonation of 25 g charges of high explosive is described, and a complete calorimetric measurement can be made in 1 h with a precision of 0.3%.
Abstract: A bomb calorimeter for measuring the heat of detonation of 25 g charges of high explosive is described. A complete calorimetric measurement can be made in 1 h with a precision of 0.3%. Calorimetric measurements and analysis for PETN are described. The data are interpreted with the aid of thermodynamic and hydrodynamic computer calculations. For unconfined or lightly confined charges, the released energy is largely retained in the products which are shocked considerably off the Chapman‐Jouguet isentrope by reflections from the bomb wall. For heavily confined charges, the energy is largely converted to kinetic and internal energy of the confining case, and the essentially unshocked products expand along the Chapman‐Jouguet isentrope. The products of detonation are found to freeze out at 1500 to 1800°K. The heat of detonation of PETN at 298°K is 1490±6 cal/g, H2O(l).
TL;DR: In this paper, a non-Stark modulated double resonance microwave spectrometer has been constructed and tested in which frequency modulation is applied to one (strong) microwave source, the power from which passes through the sample gas but is prevented from reaching the crystal by filters.
Abstract: A practical non‐Stark modulated double resonance microwave spectrometer has been constructed and tested in which frequency modulation is applied to one (strong) microwave source, the power from which passes through the sample gas but is prevented from reaching the crystal by filters. The second source does reach the crystal but is unmodulated. The modulation is therefore transmitted to the crystal and tuned amplifier exclusively via the phenomenon of double quantum absorption. The only transitions observed were those which occur as active pairs involving a common energy level, the two frequencies being near the two source frequencies. This provides extremely specific spectra for identification in complex situations, and is a convenient way of searching for linked transitions which are useful for assignment purposes. Because no Stark electrode is needed, it is easier to construct special absorption cells such as coiled guides, high temperature cells, free space paths, etc.
TL;DR: In this paper, the transverse electromagnetic coupling of bunches of particles with each other is investigated theoretically, and the possibility of coherent instability even when the longitudinal distance between bunches is much larger than the transversal dimensions of the vacuum tank is considered.
Abstract: The transverse electromagnetic coupling of bunches of particles with each other is investigated theoretically, and shown to incorporate the possibility (due to the effect of imperfectly conducting vacuum chamber walls) of coherent instability even when the longitudinal distance between bunches is much larger than the transverse dimensions of the vacuum tank. The modes of oscillation in which the bunches move rigidly are investigated; criteria for stability, and expressions for the small amplitude growth rates under unstable conditions are presented. The case of a single bunch is considered in detail and demonstrated to be stable (even in the absence of Landau damping) provided v lies between an integer and the next higher half‐integer, where v is the number of transverse free betatron oscillations occurring in one revolution; for many bunches which are sensibly different in intensity (a criterion for this is presented), all modes are stable provided v satisfies the same restriction. For equally spaced bun...
TL;DR: In this article, an experimental high powered, Q switched, ruby laser radar or lidar designed for meteorological applications and upper atmosphere studies being conducted by the Environmental Sciences Division, Range Development Department, Pacific Missile Range, Point Mugu, California.
Abstract: This paper describes an experimental high powered, Q switched, ruby laser radar or lidar designed for meteorological applications and upper atmosphere studies being conducted by the Environmental Sciences Division, Range Development Department, Pacific Missile Range, Point Mugu, California. The lidar system equations, detailed design, operation, and recommendations for design improvements are discussed, and typical observational data are presented to illustrate the uses of this new meteorological instrument.
TL;DR: In this article, a specimen holder and a polishing unit with automatic shutoff were designed for thinning disks taken from preselected areas of large metallic specimens or from specimens with small cross sectional areas.
Abstract: A specimen holder and a polishing unit with an automatic shutoff were designed for thinning disks taken from preselected areas of large metallic specimens or from specimens with small cross sectional areas. Since the disk precisely fits the specimen holder of the microscope, a supporting grid is unnecessary and deformation from cutting and handling after thinning is eliminated. The automatic shutoff device greatly improves conditions for transmission by stopping the polishing current at the optimum time.
TL;DR: In this article, a cylindrical, electrostatic field is used to bend the ion beam of a grid and bend it around a corner to a remote collector, where the collector is shielded from the x-ray source at the grid, and the photoelectric current is reduced by a factor of 100 without incurring a loss in gauge sensitivity.
Abstract: Low pressure measurements by Bayard‐Alpert gauges are limited by x‐ray photoelectric currents at the ion collector, equivalent to a pressure reading of about 1×10−11 Torr. Through efforts to reduce this x‐ray current, the Bayard‐Alpert structure has been modified, whereby a beam of ions is extracted from the grid and bent around a corner to a remote collector. By this geometry the collector is shielded from the x‐ray source at the grid, and the photoelectric current is reduced by a factor of 100, without incurring a loss in gauge sensitivity. Bending of the ion beam is accomplished by a cylindrical, electrostatic field, in which the ion trajectories are independent of e/m. 100% modulation of the ion beam intensity is achieved by turning off the bending field, thereby permitting pressure measurements as low as 1×10−14 Torr. A total pressure of 5×10−13 Torr, nitrogen equivalent, has been measured in a stainless steel vacuum system employing ion sputtering and titanium sublimation as the means of evacuation.
TL;DR: In this article, a stopped flow temperature jump apparatus is described which permits rapid mixing of reactants and application of a temperature perturbation to the reacting system from 16 msec to several seconds or longer after mixing.
Abstract: A stopped flow temperature jump apparatus is described which permits rapid mixing of reactants and application of a temperature perturbation to the reacting system from 16 msec to several seconds or longer after mixing. The apparatus consists of a flow system with a rectangular observation chamber 1 cm in length. Electrodes are fixed above and below the observation chamber. A stopping syringe activates the time delay, switching, and triggering circuits. The triggering circuit discharges a high voltage capacitor through the solution in the observation chamber, producing a 5°K temperature jump in about 50 μsec. The response of the reacting system is monitored with absorption spectrophotometry.
TL;DR: In this paper, a discussion of what is known experimentally about the thermal contact problem at very low temperatures is given, and methods of using liquid 4He, thermometry using cerium magnesium nitrate, and solutions to the filling and isolation problems using an open capillary are discussed.
Abstract: A discussion of what is known experimentally about the thermal contact problem at very low temperatures is given. Liquid 4He is a particularly promising contact agent. Methods of using liquid 4He, thermometry using cerium magnesium nitrate, and solutions to the filling and isolation problems using an open capillary are discussed. The techniques are applied to an apparatus suitable for heat capacity measurements to below 0.02°K and to an apparatus for measurement of superconductive properties at temperatures substantially below 0.01°K. The performance of the apparatus for heat capacity and superconductivity measurements is discussed.
TL;DR: In this paper, a motion device involving magnets and phosphor bronze springs, with an adjustable mount, is described, and the circuits necessary to control the motion, and to distribute the signals from two devices operating in parallel, are outlined.
Abstract: An apparatus has been developed which permits high pressure Mossbauer resonance studies to 300 kbar. It can be operated with either the source or the absorber under pressure. The pressures are established by x‐ray diffraction measurements, and calibration curves are presented for both the supported taper and Bridgman anvils cells. A motion device involving magnets and phosphor bronze springs, with an adjustable mount, is described. Circuits necessary to control the motion, and to distribute the signals from two devices operating in parallel, are outlined.
TL;DR: In this article, the authors describe a system for measuring specific heats by a continuous warming method with accuracy at least as high as has been attained with the usual heat burst method, using this system data can be obtained very rapidly, even by unskilled operators, and reduced to final form with straightforward analysis and small amounts of computer time.
Abstract: We describe a system for measuring specific heats by a continuous warming method with accuracy at least as high as has been attained with the usual heat burst method. Using this system data can be obtained very rapidly, even by unskilled operators, and reduced to final form with straightforward analysis and small amounts of computer time. We analyze the method in terms of simple models which take into account uncertainties in the stray heat, thermal gradients in the specimen assembly, the effects of electrical noise and finite bandwidth in the thermometer circuits, and their relation to the measurement of small heat capacities. Data on lead, mercury, and gallium are presented which indicate that the models lead to fair estimates of the anticipated scatter once certain characteristics of the apparatus are known. The observed scatter varied from 0.3% for gallium, where electrical noise in the amplifiers was a dominant factor, to less than 0.1% for lead and mercury, where no single factor was conspicuous. In addition, completely independent measurements were reproducible to about 0.1%. In these experiments the measuring intervals were never greater than 1% of the absolute temperature.
TL;DR: In this article, a sweeping image spectrographic method was used to measure the magnetic field with peak values in the range from 1 to 5 MG using atomic spectral lines from an exploding wire light source situated in the experimental region.
Abstract: Rapidly varying magnetic fields with peak values in the range from 1 to 5 MG are measured by use of a sweeping image spectrographic method. Atomic spectral lines from an exploding wire light source situated in the experimental region are recorded as the magnetic field varies in a few microseconds from a moderate initial value of a few tens of kilogauss to the peak values. Field measurements are generally accurate to within 2–3% as determined by the consistency of measurements made from several different spectral lines. The sodium D lines and the indium I 4102 A line have proven to be exceptionally useful for field determinations. The highest field determined to date by this method is 5.1 MG, corresponding to a measured separation of 164 A between the centers of the shorter and longer wavelength doublets which the NaD lines assume in very high fields. The doublets, of approximately 4 A separation, are not themselves resolved.