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Volume 36

Issue 12 | Dec | pp. 1689-1897

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Select this Article		Sensitivity Enhancement in Magnetic Resonance. I. Analysis of the Method of Time Averaging R. R. Ernst Rev. Sci. Instrum. 36, 1689 (1965); http://dx.doi.org/10.1063/1.1719443 (7 pages) \| Cited 56 times Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract A theoretical analysis of the method of time averaging is made with special emphasis on the correlation effects caused by non‐white noise. It is shown that only in special cases is the signal‐to‐noise ratio improved exactly according to the square root of the number of successive scans through the investigated spectrum. This is shown in detail for random noise with an exponential‐cosine autocorrelation function. In the case of random noise with a pure exponential autocorrelation function, the deviation from the proportionality to the square root of the number of scans does not exceed a factor √2. If the frequency dependence of the power spectrum of the noise is given by ∣f∣^−λ, 0≤λ≤1, then the proportionality to the square root of the number of scans holds exactly. A peak in the noise power spectrum at a multiple of the repetition frequency of the scanning does affect the time averaging only if its width is smaller than the repetition frequency.

Select this Article		Sensitivity Enhancement in Magnetic Resonance. II. Investigation of Intermediate Passage Conditions R. R. Ernst and W. A. Anderson Rev. Sci. Instrum. 36, 1696 (1965); http://dx.doi.org/10.1063/1.1719444 (11 pages) \| Cited 20 times Online Publication Date: 29 December 2004 Full Text: \| Download PDF See Also: Erratum
	+ -	Show Abstract Intermediate passage conditions in magnetic resonance experiments are investigated to determine the optimum performance conditions for maximum sensitivity, particularly in connection with time averaging methods. The possible increase in signal height by increasing the sweep rate can be utilized in time averaging methods to enhance the sensitivity. The optimization of the conditions described here is based on numerical solutions of the Bloch equations. The results are given in graphical form and show the optimum conditions for many magnetic resonance experiments where the absorption mode signal is recorded. The improvement of the sensitivity, which is possible if instead of a slow passage, single scan experiment a fast passage, multiple scan experiment is made, is higher for a high ratio of the relaxation times T₁∕T₂. The possible gain is limited by the maximum allowed line broadening and line shift. The conditions are nearly optimum if the sweep rate a (cps∕sec) and the rf field strength γH₁ (rad∕sec) are related by a∕(γH₁)²=0.332. Additionally, it is shown that the shift of the resonance maximum due to the intermediate passage conditions can have a negative sign and that an increase of the sweep rate can cause a narrowing of the resonance line under certain conditions.

Select this Article		High dc Power, Solid State Switch for Pulsing an Arc Lamp Thomas A. Alexander, Earl R. Lawler, Patrick W. Wilson, and Richard I. McDonald Rev. Sci. Instrum. 36, 1707 (1965); http://dx.doi.org/10.1063/1.1719445 (3 pages) \| Cited 2 times Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract A high power, solid state device to switch direct current on and off for the controlled pulsing of a high intensity light source is described. Using 400 A (continuous rating) silicon controlled rectifiers, the switch has a design maximum power rating of 5000 A at 450 V for a 1 msec pulse.

Select this Article		Design Variables for a High Pressure Cell with Supported Taper Pistons K. F. Forsgren and H. G. Drickamer Rev. Sci. Instrum. 36, 1709 (1965); http://dx.doi.org/10.1063/1.1719446 (4 pages) \| Cited 13 times Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract A systematic investigation of the design variables for a high pressure cell with supported taper pistons has been undertaken. The variables studied include: the effect of center thickness, the effect of flat diameter and piston diameter, the pressure gradient across the flat, the pressure gradient on the taper, and the effect of different materials supporting the center. It is concluded that any scaling up in size from the dimensions used in the electrical resistance cell previously described in the literature (2.29 mm diam flat and 0.33 mm center thickness) results in a drastic reduction in pressure range. Scaling down the flat size results in a modest increase in pressure range. The pressure is remarkably independent of radius in the region of the flat which contains the electrical resistance sample. A piston with a double taper might suppy a greater degree of support for the piston tip.

Select this Article		Instrumentation for the Direct Measurement of Outer Space Short Circuit Current of Solar Cells Robert J. Lambert Rev. Sci. Instrum. 36, 1713 (1965); http://dx.doi.org/10.1063/1.1719447 (3 pages) \| Cited 1 time Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract An electro‐optical system is described for automatically measuring the spectral response of a photosensitive material or device and its output under an arbitrary light spectrum. The system has been used to obtain the spectral response and the short circuit current of solar cells in outer space sunlight. A comparison of the outer space short circuit current of n‐p silicon solar cells measured by this system and by a commercially available solar simulator shows an agreement of better than 2.1%.

SECTION LISTING

BROWSE VOLUMES

Dec 1965

Volume 36, Issue 12, pp. 1689-1897

Find articles by AUTHORNAME

Select this Article		Multiple Watt Submicrosecond High Repetition Rate Light Source and Its Application R. C. Mackey, S. A. Pollack, and R. S. Witte Rev. Sci. Instrum. 36, 1715 (1965); http://dx.doi.org/10.1063/1.1719448 (4 pages) \| Cited 11 times Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract A light source is described for generation of intense constant shape pulses of width as short as 20 nsec at demonstrated repetition rates up to 5 kc. The radiated power in the violet‐green region (3000–5000 Å) of the spectrum was measured at 0.5 W∕sr perpendicular to the lamp axis. Lamp configuration, pulser circuitry, and applications to spectroscopy and optical radar are discussed. A simple computer to facilitate the determination of fluorescent lifetimes is described.

Select this Article		Apparatus for the Simultaneous Determination of Young's Modulus and Shear Modulus at Temperatures between −190 and 600°C Philip E. Armstrong and James M. Dickinson Rev. Sci. Instrum. 36, 1719 (1965); http://dx.doi.org/10.1063/1.1719449 (3 pages) \| Cited 5 times Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract An apparatus, based on thin‐rod resonance techniques, has been used to determine both Young's and shear moduli as functions of temperature during a single experiment. The advantages of this method, its accuracy, and its limitations are discussed, along with the constructional details of the apparatus.

Select this Article		Phototaxigraph: Recording Instrument for Determination of Rate of Response of Phototactic Microorganisms to Light of Controlled Intensity and Wavelength DeArmond Lindes, Bodo Diehn, and Gordon Tollin Rev. Sci. Instrum. 36, 1721 (1965); http://dx.doi.org/10.1063/1.1719450 (5 pages) \| Cited 25 times Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract An instrument has been developed which measures the rate of phototaxis in a suspension of microorganisms by recording the increase in optical density which results when the organisms accumulate in a beam of stimulating light. Intensity and spectral quality of the actinic light, as well as of randomly scattered background illumination, can be controlled. Density changes are measured with a dual chopped beam arrangement using infrared light. Thermostatic control of the temperature of the sample is provided.

Select this Article		Sensitive Voltage Measurement and Recording System E. J. Cairns and A. D. Tevebaugh Rev. Sci. Instrum. 36, 1726 (1965); http://dx.doi.org/10.1063/1.1719451 (2 pages) Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract A direct current voltage measuring and recording system having high sensitivity (0.02 μV) and high accuracy has been developed using commercially available components. The performance of the system exceeds the nominal specifications of the individual portions of the system because of selection of components and careful shielding, guarding, and grounding practices.

Select this Article		Optical Method for Absolute Velocity Calibration of Mössbauer Spectrometers H. De Waard Rev. Sci. Instrum. 36, 1728 (1965); http://dx.doi.org/10.1063/1.1719452 (6 pages) \| Cited 18 times Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract The variable ``moiré pattern,'' formed when a 1:1 image of an 8 μ grating connected to a Mössbauer drive is reflected back onto itself, is utilized to measure the instantaneous velocity of the drive. A photodiode converts the intensity modulated light from the pattern into an electrical signal. From this signal pulses are derived that correspond to shifts of the grating by multiples of 2 μ. These pulses can be applied to a multichannel analyzer used as a part of the Mössbauer spectrometer and thus yield a velocity calibration spectrum. Instantaneous velocities can be measured with accuracies down to about 1 μ∕sec.

Select this Article		Generation and Detection of Subnanosecond Light Pulses: Application to Luminescence Studies Juan Yguerabide Rev. Sci. Instrum. 36, 1734 (1965); http://dx.doi.org/10.1063/1.1719453 (9 pages) \| Cited 17 times Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract Techniques developed to study the kinetics of very fast luminescent systems are described. These techniques include lamps which generate subnanosecond light pulses and an instrument which measures their time characteristics. The lamps are of the gaseous discharge type. The conditions of gas pressure, capacitance, and gap width necessary to achieve fast light pulses have been established for several gases and mixtures of gases with oxygen. The experimental results indicate that high pressure (10 atm or larger) and minimum stray capacitance are required for lamps filled with pure gas. A lamp filled with hydrogen, and satisfying these requirements, yields light pulses with 0.35 nsec risetime and 0.5 nsec half‐width. The time characteristics of the fast light pulses are not affected by gap width in the range 0.1–0.6 mm. Lamps containing a mixture of a gas and oxygen produce similar light pulses at total pressures much less than 10 atm. The instrument used to study subnanosecond light pulses employs a modified image converter tube. The image converter tube converts a light pulse into a photoelectron beam which is subsequently sampled by sweeping over an aperture. A complete intensity vs time curve is achieved by varying the time at which the sample is taken. The time resolution of the instrument is dependent on the sweep rate and the transit time spread of electrons in the image converter. Experimental and theoretical results indicate that the time resolution is around 0.1 nsec. The sweep is produced by a special circuit, consisting of a series of avalanche transistors, which generates sweep voltages around 600 V∕nsec and can be triggered, with time jitter less than 0.2 nsec, by an electrical pulse as short as 1 nsec and amplitude of 0.8 V. This circuit makes it possible to measure the time characteristics of any light source for which a small electrical pulse can be generated simultaneous with the light pulse. A special detecting system which measures the intensity of the sample taken from the electron beam makes it possible to measure, with high precision, very low intensity sources. Thus, the time characteristics of a light pulse which produces less than one photoelectron per pulse at the photocathode of the image converter can be measured down to one decade of its peak intensity.

Select this Article		Compressibility Measurement at High Pressures by the Inductance Coil Method A. A. Giardini, E. H. Poindexter, G. A. Samara, and J. D. Barnett Rev. Sci. Instrum. 36, 1742 (1965); http://dx.doi.org/10.1063/1.1719454 (5 pages) Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract Volume compression of isotropic solids at high pressure may be determined by measurement of the inductance of a coil wound tightly around the sample. For isotropic compression of a coil, inductance is exactly proportional to the cube root of coil volume. Cores of tungsten, strontium titanate, cadmium sulfide, and sodium chloride were compressed to 55 kbar to test coil performance. The reproducibility of compression values varied from ±5 to ±15%. The observed compressions agree closely with other published results on compression and elastic constants. For nonconductive samples, no corrections need be applied to the volumetric data.

Select this Article		Technique for Preparing Laminated Pole Figure Samples Sam Leber Rev. Sci. Instrum. 36, 1747 (1965); http://dx.doi.org/10.1063/1.1719455 (4 pages) \| Cited 3 times Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract A new method is described for making composite samples for the x‐ray diffraction, back reflection pole figure technique. Considerable savings, in material and machining costs, are realized by cutting strips, for lamination, at 45° to the rolling direction. The required reference surface is obtained, during lamination, by maintaining an angle of 54.7° between the strips and the surface developed by the cut edges. The advantages of the composite technique (better averaging, minimization of errors, and evaluation of random intensity from the pole figure data) are retained by this modification.

Select this Article		Improved Method for Measuring Small Volume Changes on Mixing Stefano Levialdi, Enzo Wanke, Umberto Bianchi, and Carla Cuniberti Rev. Sci. Instrum. 36, 1750 (1965); http://dx.doi.org/10.1063/1.1719456 (3 pages) Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract An improved method is described for measuring small volume changes on mixing a polymer with a solvent. The change in volume, occurring in a special dilatometer, causes a shift of a mercury level inside a constant cross section capillary, whose external surface is silver coated. The capillary is thus acting as a cylindrical capacitor, any change in volume being converted into a capacitance change. To eliminate the influence of thermal fluctuations, the apparatus works as a differential set. The calibration is performed by producing a known thermal expansion of a given amount of solvent (contained in the dilatometer) whose expansion coefficient is known. The sensitivity achieved is better than 1 ppm.

Select this Article		Electron Beam Evaporator for In Situ Electron Microscope Studies K. H. Olsen and T. E. Hutchinson Rev. Sci. Instrum. 36, 1753 (1965); http://dx.doi.org/10.1063/1.1719457 (3 pages) \| Cited 1 time Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract A device for evaporating metals by electron beam bombardment within the electron microscope has been developed which operates without loss of image resolution or stability. This device is particularly applicable to dynamic studies of nucleation and growth of metallic films characterized by unusually high purity and∕or high melting points. A hanging drop of molten material, formed by bombardment of the end of a vertical wire by a focused beam of 2–5 kV electrons, provides a controllable source of pure metal vapor.

Select this Article		Measurement of Capillary Blood Flow Using an Electronic Double Flash Light Source Philip N. Gallagher, Vernon E. MacRoberts, Harold E. Edgerton, Roe E. Wells, and Searle B. Rees Rev. Sci. Instrum. 36, 1760 (1965); http://dx.doi.org/10.1063/1.1719459 (4 pages) \| Cited 2 times Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract An electronic double flash unit has been constructed to measure photographically average linear velocity of blood flow in the bulbar conjunctival vessels of the human eye. Two exposures on the same photograph separated by a predetermined time delay (adjustable from 2 to 200 msec) permit computation of velocity from the displacement of red cells per delay time. The equipment is small and mobile, the procedure innocuous.

Select this Article		Rapid Determination of Electron Impact Ionization and Appearance Potentials Pasquale Martignoni, Robert L. Morgan, and Charles Cason Rev. Sci. Instrum. 36, 1783 (1965); http://dx.doi.org/10.1063/1.1719465 (5 pages) Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract All manual controls of Fox's retarding potential difference (RPD) technique have been replaced by automatic electronic controls applied to a commercial time of flight mass spectrometer. The current difference ΔI between the electron energy voltage increments, is obtained from an electronic data processor and plotted as a function of the ionizing voltage. An ionization efficiency (IE) curve is obtained in 3.8 sec or less. The sensitivity of the system permits an IE curve to be obtained in the 10⁻⁸ Torr range. An empirical formula was required to correct the present systematic error. The error was found to be −3.67+0.834x−0.0306x² for xenon, krypton, and argon, where x is the ionizing voltage of the data. This formula was used to correct the experimental water ionization potential (IP) to give 12.59±0.05 V. The spectroscopic water IP is 12.61 V.

Select this Article		Design of the Deflector for the rf Beam Separator at the Brookhaven AGS H. Hahn and H. J. Halama Rev. Sci. Instrum. 36, 1788 (1965); http://dx.doi.org/10.1063/1.1719466 (9 pages) \| Cited 4 times Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract The design of the iris‐loaded deflector for the Panofsky type rf beam separator now under construction at the Brookhaven AGS is presented. General expressions for the transverse momentum acquired by an ultrarelativistic particle traversing the deflector are derived from the field equations. Useful figures of merit (shunt impedance R, series impedance Z, quality factor Q, R∕Q, etc.) are defined. Computational results for the aperture radius a, the guide radius b, Q, R∕Q, and R as functions of group velocity v_g, the number of irises per wavelength N, and iris thickness d∕w are presented for structures with the phase velocity v_p=c. They are compared with experimental results reported from deflection tests. The design procedure of a deflector is developed for the realistic case that the shunt impedance varies with group velocity. Optimization of operating frequency f_π∕2, deflector length l, v_g, d∕w, and N is carried out. Higher order modes in iris‐loaded waveguides are investigated and methods for the suppression of mode degeneracies are outlined. The effect of the mechanical tolerances on the phase shift per cell Φ is considered. The chosen deflector structure has λ₀=10.495 cm, N=4, Φ=☒π, d∕w=0.8, 2a=48.13 mm, 2b=116.71 mm, l=3.07 m, rounded iris edges, and lateral rods as mode stabilizers. ``Cold'' measurements on cavities and waveguides are described, and a precise R∕Q perturbation method is detailed. Pertinent results are f_π∕2=2856.35 Mc, Q=8700, phase error per cell ΔΦ=2.7° rms, R∕Q=1.41 kΩ∕m, v_g∕c=−0.0204, αl≈0.5. It is concluded that a klystron pulse of ≥14 MW is sufficient to give a 1 mrad peak deflection of 18 GeV∕c particles.

Select this Article		Method for Determining the Peak Irradiance of an Optical Pump and Total Pump Energy That Is Incident Upon a Laser Crystal Thomas J. Negrelli Rev. Sci. Instrum. 36, 1755 (1965); http://dx.doi.org/10.1063/1.1719458 (5 pages) Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract A method has been developed for determining the peak irradiance of an optical pump and the total pump energy incident upon a laser crystal. Consideration is given to the variation of temperature within a copper cylindrical shell that is irradiated by an intense, short duration light pulse. A temperature distribution expression is derived which describes the variation of temperature with respect to time, at the innner wall of the shell. A copper, cylindrical shell was positioned within the helix of a xenon flash lamp and irradiated with light pulses of various intensities. The temperature rise of the inner surface was monitored with a fast response thermocouple and the temperature history displayed on an oscilloscope. The maximum temperature rise of the inner surface of the cylinder was used in conjunction with the derived temperature distribution expression and the peak irradiance and total incident energy determined.

Select this Article		Basic Properties of Electron Multiplier Ion Detection and Pulse Counting Methods in Mass Spectrometry Leonard A. Dietz Rev. Sci. Instrum. 36, 1763 (1965); http://dx.doi.org/10.1063/1.1719460 (8 pages) \| Cited 17 times Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract The critical role played by first stage gain in shaping the output pulse height distribution and detection efficiency of an electron multiplier used as an ion detector is studied theoretically and experimentally. In a well‐focused electron multiplier it is found that anode pulse height distributions observed for different ion species agree well with distributions calculated by using compound Poisson statistics. Models are developed to explain measurement bias in an electron multiplier which is used in either the dc or pulse counting modes and it is shown how these results can be applied to isotope ratio measurements. Design and operating characteristics are described for a 20 stage electron multiplier which was developed for high speed pulse counting and high detection efficiency. The surface of the first dynode is coated with a thin film of Al₂O₃ to provide a stable first stage yield of 7–9 secondary electrons∕incident ion for monatomic alkali ions with 20 kV impact energy. The polyatomic ion Na₂BO₂⁺ yields about 16 secondary electrons∕incident ion at 20 kV impact energy. Resolving time of the entire detector system is reduced to 10 nsec by using a specially designed solid state discriminator and pulse shaper. Also, a technique is described for the simultaneous detection and pulse counting of two ion beams.

Select this Article		Anemometric Characteristics of a Wire‐to‐``Plane'' Electrical Discharge Kaare J. Nygaard Rev. Sci. Instrum. 36, 1771 (1965); http://dx.doi.org/10.1063/1.1719461 (4 pages) \| Cited 1 time Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract This work describes an electric discharge in air at atmospheric pressure between a thin wire and a cathode with an elliptical cross section. The short axis of the ellipse was so small that the cathode surface facing the thin anode wire could be approximated by a plane. The cathode was split in two parts with the split parallel to the wire. When this discharge was exposed to a wind blowing perpendicular to the wire and parallel to the plane, it was found that the average displacement of the positive ions was directly proportional to the free‐stream velocity. The actual displacement could be determined by moving the wire to an upstream position such that the two parts of the cathode carried the same current. The measurements were made in a wind tunnel with velocities from about 1 to 18 m∕sec.

Select this Article		Hydrofluorination Unit for Purification of Fluoride Laser Materials Stanley I. Warshaw and Robert E. Jackson Rev. Sci. Instrum. 36, 1774 (1965); http://dx.doi.org/10.1063/1.1719462 (3 pages) \| Cited 2 times Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract An apparatus for the fluorination of hydroxyl‐ and oxygen‐contaminated fluoride compounds is described. This purification process yields oxide‐free fluorides. Optically clear lanthanum trifluoride single crystals were grown from material subjected to this treatment.

Select this Article		Bakeable, Pulsed Gas Valve for Plasma Physics Experiments D. H. Birdsall and D. E. Ping Rev. Sci. Instrum. 36, 1777 (1965); http://dx.doi.org/10.1063/1.1719463 (2 pages) \| Cited 6 times Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract A small, bakeable, magnetically actuated, pulsed gas valve has been constructed which overcomes many of the difficulties experienced with previous designs. Reproducible gas pulses of from 1 to 150 micron liters are readily attainable with the valve described.

Select this Article		Determination of Natural Tritium A. E. Bainbridge Rev. Sci. Instrum. 36, 1779 (1965); http://dx.doi.org/10.1063/1.1719464 (4 pages) \| Cited 1 time Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract The experimental methods employed at the La Jolla Natural Tritium Laboratory, University of California, for the determination of natural tritium are briefly described. The method is to assay the electrolytically enriched sample as ethane gas in a proportional counter. An error of less than 4% is obtained for samples enriched by reducing the sample volume from 2 liters to 10 ml. It is found that the previous methods of calculating the electrolytic enrichment are not necessary nor are large volume reductions necessary for most applications. In the method adapted at La Jolla the enrichment in five electrolysed samples is determined by using a sixth spiked sample. In this way it is shown that the enrichment in the sixth sample is within 4% of the enrichment in the other five and can be quickly determined.

Select this Article		Quantitative Coulometric Analyzer for Determining Dehydration Temperatures in Solids J. H. Osgood Rev. Sci. Instrum. 36, 1797 (1965); http://dx.doi.org/10.1063/1.1719467 (2 pages) Online Publication Date: 29 December 2004 Full Text: \| Download PDF
	+ -	Show Abstract Quantitative Coulometric analyses for water yield are made during thermal dehydration of rock materials and other solids. An electrolytic hygrometer cell is utilized to quantitatively measure the evolved water from a solid at known temperature as it is uniformly heated to a maximum of 1200°C. By reduction of total exposed adsorbing surface area in the retort and in the electrolytic cell coupling system, the lag between the dehydration event in the sample and cell response has been reduced to a very few seconds, thus permitting direct correlation between sample temperature and hygrometer cell current. The rapid cell response permits the resolution of discrete dehydration events and defines the temperature range through which they occur. Specific temperature‐desorption data gained with this instrument have been very helpful in gaining an understanding of the modes of constitution of water in silicates.