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Journal of Applied Physics

Issue 7 • Date Jul 1977

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Displaying Results 1 - 25 of 106
  • Issue Table of Contents

    Page(s): toc1
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    Freely Available from IEEE
  • X‐ray‐sensitive vidicon tube for low‐level radiation imaging

    Page(s): 2655 - 2659
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    A new type of imaging tube for x rays and γ rays in the 80‐keV and higher energy range is described. The tube has the ability to image low flux levels of incident radiation by the process of charge integration in the target plate while the reading electron beam is turned off. The target plate consists of a layer of lead deposited on a substrate. The lead layer converts a portion of the incident radiation into photoelectrons. These photoelectrons travel through a low‐density layer of cesium iodide deposited on the lead layer and create secondary electrons. An electric field maintained across the cesium iodide layer causes the secondary electrons to be collected by the conductive backing of the target plate, thereby leaving a charge pattern on the surface. A scanning electron beam neutralizes this charge pattern, resulting in the flow of signal current. The technique of obtaining maximum signal current for a given radiation energy is one of optimizing the thickness of the lead layer and the thickness and density of the cesium iodide layer. Experiments designed to determine the optimal values of these parameters are described. Imaging studies carried out using an x‐ray machine as well as a 133Xe radioactive source are described. View full abstract»

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  • Analysis and some applications of a condenser microphone used as an ionization chamber for intense α fluxes

    Page(s): 2660 - 2667
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    It is shown that intense α fluxes, when incident on a condenser microphone, produce noise, and that this noise is due to α ionization in the capacitor interelectrode space which acts as a tiny ionization chamber. Statistical analysis of random events is presented which leads to relations between this noise, incident α fluxes, and α ionization efficiency. Applications of these results to α‐activity measurement and absolute Bragg‐curve determination are discussed. α activities from 100 μCi/cm2 to several Ci/cm2 can be measured and good spatial resolution can be achieved using small microphones. View full abstract»

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  • Energy analysis of H- ions from a hollow‐discharge duoplasmatron

    Page(s): 2668 - 2672
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    Energy spectra of H- ions from a HDD source operating in mixtures of helium, hydrogen, and cesium reveal that negative ions are generated by a volume process and by a surface process. A marked difference was observed in the pressure dependence of the low‐ and high‐energy groups, corresponding to the volume and the surface processes, respectively. The active surfaces could be identified. Some evidence that, besides collisional attachment processes, ion‐molecular reactions have an influence on the yield of H- ions in volume reactions could be found. View full abstract»

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  • Efficient laser ionization of sodium vapor—A possible explanation based on superelastic collisions and reduced ionization potential

    Page(s): 2673 - 2675
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    The recently observed efficient ionization of sodium vapor by a laser tuned to the sodium resonance line can be explained in terms of the large population of resonance‐state atoms created by laser‐induced radiative equilibrium. This large population of excited atoms represents (a) a reservoir of energy that can rapidly be transferred to the free electrons via superelastic collisions and (b) a source of pseudo‐ground‐ state atoms possessing a much reduced ionization energy. Three‐photon ionization is proposed as the mechanism for creation of the primary pool of free electrons. View full abstract»

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  • Atomic fluorescence of sodium under continuous‐wave laser excitation

    Page(s): 2676 - 2680
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    The tunable continuous‐wave (cw) dye laser has been shown to be capable of producing saturation conditions for sodium in an air‐acetylene flame. The experimental evidence indicates that the sodium doublet is a reasonably good approximation of a two‐level system. Saturation of the sodium 589.6‐nm line was observed at laser spectral irradiances of 1013 erg s-1 cm-2 nm-1 and greater. Measurements of the absolute‐maximum fluorescence radiance under saturation conditions have been used to measure sodium concentration profiles in air‐hydrogen and air‐acetylene flames with spatial resolution on the order of 0.01 cm. View full abstract»

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  • Transition moments and integrated intensities of HCN(ν13) and DCN(ν13) combination bands

    Page(s): 2681 - 2683
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    The absolute infrared integrated intensities of HCN(ν13) and DCN(ν13) summation bands have been measured using the pressure broadening technique. From the measured integrated intensities, transition moments were determined. The values obtained were 1.1±0.1 cm-2 atm-1 and 0.9±0.1 cm-2 atm-1 at 298 °K, respectively, for the HCN and DCN intensities and 1.8×10-41 erg cm3 and 1.9×10-41 erg cm3 for the square of the transition moments. The values reported are 50 times smaller than the corresponding transition moment for CO2 at 10.6 μm, hence it will be considerably more difficult for the HCN/DCN laser to attain threshold. View full abstract»

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  • A short‐period helical wiggler as an improved source of synchrotron radiation

    Page(s): 2684 - 2691
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    A new kind of wiggler is proposed as an improved source of synchrotron radiation from high‐energy electron storage rings. The electrons are made to travel in a short‐period helix by a transverse helical magnetic field. The radiation spectrum produced is calculated and it is shown that the helical wiggler design could produce a total intensity (photons sec-1 per unit bandwidth) improvement of several hundred and a brightness (photons sec-1 per solid angle per unit bandwidth) improvement of 4×104 over the present state of the art in synchrotron radiation sources. View full abstract»

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  • Orbits and fields in the helical wiggler

    Page(s): 2692 - 2698
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    The ’’helical wiggler’’ is a device in which relativistic electrons pass through a transverse magnetic field whose direction revolves with distance along the beam axis. In this paper we discuss the electron orbits in this device. The field patterns and necessary current distributions are established. Finally, the question is treated as to whether this device can be incorporated into a storage ring without destroying the circulating beam. It is concluded that there is reason to expect satisfactory performance from helical wigglers in storage rings. View full abstract»

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  • An efficient organic crystal for nonlinear optics: methyl‐ (2,4‐dinitrophenyl) ‐aminopropanoate

    Page(s): 2699 - 2704
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    The first member of a new family of materials for nonlinear optics, methyl‐ (2,4‐dinitrophenyl) ‐amino‐2 propanoate (MAP), has been prepared and its linear and nonlinear optical properties have been investigated. High nonlinear coefficients result from the favorable electronic properties of the MAP molecule, as well as its chirality, which ensures a noncentrosymmetrical crystal structure. This material is phase matchable over its entire transparency range, and its figure of merit d2/n3 for parametric interactions is 15 times larger than LiNbO3. The optical damage threshold is higher than 1 GW/cm2 for 10-8‐sec pulses at 1.06 μm. The 30% second‐harmonic conversion efficiency has been observed in a 1‐mm‐thick crystal. In addition, we present an extension of the analysis of Maker fringes to monoclinic crystals of point group 2. View full abstract»

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  • High‐pressure pulsed electrical CO laser

    Page(s): 2705 - 2711
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    The design and performance of a 16‐l high‐pressure pulsed electric discharge CO laser is reported. The gas was excited using the electron‐beam sustained discharge technique. Cryogenically cooled gas flowed subsonically through a room‐temperature cavity. Thermal isolation was provided by the formation of free convection boundary layers on the warm flow walls which preserved the cryogenic gas temperature and maintained good medium uniformity. Beam‐quality measurements indicated better than 1.5 times diffraction‐limited peformance with single pulse energies of 1600 J and an electrical efficiency of approximately 40%. Comparisons are made between the actual laser performance and predictions based on the CO laser kinetics code. View full abstract»

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  • Laser power and gain measurements on the sequence bands of CO2

    Page(s): 2712 - 2717
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    An experimental technique is reported which converts a conventional cw CO2 laser into one which lases on a series of new laser bands. These bands are identified as the (0002–[1001,0201]I,II) and the (0003–[1002,0202]I,II) sequence bands of CO2, and lie in the 10‐μm wavelength region. The technique involves placing a cell containing hot CO2 in the laser cavity to suppress the regular 0001 bands. We report the first detailed power and gain measurements on the new laser bands. More than 80 laser lines have been observed in the 0002 bands, with cw output powers as high as 10 W. Gain measurements are reported for a variety of discharge conditions, and gain coefficients greater than 0.3%/cm have been obtained. We have also observed several laser lines in the 0003 sequence band of CO2. Possible applications of the new laser lines are discussed, particularly their use in determining vibrational temperatures in CO2 discharges. View full abstract»

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  • Output power and intensity distribution of a transverse‐flow CO2 laser

    Page(s): 2718 - 2722
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    We have measured the intensity distribution of a transverse‐flow CO2 laser along the flow direction and the dependence of its output power on the cavity width. The experiments were performed with a transverse‐flow CO2:N2 laser chemically excited by the reaction of nitric oxide with atomic nitrogen. The intensity distribution is found to be of a multimode structure, fairly symmetrical about the optical axis. The overall output power for a given flow velocity and gas mixture is found to increase with increasing cavity width, up to a maximum value, and then it diminishes with any further increase of the cavity width. These results do not agree with those expected from a simple geometric‐ray model. On the ohter hand, our results conform qualitatively with those expected from a coupled multimode approach. The main differences between the two approaches are discussed, and simple arguments are presented to illustrate the limitations of these two approaches. View full abstract»

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  • A free‐floating superconducting bolometer—A sensitive heat‐pulse detector

    Page(s): 2723 - 2728
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    A free‐floating (no substrate) granular aluminum superconducting bolometer has been made and tested. Sensitivity and time‐constant measurements were compared with those of similar bolometers fabricated on glass and Al2O3 substrates. The responses were first studied with the bolometer isolated in a vacuum chamber which was immersed in a superfluid liquid‐helium bath and cooled by conduction through the contact leads, and again after incremental increases of helium gas were introduced into the sample chamber. The measurements show that for low gas pressures (≲10-4 cm Hg) the floating bolometer was between one and two orders of magnitude more sensitive than identical bolometers on substrates. With increasing gas pressure, the formation of a superfluid helium film of an approximate thickness of three atomic layers caused a reduction of the floating bolometer sensitivity by nearly two orders of magnitude. The effect of bolometers on substrates was, on the other hand, only 30%. The results provide strong evidence that the Kapitza conductance into helium occurs in the first two or three atomic layers. View full abstract»

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  • Spall studies in uranium

    Page(s): 2729 - 2737
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    We have studied spall by observing the effect of spallation on the free‐surface velocity of a plate‐impact target. We believe that the spall signal is a sensitive measure of the damage done to the target. We have formulated a simple theoretical model and incorporated it in a hydrodynamic computer code, to simulate the first few stress reverberations in the target as it spalls. The simple model successfully describes the principal features of our measurements in uranium and in a few other metals. View full abstract»

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  • Extraction and propagation of rotating intense proton beams from a magnetically insulated diode

    Page(s): 2738 - 2752
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    A magnetically insulated parallel‐plate geometry was used to produce intense rotating beams of protons. It is shown that even though the diode is not in equilibrium with respect to the drifting electrons, a decrease in the perveance by more than a factor of 40 could be produced by the application of the field. Operation of the diode is accompanied by strong bursts of microwave radiation. Efficiencies over 50% were achieved in accordance with theory. Ion current‐density enhancements above the Child‐Langmuir limit that appear directly attributable to drifting electron space‐charge effects were observed. Typically, more than 3×1015 protons were extracted per pulse. Space‐charge neutralization of the extracted beam appears complete and inductive electron backcurrents were not detected. The beam propagates in accordance with geometric predictions and at least 67% of the beam completes one revolution. A field reversal factor of 1.5% (ΔB=140 G) was obtained. It is shown that this injector can easily be scaled to the parameters needed to produce a self‐contained ion ring. View full abstract»

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  • Evolution of a CO2‐laser‐produced cadmium plasma

    Page(s): 2753 - 2761
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    The evolution of a CO2‐laser‐produced cadmium plasma formed in the presence of a background gas at low pressure is described. The processes which give rise to plasma formation, spectral emission, expansion, and internal structure are discussed. The suitability of such a plasma as a potential laser medium is considered and some of the most likely and least likely regions and conditions for achieving gain are identified. View full abstract»

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  • Analytic solutions of a model for radiation‐induced conductivity in insulators

    Page(s): 2762 - 2770
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    A model for radiation‐induced bulk electrical conductivity in insulators is developed and discussed. The characteristic equations are coupled nonlinear stiff differential equations for which analytical solutions are presented. Solutions are given for the buildup of conductivity during constant irradiation and the decay of conductivity following interruption of irradiation. The long‐time asymptotic results agree favorably with previous experimental data. View full abstract»

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  • Growth and propagation mechanism of 〈110〉‐oriented dark‐line defects in GaAs‐Ga1-xAlxAs double heterostructure crystals

    Page(s): 2771 - 2775
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    Application of external stress on a double heterostructure (DH) crystal is used to induce 〈110〉‐oriented dark‐line defects (DLD). The stress is applied by using a four‐point mechanical bending apparatus. Resulting DLD formation is found to depend on stress direction and DH crystal orientation. This asymmetric DLD introduction can be explained by the difference in glide motion between α and β dislocations. It is shown that a threshold stress exists for the DLD formation. This threshold stress and the growth velocity of the DLD’s strongly depend on optical pump intensity. Extension of the DLD’s into the ternary passive layers is observed by x‐ray topography and phase‐contrast microscopy. This observation suggests that stresses caused by local heating at the site of a defect play an important role in inducing 〈110〉 DLD’s. These experimental results lead to the conclusion that dislocation glide processes are responsible for 〈110〉‐DLD propagation. View full abstract»

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  • Effect of ion bombardment on the surface composition of Cu‐Ga alloys studied by differential reflectometry and AES

    Page(s): 2776 - 2778
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    Measurements have been made on the effects of ion‐beam milling on the surface of Cu‐Ga alloys using a technique in which the optical reflectivity of an ion‐bombarded surface is compared with a nonbombarded region. The differential‐reflectometry method has a sensitivity to less than a 1% change in composition in the surface layer and probes the surface to a depth order of 50–100 Å corresponding to the optical skin depth. The results have been correlated to changes in the peak heights of Cu and Ga measured by Auger electron spectroscopy. In this way it has been found that negligible selective sputtering of the Cu and Ga occurs when the alloys are ion bombarded with 2‐keV argon ions. The ratio of the AES peak heights due to Ga and Cu from the oxide differed from that of the alloys by about a factor of 2. View full abstract»

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  • Electrical measurement of the lateral spread of the proton isolation layer in GaAs

    Page(s): 2779 - 2783
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    Information on the lateral spread of ions and/or damage is contained in the depth distribution normal to a target surface if ions are implanted into a tilted target. Following this principle the lateral spread of the carrier removal distribution formed by 300‐, 400‐, and 500‐keV proton implants in GaAs is evaluated from the several depth distributions of carrier removal which are formed by implants with different tilting angles and measured by the Copeland method. It is found that the lateral spread of carrier removal is largest at a depth near the projected range of protons. For instance the removal rate drops to 10% of its maximum value at about 0.7 μ laterally from a mask edge for 400‐keV protons for which the projected range is about 3.3 μ. It is also found that the lateral spread increases as the incident energy increases but that the ratio of the lateral to the longitudinal spreads decreases. View full abstract»

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  • A study of the lattice imperfections in Li‐diffused GaAs by transmission electron microscopy

    Page(s): 2784 - 2794
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    The lattice imperfections in GaAs single crystals introduced as a result of the in‐diffusion of lithium at high temperatures were investigated by using transmission electron microscopy. The effects of diffusion temperature, time, postdiffusion annealing treatments, and the presence of other impurities (primarily Zn at concentration levels of 1×1019 cm-3) in the host crystal, on the defect structure have been determined. The results indicate that when Li‐saturated GaAs single crystals are cooled to room temperature following high‐temperature diffusion, precipitation of Li occurs readily in the form of tetrahedral particles, the size and density of which decrease with decreases in diffusion temperature. Postdiffusion annealing at temperatures of 600 °C and above caused the formation of additional precipitates, vacancy‐type prismatic dislocation loops, and a few extrinsic stacking faults. Diffusion of Li into originally Zn‐doped GaAs ([Zn]∼1×1019 cm-3) at 700 °C, on the other hand, did not lead to the formation of Li precipitates; however, a moderately high density of small vacancy‐type prismatic loops was observed in the microstructure. On increasing the diffusion temperature to 850 °C the substructure revealed the presence of stacking faults and a small density of precipitates in addition to a number of large vacancy‐type prismatic loops. The size density and distribution of these defects were found to be dependent on the diffusion time at 850 °C. The origins of the observed lattice defects have been discussed in the light of the previous localized‐vibrational‐mode (LVM) infrared spectroscopy measurements on materials with identical chemical composition and thermal history as in the present study. A definite correlation between the microstructural features and defect structure a- s determined by infrared absorption measurements was found to exist. View full abstract»

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  • Electron beam induced annealing of defects in GaAs

    Page(s): 2795 - 2803
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    It has recently been shown that minority‐carrier injection greatly increases the annealing rate of 1‐MeV electron damage in GaAs. Energy deposited during nonradiative recombination at the radiation damage defects has been shown by Kimerling and Lang to be responsible for this effect. We have confirmed this effect in experiments in which carrier injection was achieved by 15–45‐keV electron irradiation. The annealing process was monitored during irradiation by measurement of the charge collected at a p‐n junction within the material. Carrier lifetime improvements of 100% were observed, and could be produced at rates 100 times faster than those reported by Kimerling and Lang when focused electron beam annealing was employed. Dislocations were observed to act as sinks for the defects. Focused electron beam annealing was employed to ’’write’’ annealed patterns in GaAs. View full abstract»

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  • Formal aspects of the theory of the scattering of ultrasound by flaws in elastic materials

    Page(s): 2804 - 2811
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    An integral equation is used to derive formal expressions for the scattering of a plane wave from a single homogeneous flaw embedded in an isotropic elastic medium. Expressions are found for the scattered amplitudes and differential cross sections. An optical theorem is also derived. View full abstract»

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  • The Born approximation in the theory of the scattering of elastic waves by flaws

    Page(s): 2812 - 2819
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    We used the integral equation formulation of the scattering of elastic waves to generate an approximate solution analogous to the Born approximation in quantum mechanics. This solution is attractive because of the ease with which it may be applied to scatterers of complicated shapes. We investigated the validity of the approximation by comparing it with exact results for spherical scatterers. Our conclusion for voids in elastic media is that the approximation describes well the scattering when the wavelength of the incident wave is approximately an order of magnitude larger than the scatterer and when the scattering is viewed in the backscattered directions. For many applications this range of validity is experimentally accessible. For elastic inclusions, however, where the properties of defect and host differed by 20–40%, the Born approximation is surprisingly good for all angles and even at short wavelengths. View full abstract»

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Aims & Scope

Journal of Applied Physics is the American Institute of Physics' (AIP) archival journal for significant new results in applied physics

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Editor
P. James Viccaro
Argonne National Laboratory