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  • 1
    ISSN: 1063-7788
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract A sample containing 6.3×1014 nuclei of the 16+ isomer of 178Hf having a half-life of 31 yr and an excitation energy of 2.446 MeV was irradiated with x-ray pulses from a device operated at 15 mA to produce bremsstrahlung with an endpoint energy of 90 keV. The gamma spectra of the isomeric target were taken with a Ge detector. The intensity of the 325.5-keV (6+ → 4+) transition in the ground-state band of 178Hf was found to increase by about 2%. Such an enhanced decay of the 178Hf isomer is consistent with an integrated cross section value of 3×10−23 cm2 keV if resonance absorption occurs within energy ranges corresponding to the maxima of the x-ray flux, either near 20 keV or at the energies of the characteristic emission lines of W.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 4965-4976 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: This report belongs to a series concerned with the correlation of photolysis bands observed in electronic transition spectra of simple molecules with their dissociation products. In this work a time-delayed, double resonance application of optical impedance spectroscopy was used for the study of the state selective photolysis of Cs2 excited in the yellow range of visible wavelengths. Two independently tunable dye lasers were synchronously pulsed, the first being used to dissociate the constituents of the sample along the various possible channels and the second, delayed pulse being used to identify the products by exciting them selectively into easily detected Rydberg states. The time between photolysis and detection could be varied, starting from a value too short to permit collisional mixing or radiative cascading of the products. Particular attention was paid to the photolytic production of the fine structure components of the first and second electronically excited state of atomic cesium and to the subsequent processes which tended to degrade the selectivity produced in the initial distributions of product populations among the available states. Data were fit to a quantitative model from which rate coefficients could be extracted for various mixing processes. Reported here is what appears to be a first value for the fine-structure mixing cross section (5 2D5/2→5 2D3/2) of 17 A(ring)2±60%. In addition a delayed process for the selective production of Cs(5 2D) atoms was found to result from the excitation of a state having a lifetime less than 100 ns that is tentatively identified as a molecular state correlated with Cs(5 2D), possibly 5d 3Δu.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 2260-2264 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Eight triaxial Blumleins have been stacked in series at one end while being synchronously commuted at the other end with a single hydrogen thyratron. Significant voltage gain has been maintained in the stack for periods of the order of 20 ns. Having no other switching elements, operation has been possible at repetition rates to 100 Hz. An x-ray diode has been matched to this pulse power source, making possible the emission of an average bremsstrahlung dose of 5.8 R/s from a sequence of 20-ns pulses. In less than 4 min of operation at 100 Hz, a dose of 1 kR could have been delivered to a target sample. When operated at 50-kV charging voltage, spectral measurements show the output to be a true continuum, peaking at intensities in excess of 2×108 keV/keV/shot and containing useful intensities of photons having energies of 150 keV.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 54 (1989), S. 216-218 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Amorphic diamond films characterized by a high percentage of sp3 bonds have been prepared in an UHV environment with a laser plasma source of carbon ions. Peak power densities in excess of 1011 W/cm2 were found necessary to produce films at growth rates of 0.5 μm/h over areas of 20 cm2 having optical quality sufficient to show bright interference colors.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 1446-1453 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Amorphic diamond films can be grown in an ultrahigh vacuum environment free from hydrogen with a laser plasma discharge source. This technique produces films that adhere more readily to materials for which there are important applications as protective coatings. In this work adhesion and mechanical properties of amorphic diamond films have been examined. A beam bending method has been used to measure the internal stress and a relatively low value of compressive stress was found. The dependence of stress on the laser intensities at the graphite ablation target has been studied. Analyses of these films on silicon, SiO2, ZnS, and TiAl6V4 by Rutherford backscattering spectrometry show significant interfacial layers with compositions of SiC, C0.5SiO2, C2.5ZnS, and C0.62Ti0.35Al0.05V0.02, respectively. Adhesion properties on ZnS and other substrates have also been examined for harsh environments. The mechanical properties of hardness, Young's modulus, and stiffness have been obtained with a nanoindentation technique. These results together with the minimal amount of hydrogen in our process, make amorphic diamond an excellent candidate for direct deposition on several substrates including ZnS.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 7862-7870 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: It has been previously reported that layers of amorphic diamond can be grown in a UHV environment free from hydrogen with a laser plasma source. Some advantages are offered by this technique which produces films that adhere more readily to materials for which there are important applications. Theory has recently suggested a structure for amorphic diamond that comprises nodules of carbon atoms linked by sp3 bonds in a matrix of other polytypes and the purpose of this article is to communicate strong evidence in support of that hypothesis. Extensive examinations of a variety of films with a scanning tunneling microscope show a clearly prevalent structure composed of dense nodules. Grain size is about 1000 A(ring) and the diamond character is attested by the agreement of morphology, high density, optical properties, soft x-ray spectroscopy, hardness, and lack of appreciable hydrogen. Measurements agree in supporting a fraction of about 75% diamond contents. The principal conclusion is that this material prepared with a laser plasma source has the structure expected for amorphic diamond.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 239-245 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Recent experiments have identified the microstructure of amorphic diamond with a model of packed nodules of amorphous diamond expected theoretically. However, this success has left in doubt the relationship of amorphic diamond to other noncrystalline forms of carbon. This work reports the comparative examinations of the microstructures of samples of amorphic diamond, i-C, and amorphous carbon. Four distinct morphologies were found that correlated closely with the energy densities used in preparing the different materials.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 3260-3265 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Films of amorphic diamond can be deposited from laser plasma ions without the use of catalysts such as hydrogen or fluorine. Prepared without columnar patterns of growth, the layers of this material have been reported to have "bulk'' values of mechanical properties that have suggested their usage as protective coatings for metals. Described here is a study of the bonding and properties realized in one such example, the deposition of amorphic diamond on titanium. Measurements with Rutherford backscattering spectrometry and transmission electron microscopy showed that the diamond coatings deposited from laser plasmas were chemically bonded to Ti substrates in 100–200-A(ring)-thick interfacial layers containing some crystalline precipitates of TiC. Resistance to wear was estimated with a modified sand blaster and in all cases the coating was worn away without any rupture or deterioration of the bonding layer. Such wear was greatly reduced and lifetimes of the coated samples were increased by a factor of better than 300 with only 2.7 μm of amorphic diamond.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 2081-2087 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Recently, attention has been focused upon laser plasma sources of thin-film diamond. These depend upon laser-ignited discharges in which intense pulsed currents flow through the small volume of carbon plasma ablated from graphite feedstock by a focused laser beam. The materials produced in this way generally resemble the hard amorphic films deposited by ion beams. This paper reports a detailed characterization of these films which we call amorphic diamond. The combination of an optical band gap of 1.0 eV with a grain size of 100–200 A(ring) places this material far outside the range of possibilities available to the model of graphitic islands. A structure of very fine grained diamond would more readily explain the hardness of 13 GPa determined in the absence of any measurable fraction of hydrogen. Such amorphic diamond films have been grown uniformly on 100-cm2 areas at ambient room temperatures with no seeding or abrasion of the substrate.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 58 (1987), S. 2103-2109 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Described here is the scaling of a repetitively pulsed, flash x-ray source to yield 140-mW average power in 15-ns pulses of radiation near 1 A(ring). Interchangeability of discharge anodes has provided for a significant fraction of the output to be extracted in the K lines of Cu, Mo, Nb, and Ag. In less than 1 min of experimental time, a peak spectral density is radiated that exceeds 1×1018 keV/keV. For some applications this device can offer a tabletop alternative to laser plasma x rays and to synchrotron radiation.
    Materialart: Digitale Medien
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