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  • Articles: DFG German National Licenses  (13)
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  • Articles: DFG German National Licenses  (13)
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  • 1
    Electronic Resource
    Electronic Resource
    Study of the gamma emission from the 31-yr isomer of 178Hf induced by x-ray irradiation (2000)
    Springer
    Physics of atomic nuclei 63 (2000), S. 2067-2072 
    Details
    ISSN: 1063-7788
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1134/1.1333875
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    Paper (German National Licenses)
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  • 2
    Electronic Resource
    Electronic Resource
    Study of two-body and three-body channels for the reaction of metastable helium atoms with selected atomic and molecular species (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 3061-3071 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This work reports the measurements of rate coefficients for excitation transfer reactions of metastable He(2 3S) atoms, produced in 0.3–4 atm of helium, with various reactants presenting a wide range of characteristics. In all cases studied, three-body reaction channels were identified with most probable values of rate coefficients lying in the range from 0.2 to 6.7×10−31 cm6 s−1, for Ne and N2O, respectively. These are generally more than one order of magnitude smaller than previously reported. The interpretation of this discrepancy in terms of a more reactive intermediate He2(Σ*) complex in dynamic equilibrium with the He(2 3S) population seems to be confirmed, and is analyzed in some detail.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453949
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Spectroscopic study of the afterglow excited by intense electrical discharges in high-pressure helium hydrogen mixtures (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 1095-1100 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In this work, we report the study of afterglow plasmas with initial electron density over 1015 cm−3 excited by repetitive 3 kA, 7 ns duration discharges in He–H2 mixtures with helium pressure in the range 310–760 Torr and partial pressure of hydrogen from 20 to 400 mTorr. The afterglow radiation was emitted in He2 transitions as well as in atomic hydrogen spectral lines, with Lα being particularly intense. The ground state H concentration was estimated from the profile of the self-absorbed Lα line, indicating that dissociation of hydrogen occurs mainly in the afterglow by electron–ion recombination. He (2 3S) destruction frequencies have been determined from measurements of the optical absorption of the 2 3S→3 3P helium transition and were analyzed in terms of rate coefficients for various quenching processes. Among these, the Penning reaction with atomic hydrogen was found to be important.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.449856
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    Paper (German National Licenses)
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  • 4
    Electronic Resource
    Electronic Resource
    Study of two-body and three-body channels for the reaction of metastable helium atoms with nitrogen (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 2274-2279 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: This work reports the characterization of late time periods in the decay of metastable He(2 3S) atoms produced in 1–4 atm of helium containing up to 1400 mTorr of N2. Results have been obtained that exploit the large dynamic range and high data acquisition rates available from time resolved spectroscopic studies of preionized stripline discharges. A new value was found for the termolecular reaction of (2 3S) with N2 of 1.5×10−31 cm6 s−1 that is in good agreement with a model of collisionally induced capture. An indirect channel of reaction was also found that seems to explain the anomalously rapid and conflicting termolecular rates that were previously reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448322
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  • 5
    Electronic Resource
    Electronic Resource
    Study of a fast ablative capillary discharge dedicated to soft x-ray production (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 15-19 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A capillary discharge has been developed to produce pulses of intense soft x-ray radiation of tens of nanoseconds duration. The soft x-ray photons were emitted in a plasma column resulting from polyethylene in capillary wall ablation. The spectrum was dominated by the C IV, C V, and C VI emission lines in the soft x-ray spectral range. The experimental value of the electrical circuit inductance has been measured and compared to the calculated one. The electron temperature was estimated to be higher than 50 eV from the plasma resistivity measurement. The time dependence of the electron density outside the capillary channel has been determined using spectroscopic measurement in the visible range. The time dependence of the electron temperature has been determined from the intensity ratio of C V and C VI emission lines, using a collisional radiative equilibrium code. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1150152
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  • 6
    Electronic Resource
    Electronic Resource
    Reactions of He(2 3S) with argon at atmospheric pressures (1986)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 85 (1986), S. 2338-2340 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.451084
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    Paper (German National Licenses)
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  • 7
    Electronic Resource
    Electronic Resource
    Theoretical study of the Rydberg excited electronic states of Ar+2 (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 6093-6103 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The first Rydberg states of the Ar+2 molecular ion dissociating into Ar+(3p5,2P) +Ar*(3p54s,3,1P) are calculated using multireference configuration interaction and effective core pseudopotentials. At long internuclear distance, their electronic structure is shown to be determined by resonance interaction and the magnitude of the Rydberg electron-transfer integral, inducing long-distance wells with De in the range 0.6–0.8 eV around Re(approximately-equal-to)9.0a0. In the short distance range, the electronic structure can be understood as resulting from an ionic Ar++ core with an outer Rydberg electron, and bound or quasibound Rydberg states are obtained around Re∼4a0. The fluorescence spectra of those states are simulated and the possible intervention of the Ar+2 system in the third continuum spectrum is considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462651
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  • 8
    Electronic Resource
    Electronic Resource
    Theoretical study of the electronic structure of Ar++2 (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 6085-6092 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electronic states of the ionic excimer Ar++2 are calculated using ab initio multireference configuration interaction and effective core pseudopotentials. Among states dissociating into Ar+(2P)+Ar+(2P), all are found to be repulsive, except the ground state, which occurs to be quasibound near Re=4.1a0 with a well depth of ≥230 cm−1. All states originating from Ar++(3P,1D,1S)+Ar are bound with dissociation energies in the range 3200–4500 cm−1 and equilibrium distances between 5.6a0 and 6a0. Simulation emission spectra from bound excited states are derived from the calculated potentials and the possible contribution of the Ar++2 ion to the third continuum fluorescence is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.462650
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    Paper (German National Licenses)
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  • 9
    Electronic Resource
    Electronic Resource
    Compact flash x-ray source producing high average powers in nanosecond pulses (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 2320-2325 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: X-ray diodes driven by repetitively pulsed Blumleins have been shown to be able to deliver high dose rates of x rays in pulses of nanosecond duration. Reported here is a study of the scaling of such devices conducted to isolate the primary factors limiting performance. Low residual gas pressure in the output diode together with the critical alignment of the electrodes were found essential for enhanced output. Optimizations served to increase the x-ray yield by an order of magnitude and the resulting performance is reported. At the output window, dose rates exceeding 1.4 kR min−1 were obtained in nanosecond pulses from the finished device of table top size at a charging voltage of 30 kV and a pulse repetition rate of 50 Hz.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1143928
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  • 10
    Electronic Resource
    Electronic Resource
    High repetition rate compact source of nanosecond pulses of 5–100 keV x-ray photons (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 2292-2297 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A powerful, compact, and repetitive flash x-ray system based on a cable transformer technology powered by ceramic capacitors in a Blumlein-like configuration has been developed. Open circuit voltages in excess of 100 kV can be achieved while commutation occurs at low voltage (〈20 kV). The x-ray emission from a low impedance x-ray diode with a hollow cathode configuration was observed under a wide range of experimental conditions. The critical parameters limiting the flash x-ray performances are mainly the pressure in the x-ray diode and the anode–cathode space. This true table top device is able to produce doses up to 1 R per shot, measured at the output window, of x-rays between 5 and 100 keV. The pulse widths were about 20 ns and the maximum repetition rate was about 60 Hz. Operation is possible in air or in other gases (He, Ne, Ar, Kr, Xe, H2, N2) at pressures varying from 10−3 mbar for xenon to about 1 mbar for helium. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148137
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