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  • acceptance-rejection  (2)
  • 12.38.Qk Experimental tests  (1)
  • 25.85.Jg  (1)
  • 29.25  (1)
  • 1
    Digitale Medien
    Digitale Medien
    Intense source of slow positrons from pulsed electron accelerators (1984)
    Springer
    Applied physics 33 (1984), S. 59-62 
    Details
    ISSN: 1432-0630
    Schlagwort(e): 7.77 ; 29.25
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Maschinenbau , Physik
    Notizen: Abstract A pulsed LINAC is used for pair production in a tantalum target of 2.5 radiation lengths in an energy range from 80 to 260 MeV. Several well-annealed tungsten vanes are placed immediately behind the target and thermalize a small fraction of the fast positrons. The slow positrons are extracted from the target region and magnetically guided over a distance of 17 m to the detector at the end of an S-shaped solenoid. Two Nal detectors with well-known detection efficiency are used to register the 511 keV annihilationγ-rays. To reduce pile-up effects 50 mm of Pb were placed in front of the detectors. At an average electron current of 1 μA we could detect about 107 slow positrons per second. The positron yield is proportional to the electron current, and shows an increase with the electron energy for our target. The positron energy distribution has a FWHM of ∼ 1.8 eV.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01197087
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    A one-table method for sampling from continuous and discrete distributions (1995)
    Springer
    Computing 54 (1995), S. 127-146 
    Details
    ISSN: 1436-5057
    Schlagwort(e): 65C10 ; 65C05 ; Random number generation ; table method ; acceptance-rejection
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Für die Erzeugung von Stichproben aus weitgehend beliebigen VerteilungenF mit Dichtefunktionenf(x) oder Wahrscheinlichkeitenp k (in diskreten Fällen) wird eine praxisnahe Methode entwickelt. Die hohe Effizienz der Stichprobengewinnung wird mittels einer einzigen Hilfstafel erreicht, die eine Unterteilung des Bereiches vonF enthält. Beispiele stetiger und diskreter Verteilungen zeigen, daß die Prozedur einfach zu handhaben ist und daß ihre Geschwindigkeit nicht sehr von der speziellen VerteilungF abhängt.
    Notizen: Abstract A practical method for sampling from largely arbitrary distributionsF with density functionsf(x) or probabilitiesp k (in discrete cases) is developed. The high efficiency of the sampling routine is achieved by means of only one auxiliary table which contains a subdivision of the range ofF. Examples of continuous and discrete distributions demonstrate that the procedure is easy to apply and that its speed does not much depend on the particular target distributionF.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02238128
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  • 3
    Digitale Medien
    Digitale Medien
    Photofission of235U and238U at intermediate energies: absolute cross sections and fragment mass distributions (1994)
    Springer
    The European physical journal 350 (1994), S. 249-261 
    Details
    ISSN: 1434-601X
    Schlagwort(e): 25.20.Dc ; 25.85.Jg ; 27.90.+b
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract The total photofission cross section σγ,F for235U and238U has been measured in the energy range 50≤E γ≤800 MeV at the 855 MeV Mainz Microtron MAMI using energy and time tagged photons (Glasgow Tagger) and a 4π arrangement of position sensitive fragment detectors. Besides the absolute photofission cross section σγF , which almost completely exhausts the total photon absorption cross section for these nuclei, fragment mass distributions in this energy domain were determined via time of flight techniques (TOF). The results for the total photofission cross sections σγ,F normalized to the atomic numberA for both isotopes coincide, and agree in theΔ-resonance region, within the systematic errors, with the socalled“Universal Curve” σγ,T /A of the total photon absorption cross section σγ,T . At higher energies the cross sections exhibit a smooth behaviour. In particular, it is shown for the first time that there isno resonance-like shape near the D13 resonance (at ≈710 MeV) as observed for the free proton. This complete suppression of the D13 resonance in complex nuclei is not yet understood on a microscopic level. The fragment mass distributions show a predominantly mass symmetric fission. However, contributions from mass asymmetric fission at some photon energies may give a hint of an increased mass asymmetric fission after the onset of the pion and two pion channels.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF01289589
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  • 4
    Digitale Medien
    Digitale Medien
    How to avoid logarithms in comparisons with uniform random variables (1989)
    Springer
    Computing 41 (1989), S. 163-166 
    Details
    ISSN: 1436-5057
    Schlagwort(e): Primary 65 C 10 ; Random variables ; acceptance-rejection ; logarithm
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Informatik
    Beschreibung / Inhaltsverzeichnis: Zusammenfassung Bei der Erzeugung nicht-gleichverteilter Zufallszahlen muß häufig der Logarithmus einer gleichverteilten Zufallszahl mit einer Testgröße verglichen werden. Es wird gezeigt, daß dieser Vergleich ohne den Aufruf einer Logarithmusroutine effizient durchführbar ist; zwei Prozeduren für diese Aufgabe werden vorgestellt und verglichen.
    Notizen: Abstract In many algorithms for sampling from non-uniform distributions the logarithm of a uniform deviate must be compared with some test quantity. It is shown that all these comparisons can be done efficiently without calling a logarithm subprogram: two procedures for this task are presented and compared.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1007/BF02238740
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  • 5
    Digitale Medien
    Digitale Medien
    Measurement of the πmeson polarizabilities via the γp → γπ+n reaction (2005)
    Springer
    The European physical journal 23 (2005), S. 113-127 
    Details
    ISSN: 1434-601X
    Schlagwort(e): 12.38.Qk Experimental tests ; 13.40.-f Electromagnetic processes and properties ; 13.60.Le Meson production
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract. An experiment on the radiative π{+}-meson photoproduction from the proton ( γp → γπ{+}n) was carried out at the Mainz Microtron MAMI in the kinematic region 537MeV 〈 Eγ 〈 817MeV, 140°≤ $ \theta_{{\gamma \gamma ^{\prime }}}^{{{{\rm cm}}}}$ ≤180°. The π{+}-meson polarizabilities have been determined from a comparison of the data with the predictions of two different theoretical models, the first one being based on an effective pole model with pseudoscalar coupling while the second one is based on diagrams describing both resonant and nonresonant contributions. The validity of the models has been verified by comparing the predictions with the present experimental data in the kinematic region where the pion polarizability contribution is negligible ( s1 〈 5mπ2) and where the difference between the predictions of the two models does not exceed 3%. In the region, where the pion polarizability contribution is substantial ( 5 〈 s1/mπ2 〈 15, -12 〈 t/mπ2 〈 - 2), the difference $\ensuremath{(\alpha -\beta )_{\pi^{+}}}$ of the electric (α) and the magnetic (β) polarizabilities has been determined. As a result we find $\ensuremath{(\alpha -\beta )_{\pi^{+}}=(11.6\pm 1.5_{{\rm stat}}\pm 3.0_{{\rm syst}}\pm 0.5_{{\rm mod}})\times 10^{-4}{}{\rm fm^{3}}}$ . This result is at variance with recent calculations in the framework of chiral perturbation theory.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1140/epja/i2004-10056-2
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