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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3247-3253 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A prototype monolithic capillary lens for focusing neutrons produced by thermally drawing straight multicapillary bundles has been characterized with cold neutrons, and gives an intensity gain of a factor of 25 at a focal distance of 8 mm, over the focal spot area of width 87 μm. This is over an order of magnitude smaller in area than for the multifiber capillary lens. The spatial resolution available with the lens has been tested with prompt gamma measurements on slivers of dysprosium. Background problems that can affect the spatial resolution of measurements taken at the focal position of the lens are addressed. The boron glass of the tapered monolithic lens provides good shielding from unfocused neutrons in the vicinity of the lens focus. © 2000 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 67 (1996), S. 2770-2774 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A very small Fermi-type neutron chopper fashioned by cutting slots in a boron nitride cylinder was developed for use with a source of thermal and cold (subthermal velocity) neutrons. The original goal was to characterize spectra emerging from glass capillary fibers of less than 1 mm diameter, but other applications became apparent. For approximately 1 m flight paths, conventional nuclear electronics had to be adapted to the millisecond flight times. Both time-to-amplitude converter and multiscaling time-data storage methods were used. Data corrections for the particular geometry are reviewed and applied to the present geometry. Among examples of its potential use, the spectrum of a newly installed cold source was measured. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 3399-3402 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A neutron lens constructed with polycapillary glass fibers is used to focus a 50×45 mm2 beam exiting a cold neutron guide onto a spot of 0.53 mm (full width at half maximum) with a current density gain of 80. The characteristics of the lens are presented. This lens is designed to enhance the detection limit and lateral resolution for prompt gamma activation analysis using cold neutron beams.
    Materialart: Digitale Medien
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  • 4
    Digitale Medien
    Digitale Medien
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 71 (1997), S. 3168-3170 
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The cold neutron transmission through a monolithic polycapillary lens is studied by scanning a pinhole beam across the entrance cross section of the lens. The relative transmission as a function of bending radius of a tapered channel is obtained. The results are explained in terms of a reduced critical angle for total reflection for the tapered channels. A technique for qualitative examination of monolithic lenses is proposed. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 33 (2000), S. 1253-1261 
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: Small-angle neutron scattering (SANS) measurements have been performed on long-flight-path pinhole-collimation SANS instruments using, as a two-dimensional position-sensitive detector, both a neutron imaging plate, incorporating gadolinium, and a two-step transfer method, with dysprosium foil as the image transfer medium. The measurements are compared with corresponding data taken using conventional position-sensitive gas proportional counters on the SANS instruments in order to assess the viability of the imaging techniques. The imaging plates have pixel sizes of about two orders of magnitude smaller than those of the gas proportional counter. The reduced pixel size provides definite advantages over the gas counter in certain specific situations, namely when limited space necessitates a short sample-to-detector distance, when only small samples (comparable in size to the detector pixels) are available, or when used in conjunction with focusing beam optics.
    Materialart: Digitale Medien
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  • 6
    Digitale Medien
    Digitale Medien
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 28 (1995), S. 69-77 
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: The average number of reflections for radiation transmitted by a straight cylindrical channel can be determined analytically for an input beam for which the divergence has polar symmetry. For the case of an incident beam with a divergence of Cartesian symmetry (for example, the output from a rectangular neutron guide), the number of reflections can be calculated only if the maximum divergence is less than the critical angle of the cylindrical channel. For larger divergences, the requirement that the glacing angle is less than the critical angle does not allow a simple analytic solution. This paper reports the calculation of the number of reflections using an approximation and makes comparisons with a numerical simulation that gives an estimate of the exact result.
    Materialart: Digitale Medien
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  • 7
    Digitale Medien
    Digitale Medien
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 30 (1997), S. 324-326 
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: The fraction of trajectories that have a given number of reflections during the passage of a neutron beam through a long cylindrical channel is determined when the angular divergence of the incident beam is less than the critical angle of the inner surface of the channel. This is useful for estimating the reflectivity from neutron-transmission measurements. The results are shown on a universal curve.
    Materialart: Digitale Medien
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  • 8
    Digitale Medien
    Digitale Medien
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 30 (1997), S. 932-942 
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: The transmission of neutrons through a tapered channel is analyzed and the relationships among various parameters such as the distance between reflections and the polar and grazing angles of a trajectory at each reflection are established. These relationships are used in a simulation to study the transmission characteristics of a cylindrical tapered channel. The transmission, the transmitted beam angular divergence and the number of reflections are determined for different values of the taper angle and the incident beam divergence. The simulation results for the straight channel agree exactly with the derived analytical expressions. Those for the tapered channels can be described using the same expressions but with a lower effective critical angle. This reduced critical angle depends on the length of the taper and on the taper angle. For long gentle tapers, the reduction in critical angle is equal to the reduction in channel diameter.
    Materialart: Digitale Medien
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  • 9
    Digitale Medien
    Digitale Medien
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 28 (1995), S. 793-802 
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: The transmission and the number of reflections of successful neutron trajectories through a straight cylindrical tube with a coaxial aperture at its entrance have been calculated, assuming that a beam with a conical angular divergence is incident along the axis of the cylinder. The calculation models neutron transmission measurements through tubes that have been defined by a cadmium aperture placed at the entrance of the tube. The addition of an aperture not only lowers the acceptance, but also reduces the average number of reflections relative to unrestricted transmission. The aperture prevents neutrons having trajectories with tight spirals down the tube from entering near the periphery of the tube. This model might also be useful for understanding the reduced transmission through a tube with slightly crimped edges or through imperfectly cut glass polycapillaries.
    Materialart: Digitale Medien
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  • 10
    Digitale Medien
    Digitale Medien
    [s.l.] : Nature Publishing Group
    Nature 357 (1992), S. 390-391 
    ISSN: 1476-4687
    Quelle: Nature Archives 1869 - 2009
    Thema: Biologie , Chemie und Pharmazie , Medizin , Allgemeine Naturwissenschaft , Physik
    Notizen: [Auszug] Using a steering device to make the neutron flux more intense and localized improves both spatial resolution and detection limits in applications of thermal and cold neutrons to materials analysis. This also increases the efficiency of neutron capture therapy and reduces ...
    Materialart: Digitale Medien
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