ns1

Information about ns1

Published on October 13, 2007

Author: Alohomora

Source: authorstream.com

Content

Inhalt:  Einführung in die Neutronenstreuung Dr. M. Rotter, Inst. f. Phys. Chemie, Zi 2245 [email protected] Tel. 4277 52469 Materialchemie VI,Vorlesung SS 2003, 2 Wst Wahlfach Materialchemie, anrechenbar für Wahlfach physikalische Chemie Institut f. Physikalische Chemie  der Universität Wien Das Neutron: Erzeugung,Eigenschaften Streutheorie, Wechselwirkungsmechanismen Van Hove Streufunktion Neutronendiffraktometrie – Kernstreuung, koherente-inkoherente Streuung Magnetische Strukturbestimmung Phononen, Kristallfelder „Linear Response“ Theorie, dynamische Suszeptibilität „Random Phase Approximation“ 7. Phononen-Spektroskopie Magnetische Anregungen Numerische Methoden zur Datenanalyse Polarisierte Neutronen Neutronen-Spin Echo Technik Kleinwinkelstreuung Inhalt Termine Blocklehrveranstaltung n.Ü. Zeit: Mo, Do 9-11h Ort: Seminarraum des Instituts für Physikalische Chemie Nobelpreise:  Nobelpreise "for pioneering contributions to the development of neutron scattering techniques for studies of condensed matter" "for the development of neutron spectroscopy" "for the development of the neutron diffraction technique" The Nobel Prize in Physics 1935 "for the discovery of the neutron" "In simple terms, Clifford G. Shull has helped answer the question of where atoms are, and Bertram N. Brockhouse the question of what atoms do“, (Nobel citation) James Chadwick 1932: Entdeckung von Chadwick:  1932: Entdeckung von Chadwick 212Po208Pb+α 9Be+ α 12C+n verschiedene Absorber (Paraffin (H), He, Li) Ionisationskammer Neutrons:  Neutrons Mn = 1.674928.10-27kg = 1.001 MProton τ = 885 s (β decay) n  p + e-+νe+0.78MeV n: E=h2/2Mnλ2=81.1meV/λ2 photon: E=hf=hc/λ=12398eV/ λ k=2π/ λ p=h/ λ units: 1 meV=11.6 K=8.066/cm=0.241THz λ[Å] k[1/Å] v(m/s) E best ΔE/E Photon light 5000 10-3 3.108 eV 10-8 X-ray 1 1 3.108 keV 10-6 electron 1 1 6.107 150eV 10-5 neutron 1 1 400 meV 10-6 Eigenschaften:  Eigenschaften Ladung=0 elektr. Dipolmoment=0 Spin: S = 1/2 magnetisches Dipolmoment: μ = 9.6491783.10-27J/T = -1.913042 μN μN=μB me/mp=0.5446 10-3μB „Erklärung“: DIRAC μProton=1 μN exp 2.8 μN μNeutron=0 exp –1.9 μN MESON p  n + π+ n  p + π- μNeutron0: Neutron ist 20% der Zeit p+π-, wobei π- Bahnmoment von 10 μN hat. QUARK u d d Reaktor-Neutronenquellen:  Reaktor-Neutronenquellen ILL, Grenoble,F U235+n  Mo95+La139+2n 235x7.6 95x8.6 138x8.4MeV i.e. 200MeV freiwerdende Energie Davon 6MeV kin Energie der n Slide7:  FRM-II - thermal power: 20MW ILL: 56MW unperturbed thermal neutron flux: 8x1014cm-2s-1 core cooled with light water H20 moderator tank: heavy water D20 diameter of approx. 2,5m Slide8:  FRM-II's reactor core: a single, cylindrical fuel element 700mm height. 113 involuted, curved fuel plates three layers: fuel U3Si2 + aluminium powder in an aluminium matrix. 5 elements will be required per year. Thermal neutron flux density as function of the radius (FRM-II) Spallation:  Spallation pro freigesetztem Neutron entsteht bei der Spallation weniger Wärme als bei der Kettenreaktion .... daher sind höhere Flüsse möglich: spitzenwerte thermische Neutronen 2x1017n/cm2s (geplant bei der ESS) Pb: 20n/p +23MeV 238U: 40n/p +50MeV (vgl 235U:1n/spaltung + 200MeV) Spallations-Neutronenquellen:  Spallations-Neutronenquellen ISIS, Oxford, UK In Planung Slide11:  Austron, A SNS, Oakridge, USA In Bau In Planung 1.500.000€ 700.000€ 1.400.000$ Reactor-Sources Spallation Sources:  Reactor-Sources Spallation Sources Budapest Neutron Centre, AEKI, Budapest, Hungary  Berlin Neutron Scattering Center, Hahn-Meitner-Institut, Berlin  Center for Fundamental and Applied Neutron Research (CFANR), Rez nr Prague, Czech Republic  FRJ-2 Reactor, Forschungzentrum Jülich, Germany  Frank Laboratory of Neutron Physics, Joint Institute of Nuclear Research, Dubna, Russia  GKSS Institute for Materials Research, Hamburg, Germany  Institut Laue Langevin, Grenoble, France  Interfacultair Reactor Instituut, Delft University of Technology, NL JEEP-II Reactor, IFE, Kjeller, Norway  Laboratoire Léon Brillouin, Saclay, France  Ljubljana TRIGA MARK II Research Reactor, J. Stefan Institute, Slovenia  St. Petersburg Nuclear Physics Institute, Gatchina, Russia  Studsvik Neutron Research Laboratory (NFL), Studsvik, Sweden  Centro Atomico Bariloche, Rio Negro, Argentina  Chalk River Neutron Program for Material Research, Chalk River, Ontario, Canada  High Flux Isotope Reactor (HFIR), Oak Ridge National Laboratory, Tennessee, USA  Los Alamos Neutron Science Center (LANSCE), New Mexico, USA  McMaster Nuclear Reactor, Hamilton, Ontario, Canada  MIT Nuclear Reactor Laboratory, Massachusetts, USA  NIST Center for Neutron Research, Gaithersburg, Maryland, USA  Peruvian Institute of Nuclear Energy (IPEN), Lima, Peru  University of Missouri Research Reactor, Columbia, Missouri, USA  University of Illinois Triga Reactor, Urbana-Champaign, Illinois, USA Institute, Australian Nuclear Science and Technology Organisation, Lucas Heights, Australia  High-flux Advanced Neutron Application Reactor (HANARO), Korea  Japan Atomic Energy Research Institute (JAERI), Tokai, Japan  KENS Neutron Scattering Facility, KEK, Tsukuba, Japan  Kyoto University Research Reactor Institute (KURRI), Kyoto, Japan  Malaysian Institute for Nuclear Technology Research (MINT), Malaysia  Australian Replacement Research Reactor, Lucas Heights, Australia  Canadian Neutron Facility, Chalk River, Ontario, Canada  FRM-II Research Reactor, Garching, Germany  ISIS Pulsed Neutron Facility, Rutherford-Appleton Laboratory, Oxfordshire, UK  Swiss Spallation Neutron Source (SINQ), Villigen SwitzerlandBragg Intense Pulsed Neutron Source (IPNS), Argonne National Laboratory, Illinois, USA  Spallation Neutron Source, Oak Ridge National Laboratory, Tennessee, USA Austron Spallation Neutron Source, Vienna, Austria  European Spallation Source (ESS)  Japan Proton Accelerator Research Complex (J-PARC), Tokai, Japan  Wechselwirkung mit Materie:  Wechselwirkung mit Materie Schwächungskoeffizienten Σ:  Schwächungskoeffizienten Σ (Energy – Dependence):  (Energy – Dependence) Moderatoren (D2O) :  Moderatoren (D2O) MeVmeV durch elastische Streuung an leichten Elementen verlieren die Neutronen Energie und es ergibt sich im Idealfall eine Maxwell Verteilung der n-Geschwindigkeit entsprechend der Moderator Temperatur Betrachtung eines elastischen Stoßes eines Neutrons mit einem Kern der Massenzahl A ergibt: Am besten wäre Wasserstoff Problem - Absorption - daher Deuterium ! 25K 3000K (Graphit) 300K Berechnung für FRM-II, Garching Beispiel 1::  Beispiel 1: Wieviel cm verliert ein Neutron an Höhe infolge der Gravitation, wenn es ein Strahlrohr von 30m Länge passiert ? Vergleich: Neutronen aus einer kalten Quelle (4K,25K), thermische Neutronen (300K) und aus einer heißen Quelle (3000K) Nachweis von Neutronen:  Nachweis von Neutronen n nicht ionisierend – daher immer indirekter Nachweis (keine Energieanalyse bei Nachweis) schnelle Neutronen (MeV): Stöße mit p-haltigen Substanzen thermische Neutronen (meV): Aktivierung durch n – Einfang (z.B. n-γ Reaktionen in Au,In) 2. Kernreaktionen und anschließender Nachweis der (geladenen) Reaktions produkte – üblich in der Neutronenstreuung: Geiger Müller Zählrohr a) BF3: B10 (n, α) Li7 + 2.79MeV b) He3: He3 (n,p) H3 + 0.765MeV Nachweiswahrscheinlichkeiten ca 95% (hängt von λ ab, λ 1/v) 3. Szintillationszähler: n  B  α ZnS (Photomultiplier) Das Streuexperiment:  Das Streuexperiment Wirkungsquerschnitte Total Differentiell Doppelt Differentiell Streugesetz S .... Streufunktion Einheit: 1 barn=10-28 m2 (ca. Kernradius2) Energie/Impulsübertrag:  Energie/Impulsübertrag Neutron – Photon Streuquerschnitte :  Neutron – Photon Streuquerschnitte Neutrons – Photons:  Neutrons – Photons  Neutrons: Particle beam (neutral) E=h2/2mNλ2=81.1meV/λ2 Low brilliance (particles/cm2/sr/meV) Interactions with the nuclei and the magnetic moment of unpaired electrons Scattered by all elements, also the light ones like the hydrogen isotopes Deep penetration depth (bulk studies of samples) Less intense beam measuring larger samples   Applications: Magnetic structures & excitations, critical scattering     Photons: Light beam E=hf=hc/λ=12398eV/ λ High brilliance Interactions with the electrons surrounding the nuclei Mainly scattered by heavy elements   Small penetration depth (surface studies of samples) Very intense beam measuring small or ultra-dilute samples Applications: Surface studies, element and shell sensitive resonant magnetic scattering, magnetic dichroism, magnetic Materials with high neutron absorption Literatur:  Literatur S. W. Lovesey Theory of Neutron Scattering from Oxford (1981) Condensed Matter G. E. Bacon Neutron Physics Wykeham (1969) G. E. Bacon Neutron Diffraction Oxford (1979) Izyumov, Ozerov Magnetic Neutron Diffraction Plenum (1970) J. Jensen Rare Earth Magnetism Oxford (1991) Oxford Series on Neutron Scattering in Condensed Matter Volume 1.-12.

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