1 / 22

M ő ssbauer Spectroscopy

X Ray Detection &. M ő ssbauer Spectroscopy. Today’s Agenda. X Ray Spectroscopy Spectra Absorption Response of proportional c ounters to g and X rays Mössbauer Spectroscopy: Principle Technique Results. X Ray Energies. Conrad R ő ntgen Discovered X rays: Electron Transitions.

huey
Download Presentation

M ő ssbauer Spectroscopy

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. X Ray Detection & Mőssbauer Spectroscopy

  2. Today’s Agenda • X Ray Spectroscopy • Spectra • Absorption • Response of proportional counters to g and X rays • Mössbauer Spectroscopy: • Principle • Technique • Results W. Udo Schröder, 2012

  3. X Ray Energies Conrad Rőntgen Discovered X rays: Electron Transitions Conrad Rőntgen Photon Photon W. Udo Schröder, 2012

  4. Absorption of X Rays in Gases Low-energy X ray photons interact with matter dominantly via photo effect (ionization) mostly with K shell electrons. High-Z counting gas W. Udo Schröder, 2012

  5. Gas Counters Most commercial counters are permanently sealed. Exponential increase of signal amplitude with voltage. Moderate (10%) resolution, but economic counter. W. Udo Schröder, 2012

  6. Example: 57Co g-Rays Low-energy X rays: interact with matter dominantly via photo effect, mostly with K shell. K-hole migrates to higher atomic levels in cascade of additional electronic X ray transitions g X W. Udo Schröder, 2012

  7. Complex PC Response to Photons High-energy: 2p-1s, 3d-2p E1 transitions K-X ray energy missing from full-energy peak low-energy transitions absorbed X ray photons from recombination or Auger cascade can escape a “thin” detector  escape lines (remember escape lines for scintillation/SSD gamma detectors) Also: Wall effects. high-energy transition escape Kr: IE(K)=14.263 keV 2p-1s 12.6 keV 3d-2p 1.64 keV W. Udo Schröder, 2012

  8. The Mőssbauer Effect 1961 Nobel Prize in Physics. Discovered(1958) recoilless nuclear fluorescence of gamma rays in 191Ir. Famous application: proof of red shift of gamma radiation in the gravitational field of the earth (Robert Pound and Glen Rebka); Pound–Rebkaexperiment was one of the first experimental precision tests of Albert Einstein's theory of general relativity. Long-term importance: Use of Mössbauer effect in”Mössbauer spectroscopy” testing solid-state and chemical environments via electric and magnetic hyperfine interactions between atomic electrons and nuclear charge and magnetization distributions. Rudolf Mőssbauer W. Udo Schröder, 2012

  9. g Energy Shifts due to Nuclear Recoil W. Udo Schröder, 2012

  10. Resonant Emission/Absorption of g-Rays Quantum Effect: System absorbs electromagnetic radiation only if its energy hn can bridge system energy levels: and if one of the levels (i, k) is occupied.  Use for scanning level scheme {En} W. Udo Schröder, 2012

  11. The Mössbauer Experiment. • If the line width G is small, resonant absorption is unlikely. • Using the Doppler effect, one can shift the energy of the emitted g ray to an energy E(v) where it can be absorbed. • By measuring the shift(s) required for absorption one can scan the level structure of the absorber and/or the source. • High scan resolution for small G and precise v. Scan absorber spectrum via resonant absorption W. Udo Schröder, 2012

  12. Mőssbauer Experiment Setup Velocity Drive (Transducer)Source DriverController Be WindowThickness 23 mg/cm2 Absorber Be Window W. Udo Schröder, 2012

  13. Mössbauer Experiment: Selecting Transition 57Co57Fe W. Udo Schröder, 2012

  14. r(r) rN(r) r Isomer (Chemical) Shift Coulomb potential for spatially extended nucleus  depends on R Point Nucleus Finite Size Nucleus R Perturbation theory calculation of energy level, perturbation=H’ Transmission of g-ray through absorber depends on source velocity W. Udo Schröder, 2012

  15. Electric Quadrupole HF Interaction Nuclear electric quadrupole moment eQ measures deviation from sphere. W. Udo Schröder, 2012

  16. Magnetic HF Interaction gN = Gyro-magnetic ratio= nuclear property different for different nucleonic configurations  structure info! Fe is ferromagnetic  magnetic HF splitting W. Udo Schröder, 2012

  17. Electric + Magnetic HF Interactions Isomer-shifted Fe hyperfine level scheme and allowed E1 transitions Mössbauer velocity absorption spectra are shifted against zero and split W. Udo Schröder, 2012

  18. The End W. Udo Schröder, 2012

  19. Magnetic Hyperfine Splitting W. Udo Schröder, 2012

  20. Probing Ordinary Iron W. Udo Schröder, 2012

  21. gas Rc signal + - C R - U0 + RI RA eUIRI Anode Wire e- q+ Proportional Counter Anode wire: small radius RA ≈ 50 mm or less Voltage U0 ≈ (300-500) V counter gas Avalanche RI RA, several mean free paths needed Pulse height mainly due to positive ions (q+) W. Udo Schröder, 2012

  22. Solid-State Gamma Detectors W. Udo Schröder, 2012

More Related