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Structure of Electron Paramagnetic Resonance spectrometer

2014.02.04 RPLab Tuesday Seminar. Structure of Electron Paramagnetic Resonance spectrometer. Kwon Choi. Electron Paramagnetic Resonance (EPR). A spectroscopy technique based on the absorption of electromagnetic radiation by a paramagnetic sample . Paramagnetic?

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Structure of Electron Paramagnetic Resonance spectrometer

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  1. 2014.02.04 RPLab Tuesday Seminar Structure of Electron Paramagnetic Resonance spectrometer Kwon Choi

  2. Electron Paramagnetic Resonance (EPR) A spectroscopy technique based on the absorption of electromagnetic radiation by a paramagnetic sample. • Paramagnetic? • Paramagnetic properties due to the presence of some unpaired electrons http://encyclopedia2.thefreedictionary.com/Electron+Paramagnetic+Resonance+EPR

  3. Thermo Luminescence EPR

  4. Origin of an EPR signal Anti-Parallel, E = Microwave E = geBB0 = : g-factor (Zeeman splitting) for unpaired electrons : Bohr magneton = 9.27x10-24 J/T Parallel, E = -

  5. How energy absorption occur 1. Under the resonance : E = Energy emission Energy absorption Both transitions with same probability E = - 2. Population distribution of electrons between two energy levels : (Boltzmann’s equation) = T : temperature k : Boltzmann constant The population of the lower level is greater than that of the upper level. Net energy absorption http://encyclopedia2.thefreedictionary.com/Electron+Paramagnetic+Resonance+EPR

  6. Absorption spectrum EPR spectrum E = = geBB0 Sweep in order of only a few gauss http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Magnetic_Resonance_Spectroscopies/Electron_Paramagnetic_Resonance/EPR%3A_Interpretation

  7. Difference in measurement method from NMR Too short for time-domain! http://afni.nimh.nih.gov/sscc/staff/rwcox/ISMRM_2006/ISMRM%20M-F%202006/files/FA_07.pdf

  8. D:\Dropbox\RadiationPhysics\Textbook\Electron Paramagnetic Resonance - A Practitioner's Toolkit\03. ch2.pdf

  9. Components of EPR spectrometer Spectrometer detection method Measure the amount of radiation that is reflected back out of the resonator. In resonator, Circulator Waveguide Oscillator Detector Lock-In Amplifier Oscillator Power Power Supply Multimeter Gaussmeter Thediode detector is mounted along the microwave and produced a current proportional to the microwave power reflected from the cavity.

  10. Components of EPR spectrometer Circulator Waveguide Oscillator Detector Lock-In Amplifier Oscillator Power Power Supply Multimeter Gaussmeter Oscillator Microwave source Generally a klystron tube or a gunn diode

  11. Components of EPR spectrometer Circulator Waveguide Oscillator Detector Lock-In Amplifier Oscillator Power Power Supply Multimeter longer Gaussmeter Oscillator Microwave source Penetration depth Generally a klystron tube or a gunn diode Several kind of microwave frequency bands shorter

  12. Components of EPR spectrometer Circulator Waveguide Oscillator Detector Lock-In Amplifier Resonator Oscillator Power Power Supply Multimeter Gaussmeter Resonator

  13. Why resonator is needed? General optical spectroscopy ; Detect how much light gets through. Very inefficient in EPR spectroscopy Need to enhance the sensitivity. So Microwave Resonator is used.

  14. Components of EPR spectrometer Circulator Waveguide Oscillator Detector Lock-In Amplifier Resonator Oscillator Power Power Supply Multimeter Gaussmeter Resonator Helps increase sensitivity by “focusing” or “concentrating” the microwave power at the sample. Various designs Correspond to a specific wavelength of microwave

  15. A Little More Details of Resonator Circulator Waveguide Oscillator Detector Lock-In Amplifier Resonator Oscillator Power Power Supply Multimeter Gaussmeter Iris A connection between the wave guide and the resonator cavity Couple the microwaves into the cavity via an iris. Iris screw in front of the iris that we can adjust the “matching”.

  16. Various shapes of resonators (here; a metal box) Store MW energy in the form of the standing wave Magnetic field drives the absorption. Specific to the wavelength of MW

  17. Circulator & Isolator Circulator Waveguide Oscillator Detector Lock-In Amplifier Oscillator Power Power Supply Multimeter Gaussmeter Circulator Transmit microwave only to a fixed direction - Oscillator -> Resonator - Resonator -> Detector Isolator A kind of circulator Transmit microwave only in one direction

  18. Circulator & Isolator Circulator Waveguide Oscillator Detector Lock-In Amplifier Oscillator Power Power Supply Multimeter Gaussmeter Circulator Transmit microwave only to a fixed direction - Oscillator -> Resonator - Resonator -> Detector Isolator Correspond to a specific wavelength of microwave RF Circulator RF Isolator Transmit microwave only in one direction Yixin Microwave Electronics Co., Ltd.

  19. Circulator Waveguide Oscillator Detector Lock-In Amplifier Oscillator Power Power Supply Multimeter Gaussmeter Lock-in Amplifier Detect and measure very small AC signals (~ few nV) Use phase-sensitive technique for noise filtering

  20. Experimental example Simple experimental setup to see EPR phenomena Helmholtz coils RF Oscillator - 10 MHz ~ 18 MHz (RF range) - 50 Hz current through Helmholtz coils Oscilloscope Signal processing using Lab view

  21. Response curve for dosimetry Peak-to-peak amplitude of the most intense EPR peak Dose resopnse peak-to-peak intensity vs. dose EPR spectrum in the first-derivative form

  22. Thank you for your attention.

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