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The Simple Concept Of NMR

The Simple Concept Of NMR. Sarah Newton University of Oregon Applied Physics. Background. Many applications in Chemistry and Medicine 1940's- First Signs of NMR

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The Simple Concept Of NMR

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  1. The Simple Concept Of NMR Sarah Newton University of Oregon Applied Physics

  2. Background • Many applications in Chemistry and Medicine • 1940's- First Signs of NMR • Bloch, Purcell, and others noticed the H nuclei had magnetic properties. It could absorb RF energy when placed in a field of a strength specific to the identity of the nuclei. • When absorption occurs, the nucleus is described as being in resonance.

  3. Objectives • Simulate different circuits to give the best resonance • Develop a detector Built within constraints: Resonance no higher than 13MHz. • See CW • See Pulsed • Compare and analyze their similarities and differences

  4. Connection to Optics • NMR and Optical Pumping have the same basic concept • Optical Pumping It is a two level system that electronically excites the constituents of a medium into another energy state. i.e. Laser

  5. What is NMR? • Type of Spectroscopy that manipulated the magnetic properties of nuclei within a sample • That manipulation leads to finding the chemical properties and environment contained within the sample.

  6. CW/Pulsed NMR • CW(Continuous Wave) NMR • Experiments have a varying frequency of radiation at constant magnetic field and measuring the absorption of radiation by the different nuclei. • Pulsed(Fourier Transform) NMR • Resonances are not measured one after another but all nuclei are excited at the same time by a radio frequency pulse. • Excited spins emit the absorbed radiation after the pulse. Intensities of several frequencies are calculated and framed into spectrum.

  7. Circuit Sim

  8. Sims Graph

  9. Circuit

  10. Methodology • Magnet is powered up • Sample lowered into quartz vial (connected to the circuit.) • RF gain(from radio receiver) increased to max • Capacitor dials on bridge circuit turned to minimize RF gain • Amps of DC power supply adjusted until a signal becomes visible on the oscilloscope. • The small function generator provides a“wobble” on the coils while the older generator is the driving unit

  11. Intrumentation

  12. Results (What Should have happened) • In the CW -fixed frequency and varying current -Able to observe the resonant signal (“wiggle”) at individual frequencies in succession • In pulsed -A short pulse containing a range of frequencies -All nuclei spins are excited( with a range of frequencies) -Induces a current creating an electrical signal response

  13. Conclusion/Summary • Success!!! Circuit works and is fully functional But.. Due to the strange disappearance and reappearance of resonance at different frequencies we will go back to the drawing board.

  14. Future Work • Simulations • Build a better circuit • Run both CW and Pulse NMR

  15. Acknowledgements • Material Science Institute • Stephen Gregory and Brian Boggs

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