Sarah Newton University of Oregon Applied Physics

  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. Background

  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 Objectives

  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 Connection to Optics

  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. What is 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. CW/Pulsed NMR

 Circuit Sim

 Sims Graph

 Circuit

  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 Methodology

 Intrumentation

 (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 Results

  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. Conclusion/Summary

  Simulations  Build a better circuit  Run both CW and Pulse NMR Future Work

  Material Science Institute  Stephen Gregory and Brian Boggs Acknowledgements