Sarah Newton University of Oregon Applied Physics.
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Transcript of Sarah Newton University of Oregon Applied Physics.
Sarah NewtonSarah Newton
University of OregonUniversity of Oregon
Applied PhysicsApplied 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 PumpingIt 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