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