1. ELECTRON SPIN RESONANCE Dylan Prendergast Advanced Lab, Fall 2007
ABSTRACT
METHODS
DISCUSSION
This experiment is designed to observe electron spin resonance in a sample of material. A standing electromagnetic wave is created using a klystron, and by placing the sample of material on an anode of the wave and in a magnetic field, electron spin resonance can be observed. By measuring the klystron frequency and the strength of the magnetic field, an experimental value of the electron paramagnetic resonance factor (g) can be found.
The Setup:
-Measure the Klystron Frequency
By adjusting the tunable short, the klystron frequency was measured as GHz GHz with the small error occurring as a result of the scale on the tunable short.
-Observe Electron Spin Resonance
Electron spin resonance in a sample of DPPH was sought. After several sweeps through the available range of current on the main magnetic field’s power supply, electron spin resonance was observed with a magnetic field of 3.14 KG with an error of This error is a result of the fluctuating magnetic field produced by the secondary magnet.
-Calculate g
After converting to appropriate units, the measured value of
g was This is very close to the accepted value of g, which is 2.
-Repeat with different samples
The process was repeated for a second sample, Manganese chloride, but electron spin resonance was not observed.
HEADERS ALL CAPS 30 POINT BOLD
Body of type, cap, and lower case, 28 point bold.
INTRODUCTION
-The klystron produces an electromagnetic wave within a wave guide with a fixed frequency which can be measured experimentally
-An oscilloscope is used to display the wave generated by the klystron, and to show destructive interference, as produced in a resonance cavity to find the klystron frequency, or constructive interference, as produced when electron spin resonance is observed.
-A magnetic field, with a strength governed by a variable power supply is created using electromagnets. The sample of material is placed in this magnetic field in order to observe electron spin resonance.
-To aid in the detection of electron spin resonance, a second, weaker magnetic field is created which oscillates over a very small range. The second magnetic field runs parallel or anti parallel to the main magnetic field, and is controlled by a function generator.
-Measure the Klystron Frequency
Power on the Klystron and connect the oscilloscope to the detector between the wavemeter and the tunable short. Adjust the oscilloscope until a standing wave appears. Adjust the tunable short until destructive interference can be observed on the oscilloscope. The frequency indicated on the tunable short is the frequence of the klystron.
-Observe Electron Spin Resonance
Connect the oscilloscope to detectors as shown by the arrows. Adjust the positions of the detectors located at each point until standing waves of equal magnitude are seen on the oscilloscope's two channels. Switch the oscilloscope to the “add” function.
Insert the sample of material into the magnetic field and turn on the signal generator for the secondary magnetic field. Sweep through the available current range in order to vary the main magnetic field. When the trace on the oscilloscope jumps, electron spin resonance has been reached. Record the value of the magnetic field.
-Calculate g
g = (hν)/μBH
Where: h = Plank’s constant
v = Klystron frequency
μB = Bohr magneton
H = Main magnetic field
CONCLUSION
The experiment allows for an accurate calculation of the electron paramagnetic resonance factor (g). The accepted value falls within the margin of error of the experimentally calculated value.