ELECTRON SPIN RESONANCE Dylan Prendergast Advanced Lab, Fall

ELECTRON SPIN RESONANCE Dylan Prendergast Advanced Lab, Fall

ELECTRON SPIN RESONANCE
Dylan Prendergast
Advanced Lab, Fall 2007

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
8.871 GHz + .005 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
fields power supply, electron spin
resonance was observed with a
magnetic field of 3.14 KG with an
error of + .03. This error is a result
of the fluctuating magnetic field
produced by the secondary magnet.

HEADERS ALL CAPS 30 POINT
BOLD
Body of type, cap, and lower case, 28
point bold.

-Calculate g
-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.

After converting to appropriate
units, the measured value of
g was 2.0184. 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.

-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 = (h)/BH
Where: h = Planks constant
v = Klystron frequency
B = Bohr magneton
H = Main magnetic field

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.

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