Nuclear Magnetic Resonance
This is the permanent magnet (background) and all the equiment
needed for the nuclear magnetic resonance lab except for the...
electromagnet.
Nuclear magnetic resonance (nmr) measurements
began as ways to determine nuclear magnetic moments. With this experiment,
the student will observe nmr for protons in a magnetic field and then use
this information to study the relationship of magnetic field and current
in an electromagnet. Finally the student will observe nmr in an unknown
nucleus. Three problems must be considered and dealt with in performing
this experiment: 1) the probability for absorption and stimulated emission
are equal if both energy states are equally populated, so there is no net
absorption; however at room temperature there is a slight favoring of lower
energy population, so very sensitive equipment will see the effect;
2) there is a tendency for the population states to equalize if resonance
is held too long, so generally resonance is swept through at a certain
frequency (60 Hz in this case using Helmholtz coils); 3) the magnetic
field must be constant through the sample. In this experiment, the
student will find the nmr of a glycerol probe using both a permanent magnet
and an electromagnet. To do this, the student inserts the probe into
the magnet and adjusts the frequency of the LC circuit set up by a coil
in the probe. As the frequency is adjusted, the student will see
the resonance condition on an oscilloscope. Once this has been accomplished
in the electromagnet, the student will also explore the relationship between
current through the magnet and the magnetic field, using the accepted value
for the proton's magnetic moment. Finally, the student will repeat
this process using an unknown, and using the information from the first
part of the experiment, the student should be able to determine the magnetic
moment of the unknown and the unknown's identity from a table of
the magnetic moments of the nuclei.
