Nuclear
Magnetic Resonance Nuclear
Magnetic Resonance
In this experiment, students will examine the phenomenon of nuclear magnetic resonance (NMR). This is a quantum mechanical effect, by which the energy levels of a nucleus are split due to the interaction between the nuclear magnetic moment and an external B-field. These moments can be aligned parallel or anti-parallel to the applied field, resulting in an energy difference of twice the product of the field strength and the z-component of the magnetic moment. Transitions between the two energy states are associated with absorption or emission of radio frequency (rf) photons.
A small coil will be submerged in the samples being studied. The coil forms the inductance of an LC resonant oscillator, the frequency of which can be tuned by adjusting the capacitance. A uniform external B field is obtained using either a 4.7 kG permanent magnet, or an electromagnet capable of producing fields up to 1 T. Both magnets are rigged with helmholtz coils driven at 60 Hz which superimposes a small time-varying component to the magnetic field; the sample is thus "swept" through resonance at a frequency of 60 Hz. The NMR is observed as loading on the coil due to absorption of rf photons; this is monitored using an oscilloscope. The frequency of the rf signal is monitored using either a shortwave radio or a frequency counter.
Page prepared by Grant Coble and Barb Mattson (Fall '97), modified by K.M.