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Title
Names
Department of Physics and Astronomy, Minnesota State University Moorhead, Moorhead, MN 56563
Abstract
We designed a computer controlled pulse
programmer for a student-built nuclear
magnetic resonance (NMR) spectrometer
using a National Instruments digitizer card,
LabVIEW 8.2 software, and a SpinCore
PulseBlaster card.
Initial results were
encouraging.
Theory
Results
By Faraday’s Law, a precessing nuclear
magnetization of constant magnitude will
induce a voltage in the sample coil
proportional to
The pulse programmer performed in under
five minutes an experiment that had taken
over an hour to perform manually. The data
are shown and analyzed below.
θ
Magnetic
field
Sample coil

Spin down state
Methods
For a sample, the number of spins is
comparable to Avogadro’s number, and the
total nuclear magnetization behaves as a
classical magnetization. The angle between
the external magnetic field and the nuclear
magnetization can be changed with a RF
pulse, and controlled by the duration (τ) of
the RF pulse.
It may be shown [1] that
ω1=γB1
where γ/2π=42.58 MHz/T.
Resonant nucleus:
Sample:
Magnetic field B0:
Radio frequency:
Averages:
Error bars:
1H
Mn(SO4) + H2O
44.7x10-3 M
0.9883 T
42.248490 MHz
10
Standard deviation of
mean
Pulse programmer
•SpinCore PB24-50-PCI board
•LabVIEW 8.2 software
Signal amplitude (V)
0.02
The nucleus of a hydrogen atom has
magnetic dipole moment and spin angular
momentum. When placed in an external
magnetic field, two distinct states form,
separated in energy. The nuclear spin axis
“precesses” around the magnetic field
Radio frequency (RF) waves with the same
frequency as the precession frequency of
the nuclear spins can cause the nucleus to
flip from the spin up to the spin down state.
The pulse programmer functioned mostly as
anticipated. However, some minor problems
arose during data acquisition, and will need to
be corrected before the system can be used
for longer measurements. These problems
included: the occasional halting of program
execution; RF pulses staying on after end of
automatic acquisition.
  sin 
Introduction
Spin up state
Conclusions
The signal amplitude oscillated as the pulse
duration was increased, which is consistent
with the prediction of Faraday’s Law.
0.01
0.00
Analysis yielded B1 = (351± 2) μT. The order of
magnitude is consistent with values from
other systems.
-0.01
The exponential decay of the signal amplitude
may be due to the dispersion of the nuclear
spins resulting from the magnetic field
inhomogeneity.
-0.02
-0.03
0
50
100
150
200
250
 (s)
Data (red circles) were fit to the function
V(τ) = A*exp(-τ/T)*sin(ω1τ+D)
The results of the fit (black line) were:
Chi2/DoF
= 6.9x10-6
R2
= 0.95
Data acquisition
•National Instruments PCI-5102 digitizer
Digitizes NMR signal
•LabVIEW 8.2 software
and averages data
Selects pulse
channels and
duration
Increments pulse
widths and averages
for each width
300
A = (0.026 ± 0.001) V
T = (210 ± 20) μs
ω1 = (0.0938 ± 0.0004) rad/μs
D = (2.63 ± 0.05) rad
From ω1 the amplitude of the RF field B1 may
be calculated. The result was
B1 = (351± 2) μT
References
[1] C. P. Slichter, Principles of Magnetic
Resonance, 3nd Edition, Springer
in Solid-State Sciences 1, 1990
Springer-Verlag.
Acknowledgments
We wish to thank Pascal Mickelson of Rice
University for allowing us to use his
software within our programs.