Introduction 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. 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. Theory By Faraday’s Law, a precessing nuclear magnetization of constant magnitude will induce a voltage in the sample coil proportional to Acknowledgments We wish to thank Pascal Mickelson of Rice University for allowing us to use his software within our programs. Methods Resonant nucleus: 1 H Sample: Mn(SO 4 ) + H2O 44.7x10 -3 M Magnetic field B 0 : T Radio frequency: MHz Averages: 10 Error bars: Standard deviation of mean Pulse programmer SpinCore PB24-50-PCI board LabVIEW 8.2 software Data acquisition National Instruments PCI-5102 digitizer LabVIEW 8.2 software Conclusions Title Names Department of Physics and Astronomy, Minnesota State University Moorhead, Moorhead, MN References 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. Results θ Spin up state Spin down state Magnetic field Sample coil Selects pulse channels and duration Digitizes NMR signal and averages data Increments pulse widths and averages for each width Data (red circles) were fit to the function V( τ) = A*exp(- τ /T)*sin(ω 1 τ +D) The results of the fit (black line) were: Chi 2 /DoF = 6.9x10 -6 R 2 = 0.95 A = (0.026 ± 0.001) V T = (210 ± 20) μs ω 1 = ( ± ) rad/μs D = (2.63 ± 0.05) rad From ω 1 the amplitude of the RF field B 1 may be calculated. The result was B 1 = (351± 2) μT 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. It may be shown [1] that ω 1 =γB 1 where γ/2π =42.58 MHz/T. 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. The signal amplitude oscillated as the pulse duration was increased, which is consistent with the prediction of Faraday’s Law. Analysis yielded B 1 = (351± 2) μT. The order of magnitude is consistent with values from other systems. The exponential decay of the signal amplitude may be due to the dispersion of the nuclear spins resulting from the magnetic field inhomogeneity. [1] C. P. Slichter, Principles of Magnetic Resonance, 3 nd Edition, Springer in Solid-State Sciences 1, 1990 Springer-Verlag.