2023 BFY4 Abstract Detail Page
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| Abstract Title: |
Visualizing NMR: Some Lessons with VPython |
| Abstract: |
The Bloch equations, and their extension by Hahn to treat an ensemble, form the foundation of the phenomenology of nuclear magnetic resonance. The understanding of NMR measurements in terms of these equations presents the student with a challenge in geometric imagination: to see in the mind's eye the "spins" (magnetic moments with angular momentum) evolve under the influence of static and dynamic fields (including pulsed fields), and relaxation. By making use of computational tools such as VPython, one can aid the imagination with animated simulations. I show a few selected lessons using interactive VPython programs that illustrate the spin dynamics predicted by the Bloch equations and how they predict measurements made by the TeachSpin PS1 NMR spectrometer. Some examples: Switching between the lab and rotating reference frame; Continuous excitation with a weak RF field; Off-resonance versus on-resonance; Spin echos and Hahn's pi/2 - pi/2 "eight-ball;" The Carr-Purcell sequence and the Meiboom-Gill correction for pulse-width error; Off-resonance spin echos; Measuring T1 with the inversion-pulse sequence versus a rapid pi/2 sequence. In addition, the simulations reveal an interesting and beautiful geometry to evolution of spin ensembles, with the appearance of organized states ("internal echos") that do not produce a signal due to their symmetry. |
| Abstract Type: |
Poster
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Author/Organizer Information |
| Primary Contact: |
David B. Pengra
University of Washington
Seattle, WA 98195-1560
Fax: 206-685-0635
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Co-Author(s)
and Co-Presenter(s) |
None
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