video 5: fixing up a non-homogeneous field via shimming coils: I wondered how the shimming coils could be effective if they were not installed in the apparatus; your demonstration could be more clear if you add an on-screen text pop-up stating that an identical shimming coil pack is already installed in the Terranova apparatus, and is operational in the final test. This is a terrific series of videos; thank you for the specific and accessible physics insights!
Really excellent presentation. Sadly, the presenter died in 2012 (look him up on Wikipedia - he was one of the most famous NZ scientists ever). No disrespect to him, but I must admit that I find it distracting that he often clearly says "magetization" instead of "magnetization" :)
Why is the prepolarizing field generated in the same direction as the oscillating transverse field? Shouldn't they be orthogonal to each other? Or does the prepolarizing field just ensure a large amount of similarly oriented protons, which all then shift to orient with the earth's field, which is fairly orthogonal to the oscillating transverse field? If that's the case, then once you get a bunch of protons oriented in the same direction, they tend to stay oriented with each other.
@5:19 A beautiful explanation easy to understand and remember. @ 6:10 (he left out) the stimulus field is very small compared to strength of the static field.
I thought you originally said that the signal that kicks the hydrogen momements off the rest state was at the precession frequency, but here you say it is about 1 ms. Does this mean that it is only 2 cycles of the 2+kHz signal? Why couldn't this simply be a DC field to hold the H-moments for a while at 90 degrees to the static (precession causing Earth) field, then let the moments decay back to the Earth field orientation? Regards, Steve N.
Paul, As an EE, I understand very well: resonance, presession, NMR in hydrogen and both the time and spectrum (fourier) domains as well as most of the other fundamentals, but have the same issue as Eric Stewart below: The difference between the pre-polarizing "pulse" and the earth's field illudes me. If Earth's field is producing the main precession causing field, what does the pre-polarizing field actually do? Does it shift the hydrogen moments away from the vertical to the horizontal so we can then watch the precession decay back to the Earth orentation? I thought that required an AC field that is resonant with the Hydrogen's precession freq. Is the pre-polarization field a DC field, or 2+ kHz field? On to #5... Regards, Steve N.
As an EE who understands Precession, Resonance and NMR basics, This one finally gets to the areas I have been having trouble learning, namely how the three dimensions are resolved. On to #4.
