Resonating with the Next Generation · 4:31pm Mar 4th, 2021
Izzy Moonbow explains the principle of spin precession and Nuclear Magnetic Resonance to Sunny Starscout with the aid of a tennis ball.
“It’s called Nuclear Magnetic Resonance!”
Izzy spoke the technical phrase in a loud clear voice with a gleeful smile while bouncing a tennis ball against the ground with a forehoof. The motion shook her blue mane and a few locks fell down in front of her eyes. This distraction caused her to miss the ball, which bounced away. Sunny leapt up and kicked it back. It sailed across the room and impaled itself on the point at the tip of the unicorn’s horn. Izzy crossed her eyes trying to see the result.
“This is perfect.” She laughed. “Think of the ball as a proton—the nucleus of a hydrogen atom. Protons have a spin.”
She brushed a hoof against the ball to spin it around her horn.
“They can be Spin Up—”
She pointed her horn, with the ball, straight up the air while looking down her nose at her friend.
“—or Spin Down.”
She jumped up, twisting her body around in mid-air. When her four hooves hit the ground, her head and horn were pointing down. She flicked her tail to the side and grinned at Sunny between her legs.
“The proton itself is a little magnet. When it’s in a magnetic field, it can align itself with the spin in the direction of the field—or in the opposite direction.”
Izzy jumped and down a few times to illustrate the Spin Up and Spin Down states. “Or—if we rotate the spin—”
She balanced on tip of one hoof, adjusting her centre of gravity so her horn was now at an angle halfway between vertical and horizontal. Then, with a kick of a hind hoof, she pirouetted around. Her mane and tail flowed around her in a blue swirl as she rotated, while the ball on her horn traced out a cone. Sunny noted, with admiration, that her new friend was clearly a talented ballerina, as well as a physicist and tennis player.
“—it precesses about the magnetic field. Like a spinning top. And it does so at its own resonant frequency.”
After a few more twirls she sat down and looked at Sunny.
“As they are all little magnets, when they precess around, protons will generate an electromagnetic wave at their resonant frequency. The frequency will vary with the magnetic field, and may be shifted up or down a bit by the other particles around it. Other nuclei will have their own resonant frequencies. Isn’t this amazing?”
“That’s cool,” agreed Sunny. “How can we make them all dance like that?”
“First line them up in a magnetic field. Then you need to apply a magnetic pulse oscillating at a frequency close to their resonance. That will set them off precessing.”
“You wave at them the way they like and they wave back,” said Sunny.
“Yes,” said Izzy. “Then if we could sense the magnetic field, we could hear them. We could tune into this electromagnetic signal, and measure the resonant frequency, and do all sorts of things. We could scan objects to see what nuclei are inside—and see what materials they are made of. Or we could measure the strength of the magnetic field, or build a body scanner…”
“Could you build that?” asked Sunny.
Izzy stopped smiling. “That’s the trouble. It’s not that easy to detect the signal.”
“Pick up an electromagnetic signal? Like with a radio set?” said Sunny.
“Yes,” said Izzy. “But to reach radio frequencies, you would need a very big magnetic field. It would take a lot more than those little Twilight Sparkle and Rainbow Dash magnets you have stuck on your fridge door.”
“Use superconductors,” said Sunny.
“What?”
“Take some niobium wire. Cool it down super-cold. It’s a superconductor. Zero resistance. You set up an electric current flowing round a loop and it will keep going forever and that will make your very big magnetic field.”
Sunny walked over and tidied her friend’s mane, which had been thrown out of place by all her pirouettes, then rubbed her head against Izzy’s neck.
“You’re not the only pony who knows some physics.”
“You can build that?”
“Sure. With a bit of help.”
Izzy’s face lit up. She threw her forelegs around Sunny and hugged her.
“This is so cool! We are going to have such awesome epic adventures together.”
We don't even know who they are as people, and you're already having them teach us about physics.
Never change, Pineta.
Science! I expect they will wrangle Pipp into gathering the helium they need.
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It's here that I'm forced to remind you about what Faust said on the topic of pegasus flatulence. I believe the phrase "literal ****storms" appeared, and for the record I am so sorry.
Most adorable lecture on subatomic physics, ever!
I thought GMR heads in hard drives were as much as a quarter the sensitivity of SQUIDS, and could operate at magnetic fields that were percentage that of liquid helium cooled niobium, as liquid nitrogen 123 can only work to about 4 or 5 Tesla before the field kills them?
Noone can make a concentrated pulse magnetic field that lasts long enough for the precession effect to occur, or you wouldnt need the big coil at all, but a tricorder?
I have the biggest dumb smile on my face right now. You are wonderful.
I'll be disappointed if this isn't canonically plausible now. (Just kidding, but it would be fun if it were!)
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Physics is for everypony. And now is the time to get your Sunny and Izzy story out before any more information forces you to adapt your interpretation of their characters and things get complicated.
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That raises a few questions... and could lead to interesting results.
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Maybe this is just the start. Maybe Izzy and Sunny could do a whole lecture series.
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We can usually find a way to make things canonically possible. With a bit of imagination.
I bet my grades in HS would have been so much better if I had them for teachers or student-aides.
Love it!