Commanding the Power of Thor…ium: “Wigner Crystals of 229Th for Optical Excitation of the Nuclear Isomer”

ResearchBlogging.orgI have to admit, I’m writing this one up partly because it lets me use the title reference. It’s a cool little paper, though, demonstrating the lengths that physicists will go to in pursuit of precision measurements.

I’m just going to pretend I didn’t see that dorky post title, and ask what this is about. Well, it’s about the trapping and laser cooling of thorium ions. They managed to load thorium ions into an ion trap, and use lasers to lower their temperature into the millikelvin range. At such low temperatures, the ions in the trap “crystallize.”

So, they’ve demonstrated that if you get something cold, it forms a solid? Dude, that’s not shocking new physics. There are scare quotes around “crystallize” for a reason. They’re not forming a real crystal, in large part because we’re talking about triply ionized thorium here, so each has a charge of +3 electron charges. They repel each other pretty strongly, and if they weren’t held in a trap, they’d fly apart at high speed rather than forming a solid.

The “Wigner crystal” that forms is a regularly spaced arrangements of these ions, each being more or less stationary, separated from all its neighbors because of the electric force between them.They make these really nifty pictures using light scattered by the ions during the cooling process, so that each ion shows up as a dot of light:

i-c0ea832616e1fc64406037cf8fe670e8-thorium_ions.jpg

Pretty blue dots! That’s false color– the actual light being used is in the infrared, at 984 nm. But yes, it’s a pleasing color choice.

Continue reading “Commanding the Power of Thor…ium: “Wigner Crystals of 229Th for Optical Excitation of the Nuclear Isomer””