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The First Nuclear Clock Will Test if Fundamental Constants Change (www.quantamagazine.org)

submitted 2 months ago by [email protected] to c/[email protected]

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An ultra-precise measurement of a transition in the hearts of thorium atoms gives physicists a tool to probe the forces that bind the universe.

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[–] mark3748 11 points 2 months ago

The Idaho researchers observed that reversing the intrinsic angular momentum, or “spin,” of thorium-229’s outermost neutron seemed to take 10,000 times less energy than a typical nuclear excitation. The neutron’s altered spin slightly changes both the electromagnetic and strong forces, but those changes happen to cancel each other out almost exactly. Consequently, the excited nuclear state barely differs from the ground state. Lots of nuclei have similar spin transitions, but only in thorium-229 is this cancellation so nearly perfect.

Basically, thorium-229 can be excited by conventional lasers instead of gamma rays. Instead of millions of electron volts, it takes less than 10, which means it’s more reliable and more precise.