Thorium Nuclear Clocks

[John Clark]

Existing atomic clocks are stable to within 1 part in 10^20, if two of them had been synchronized 13.8 billion years ago during the Big Bang today they would disagree with each other by less than 1/100 of a second. But scientists want something better, they want to make a nuclear clock, which works by measuring the oscillation of the protons in an atom's nucleus, not an atomic clock, which works by measuring the oscillation of an atom's electrons. The basic reason for this improvement in precision is that an atom is about 10^-10 meters across but a nucleus is only about 10^-15 meters across, that's a very small antenna and so is far less susceptible to picking up environmental interference,  so a nuclear clock would be at least 10 times more accurate than an atomic clock

To make a nuclear clock you need a Laser to stimulate a nucleus to a precise level but, although there are about 3000 different nuclei you could use, with only one exception they all have transition levels in the Gamma or hard X-ray region and it's impractical to make a laser with a frequency that high. It's been known for a long time that the energy transition level for an isomer of Thorium-229 is remarkably low, only about 8 electron volts, that's in the ultraviolet range and making a laser in that range is entirely feasible if you know the exact frequency, unfortunately "about 8 electron volts" is not nearly precise enough. But thanks to a new measuring technique and a new paper in Nature,  it's now known to be 8.338 electron volts and the half-life of the Thorium 229  isomer is found to be 670 seconds. That's still not precise enough to engineer a laser that can excite Thorium-229, but with this new measuring technique researchers are pretty confidence it's only a matter of time before they have an even more precise number.

With a GPS system based on a Thorium nuclear clock you could easily know your position to a fraction of an inch versus several feet with the current GPS, it would be so good the navy could use it to land jets on aircraft carriers automatically even in heavy seas. And it could also enable you to measure very very small changes in the gravitational field because the stronger the gravity the slower the clock, and that would let you make detailed underground maps. A nuclear clock would be so accurate you could even test to see if some of the fundamental constants of nature are really constant or are changing with time. 

Observation of the radiative decay of the Thorium-229 isomer and its use in nuclear clocks

John K Clark    See what's on my new list at  Extropolis

tnc

[spudb...@aol.com]

Sorry, I obsess. If I'd have my druthers, I'd druther have the lads at RIKEN in Japan create a fail-safe Thorium 232/U233 reactor to power civilization for the next 10 millennia, then a nice, atomic clock. Moreover, some years ago, the Canadians left their original Candu reactor (Th232-->U233) in a heavy water reactor (deuterium) and went Yankee light water. Cheaper, I expect. But, you knew that already

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