From Popular Mechanics
Scientists have a new precise measurement they say could help them finally make a nuclear clock, rather than a simply atomic one.
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Physicists from Gutenberg Universitaet Mainz (JGU) and other German scientists used an extremely tiny instrument—a magnetic microcalorimeter named maXs30—to measure movement within the nucleus of the isotope thorium-229. The scientists super-cooled the detector to minus 273 degrees Celsius to measure the “miniscule temperature rise that occurs when a gamma-ray is absorbed,” according to the JGU press release.
Thorium-229 is special among isotopes because of the extremely low energy of its lowest excited state, meaning it’s the best candidate for a measurable standard that can be used to make a practical clock. This isn’t something you’ll put on your nightstand, or even something that will likely be used inside your local university’s advanced computers. Its extreme specificity is most suited to measuring tiny blips in faraway space, for example, or in nano-fine experiments trying to detect gravity waves, or eventually something like dark energy.
But how do you tune a nuclear clock? Scientists need a specific wavelength of energy to use in order to build such a clock using the exact right laser, for example, and this has required countless experiments about the way thorium-229 behaves.
In this experiment, scientists paired a specially prepared uranium-233 with the thorium-229 in order to use their difference to measure time. The uranium isotope was isolated completely. “First, they chemically removed all decay daughter products that had built up over time before the sample was used. They also removed unwanted radioisotopes, the decay of which leads to an unwanted background in the measured data,” JGU explains.
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Up to this point, the experiment isn’t new. Scientists have had a fairly agreed-upon roadmap to a nuclear clock for decades and have chipped away at it piece by piece as a group. But this time, the German researchers used their magnetic microcalorimeter to measure the radiation more precisely, and their efforts bore fruit.
“They measured the transition energy at 8.1 electronvolts, which would mean an ultraviolet laser with a wavelength of 153.1 nanometers could be used to build the elusive nuclear clock,” according to another release.
“Some pairs of these nuclear clocks can detect energy changes of one part in 1014, being about 1,000 times more sensitive than the best atomic clock,” Britannica explains, where atomic clocks “are now predicted to be off by less than one second in more than 50 million years.”
Like the princess and the pea, a nuclear clock will detect an extremely small measurement from an almost unfathomable distance.
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