Xenon-124 is one such elder statesman: Its half-life is one trillion times longer than the age of the universe, and as such, the chance of detecting its decay is very small. Some elements, however, decay very, very slowly. Radon-222, for example, has a half-life of just four days. We’re much more familiar with radioactive elements like uranium and plutonium-these are the wild teenagers of radioactive elements, constantly hurling off particles.
Depending on their makeup, some will stabilize themselves by releasing subatomic particles and turning into an atom of a different element-a process called radioactive decay. The results from the XENON1T experiment, co-authored by University of Chicago scientists and published April 25 in the journal Nature, document the longest half-life in the universe-and may be able to help scientists hunt for another mysterious process that is one of particle physics’ great mysteries. Along the way, however, the detector caught another scientific unicorn: the decay of atoms of xenon-124-the rarest process ever observed in the universe. Deep under an Italian mountainside, a giant detector filled with tons of liquid xenon has been looking for dark matter-particles of a mysterious substance whose effects we can see in the universe, but which no one has ever directly observed.
