Thanks to the XENON1T dark matter detector located beneath the Gran Sasso mountains in Italy, scientists have detected one of the rarest events ever discovered: a specific type of radioactive decay in xenon-124.
It's an amazing achievement because the decay of this isotope is extreme, extremely slow. In fact, xenon-124 has a half-life of 1.8 x 10 over the power of 22 years – about a trillion times longer than the age of the universe.
In radioactive decay, half-life refers to the time for half of the atomic nuclei in a given sample that would spontaneously change due to one of the many types of radioactive decay, often spitting out or trapping protons, neutrons and electrons in different combinations includes.
In this case, a research team succeeded in observing a special event called a double-electron trap, in which two protons within a xenon atom simultaneously absorbed two electrons, resulting in two neutrons ̵
This exciting observation was made thanks to the incredibly precise calibration of XENON1T – the instrument is designed to study interactions of hypothetical particles of dark matter with atoms in the 1,300 kilograms (2,866 lbs ) of xenon isotopes packed into the tank of the device.
In this case, the sensors designed to monitor such interactions detected the isotope decay itself, resulting in a rare observation
"We have actually seen how this disintegration occurred," sa One of the researchers, Ethan Brown of the Rensselaer Polytechnic Institute (RPI) in New York. "It's the longest, slowest process ever directly observed, and our dark matter detector was sensitive enough to measure it."
"It's amazing to have witnessed this process, and he says that our detector can ever measure the rarest things ever recorded."
Scientists have never directly observed the radioactive decay of this xenon isotope, even though its half-life since 1955 has been theorized. This is a direct proof of something we have been looking for for decades.  What actually happens is that XENON1T detects the signals emitted by electrons in the atom, rearranging themselves to pick up the two signals contained in the core. As Gizmodo reports, it does not quite meet the statistical threshold to be considered a discovery, but it is still an incredible observation.
"Electrons that are caught twice are removed from the innermost shell around the core, and this creates space in this shell," says Brown. "The remaining electrons collapse into the ground state, and we saw this breakdown in our detector."
Although XENON1T was built for the search for dark matter, it shows how these instruments can lead to other important insights. This latest observation could teach us more about neutrinos, abundant but difficult to detect particles that scientists have hunted for decades.
In this case, the researchers saw a two-neutrino double-electron trap – the result of the rearrangement of electrons Two neutrinos were emitted from the atomic nucleus. The next challenge they will face is the detection of a neutron-free double electron trap – an event even rarer than this.
This, in turn, could help unravel some of the deepest secrets of particle physics.
"This is a fascinating result that extends the boundaries of knowledge of the most basic properties of matter," says Curt Breneman of the RPI, who was not directly involved in the study.
"Dr. Brown's work on calibrating the detector and making sure that the xenon is cleaned to the highest possible degree of purity, was crucial to this important observation."
The research was conducted in Nature released.