Posted on April 24, 2019
"We actually saw this decline. This is the longest, slowest process ever directly observed, and our dark matter detector was sensitive enough to measure, said Ethan Brown, assistant professor of physics at Rensselaer Polytechnic Institute. "It's amazing to have witnessed this process, and he says our detector can measure the rarest thing ever recorded."
How do you observe a process that takes more than a trillion times longer than the age of the universe? The research team at XENON Collaboration has done it with an instrument that can find the heaviest particle in the universe – dark matter. In a paper to be published tomorrow in the journal Nature, researchers announce that they have observed the radioactive decay of xenon-124, which has a half-life of 1.8 x 1022 years. The XENON collaboration introduces XENON1T, a 1,300-kilogram vat of high-purity, liquid xenon protected from cosmic rays in a cryostat located in 1,500-meter-deep waters beneath the Italian Gran Sasso Mountains. Researchers are looking for dark matter by recording tiny flashes of light that occur when particles inside the detector interact with xenon. And while XENON1T was built to capture the interaction between a dark matter particle and the nucleus of a xenon atom, the detector actually picks up signals of any interaction with the xenon.
Dark Matter – "From an Eon before the Big Bang" (Weekend Feature)
The evidence for xenon decay was produced as a proton in the nucleus of a xenon atom converted into a neutron. For most elements that are subject to decay, this happens when an electron is pulled into the nucleus. However, a proton in a xenon atom must absorb two electrons to be converted into a neutron, an event called "double electron capture."
Dual electron capture only happens when there are two electrons next to the nucleus At the right time, Brown said, which is "a rare thing, multiplied by another rare thing, which makes it extremely rare."
When the ultra-rare cases occurred and a double-electron trap occurred within the detector, the instruments seized the signals from electrons in the atom, which were rearranged to fill in the two that were absorbed in the nucleus.
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"Electrons that are caught twice are removed from the innermost shell around the core, and this creates space in this shell," Brown said. "The remaining electrons collapse into the ground state, and we have seen this breakdown in our detector."
For the first time, scientists have measured the half-life of this xenon isotope based on direct observation of its radioactive decay
"This is a fascinating insight that expands the boundaries of knowledge of the most fundamental properties of matter, "said Curt Breneman, dean of the School of Science. "DR. Brown's work calibrating the detector and ensuring that the highest purity grade of xenon was cleaned was critical to this important observation."
Very strange galaxies – "The absence of dark matter is unprecedented" ]
The XENON Collaboration comprises more than 160 scientists from Europe, the United States and the Middle East and has since 2002 deployed three successively more sensitive liquid xenon detectors in the Gran Sasso National Laboratory in Italy. The XENON1T, the largest detector of its kind ever built, collected data from 2016 to December 2018 when it was turned off. Scientists are currently updating the experiment for the new XENONnT phase, which will have a three times larger active detector mass than XENON1T. Together with a reduced background, the sensitivity of the detector is increased by an order of magnitude.
Three years ago, researchers were excited that a galaxy in the heart of the Abell 3827 cluster at the top of the appearing page was separated from the dark matter that surrounded it. New research suggests that this is wrong. (NASA / ESA / Richard Massey)
The Daily Galaxy via the Rensselaer Polytechnic Institute