Scientists are on the verge of discovering dark matter by using a very powerful detector filled with liquid xenon located a mile beneath Italy's Gran Sasso mountains. While searching for the dark matter particle, they were able to examine a rare event. The dark matter detector observed the decay of radioactive xenon-124.


Xenon-124 detector located underwater beneath Italy's Gran Sasso mountains. (Image Credit: Nature)

Their findings, published in Nature on April 24, is a collaboration by the XENON team made of over 160 scientists hoping to find dark matter by using the XENON1T detector. They have found that xenon-124, an isotope of the element xenon used in flash lamps and ion thrusters in spacecraft isn't as stable as they once thought. The detector contains a cylindrical tank containing just over 7,000 pounds of liquid xenon cooled down to a temperature of -139 degrees Fahrenheit. The detector is buried deep enough in the waters that it's shielded from radioactive interference that could be a threat to dark matter measurements.


The usability of fine-tuning and clean measurements from the XENON1T detector allowed scientists to observe the decaying of xenon-124 at a rate much longer than the universe's age by over a trillion times longer. In order to achieve this, the scientists measured the half-life of the atoms.


Xenon-124's half-life is measured at 1.8  x 10^22 years, which makes the entire detection extremely rare. There is also a massive amount of xenon atoms due to all the liquid xenon in the detector, which allows scientists to observe trillions of atoms. Even though a very small amount of that is xenon-124, it still gives a good chance of discovering such a rare event in the universe. Instead of observing the atoms decaying, the scientists just look for a the sign of decay, by keeping an eye out for x-rays and electrons that become released when xenon-124 decays.


The detector was only able to locate 126 processes in the span of two years, allowing scientists to calculate xenon-124's half-life. Even though the decay isn't relevant to finding dark matter, it still raises confidence in using the detector to find dark matter one day.


XENON1T was originally put on hold in December 2018 for an upgrade called XENONnT. This upgrade will contain a detector that's three times larger in size, giving it more room for liquid xenon, allowing it to be more sensitive to rare events that may lead up to the discovery of dark matter particles.


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