As groundbreaking as the new discovery is, that wasn't the primary goal of the XENON1T experiment. It's designed to hunt for evidence of dark matter, these experiments can help capture the rare times dark matter interacts with normal matter.
The XENON1T experiment has now revealed the longest half-life ever seen in an element, which is far, far longer than the age of the universe.
Xenon 124 was already thought to have a long half-life – about 160 trillion years, but the new observation makes that look like the blink of an eye.
According to this study, the half-life of xenon 124 is a barely-comprehensible 18 sextillion years, or an 18 followed by 21 zeroes. For comparison's sake, that's more than a trillion times longer than the age of the universe itself, which is a mere 14 billion years young. That also means xenon 124 has the longest half-life ever measured in a material, stealing the crown from bismuth 209 and its half-life of "only" 19 quintillion years.
Nuclear Physics scientists are currently searching for dark matter particles is located about 1,400 meters beneath the Gran Sasso massif, well protected from cosmic rays which can produce false signals. Theoretical considerations predict that dark matter should very rarely “collide” with the atoms of the detector.
This assumption is fundamental to the working principle of the XENON1T detector: its central part consists of a cylindrical tank of about one meter in length filled with 3,200 kilograms of liquid xenon at a temperature of –95° C.
When a dark matter particle interacts with a xenon atom, it transfers energy to the atomic nucleus which subsequently excites other xenon atoms. This leads to the emission of faint signals of ultraviolet light which are detected by means of sensitive light sensors located in the upper and lower parts of the cylinder. The same sensors also detect a minute amount of electrical charge which is released by the collision process.
The new study shows that the XENON1T detector is also able to measure other rare physical phenomena, such as double electron capture. To understand this process, one should know that an atomic nucleus normally consists of positively charged protons and neutral neutrons, which are surrounded by several atomic shells occupied by negatively charged electrons. Xenon-124, for example, has 54 protons and 70 neutrons.
In double electron capture, two protons in the nucleus simultaneously “catch” two electrons from the innermost atomic shell, transform into two neutrons, and emit two neutrinos.
The other atomic electrons reorganize themselves to fill in the two holes in the innermost shell. The energy released in this process is carried away by X-rays and so-called Auger electrons. However, these signals are very hard to detect, as double electron capture is a very rare process which is hidden by signals from the omnipresent natural radioactivity.
After sorting through a year's worth of data, researchers have now reported observing dozens of these kinds of decays. The event itself is known as electron capture, where an electron enters the nucleus of an atom and turns a proton into a neutron, which causes its decay. In this case, the researchers saw double electron captures for the first time.
