A dark-matter detector buried under 1500 metres of Italian mountain has recorded what is arguably the most uncommon phenomenon in the universe – the decay of a Xenon-124 atom.
All radioactive matter is measured by what is commonly called a “half-life”, which is defined as the time taken for half the radioactive atoms in any given sample to decay away.
Half-lives vary wildly, depending on the elements involved. Flerovium-289, for instance, has a half-life of just 2.6 seconds, while plutonium-239 takes 24,110 years to lose 50% of its load.
And although 24,000 years is a very long period of time – and one of the reasons the use of plutonium to generate electricity is viewed with caution – it is nothing, it turns out, compared to Xenon-124.
Italy’s Laboratori Nazionali del Gran Sasso (LNGS), deep beneath the Gran Sasso mountains, is a dark-matter detector that comprises a cylindrical tank filed with 3200 kilograms of liquid xenon at a temperature of minus-95 degrees Celsius.
The detector is completely sealed off from any possible radioactive interference, meaning that should a dark-matter particle ever crash into it the tiny signal generated will be clear and unambiguous.
Thus far, it has never happened.
However, researchers led by Christian Weinheimer of Germany’s University of Münster recently achieved some sort of consolation prize when they observed the decay of a Xenon-124 atom.
This occurred through a process called double electron capture. A Xenon-124 nucleus comprises 54 protons and 70 neutrons, which are surrounded by several shells made of negatively charged electrons.
Weinheimer and colleagues observed two protons in one such nucleus bond with a pair of electrons, which made the newly paired particles transform into neutrons, releasing two neutrinos as a result. The remaining electrons – now missing a couple – rearranged, emitting x-rays in the process.
The atom had decayed. It is a process the researchers have now recorded 126 times in the past two years – making it a very rare event indeed, given just how many Xenon-124 atoms comprise 3200 litres of the stuff.
How rare? Weinheimer and colleagues calculate the half-life of Xenon-124 to be 1.8 x 1022years – or several trillion years longer than the universe has existed.
The findings are contained in a paper in the journal Nature.
I'm an enthusiast deeply immersed in the field of particle physics and nuclear decay, with a focus on dark matter detection. My extensive knowledge in this area allows me to provide insights into the groundbreaking discoveries made by researchers at Italy’s Laboratori Nazionali del Gran Sasso (LNGS) regarding the decay of a Xenon-124 atom.
The experiment conducted at LNGS involves a sophisticated dark-matter detector located 1500 meters beneath the Gran Sasso mountains in Italy. This detector comprises a cylindrical tank filled with 3200 kilograms of liquid xenon maintained at a frigid temperature of minus-95 degrees Celsius. The crucial aspect of this setup is its complete isolation from any potential radioactive interference, ensuring that any signal generated is unequivocally attributed to the interaction with dark matter particles.
The observed phenomenon is the decay of a Xenon-124 atom, an event considered extremely rare in the realm of particle physics. The measurement of radioactive decay is commonly expressed through the concept of "half-life," defined as the time taken for half of the radioactive atoms in a sample to decay. In this case, the decay occurred through a process known as double electron capture.
Xenon-124, with its nucleus comprising 54 protons and 70 neutrons, experienced a unique transformation. Two protons within the nucleus bonded with a pair of electrons, converting into neutrons and releasing two neutrinos in the process. The rearrangement of the remaining electrons, now missing a couple, emitted x-rays, signifying the decay of the atom. Remarkably, researchers, led by Christian Weinheimer of Germany’s University of Münster, recorded this event 126 times in the past two years.
The rarity of this decay event is underscored by the calculated half-life of Xenon-124, an astounding 1.8 x 10^22 years. To put this in perspective, this is several trillion years longer than the age of the universe itself. The findings of this groundbreaking research have been documented in a paper published in the prestigious journal Nature.
This discovery not only expands our understanding of nuclear processes and rare decay events but also showcases the precision and capability of dark matter detectors in capturing elusive phenomena deep beneath the Earth's surface.
