Nav: Home

Researchers observe slowest atom decay ever measured

April 24, 2019

Around 1500 meters deep in the Italian Gran Sasso mountains is the underground laboratory LNGS (Laboratori Nazionali del Gran Sasso), in which scientists search for dark matter particles in a lab sealed off from any radioactivity interference. Their tool is the XENON1T detector, the central part of which consists of a cylindrical tank of about one meter in length filled with 3200 kilograms of liquid xenon at a temperature of -95 degrees Celsius.

The rarest decay process ever measured

Until now, researchers using this detector have not yet observed any dark matter particles, but they have now managed to observe the decay of the Xenon-124 atom for the first time. The half-life time measured - i.e. the time span after which half of the radioactive atoms originally present in a sample have decayed away - is over a trillion times longer than the age of the universe, which is almost 14 billion years old. The observed process is therefore the rarest process in the universe ever to be directly seen happening in a detector. "The fact that we managed to directly observe this process demonstrates how powerful our detection method actually is - also for rare physical phenomena which are not from dark matter," says Professor Laura Baudis, astroparticle physicist at the University of Zurich, who is one of the leading scientists on the XENON1T experiment.

A phenomenon that is hard to demonstrate

The observed process is called a double electron capture: The atomic nucleus of Xenon-124 consists of 54 positively charged protons and 70 neutral neutrons, which are surrounded by several atomic shells occupied by negatively charged electrons. 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. As two electrons are then missing in the atomic shell, the other electrons reorganize themselves, with the energy released being carried away by X-rays. However, this is a very rare process which is usually hidden by signals from the omnipresent "normal" radioactivity - in the sealed-off environment of the underground laboratory, however, it has now been possible to observe the process.

Calculating half-life time from light signals

The X-rays from the double electron capture produced an initial light signal as well as free electrons in the liquid xenon of the XENON1T detector. The electrons were moved toward the upper part of the detector where they generated a second light signal. From the direction and the time difference between the two signals, the researchers could determine the exact position of the double electron capture and the energy released during the decay. From the 126 processes observed in total over the last two years, the physicists calculated the enormously long half-life of 1.8 x 10 high 22 years for the atom Xenon-124. That is the slowest process ever measured directly.

"The new results show how well the XENON1T detector can detect very rare processes and reject background signals," says Laura Baudis. While two neutrinos are emitted in the double electron capture process, scientists can now also search for the so-called neutrino-less double electron capture which could shed light on important questions regarding the nature of neutrinos.
-end-
Literature: E. Aprile et al. First observation of two-neutrino double electron capture in 124Xe with XENON1T. Nature. 24 April 2019. DOI: 10.1038/s41586-019-1124-4

The XENON1T experiment

With the XENON1T detector, physicists originally wanted to detect dark matter particles. Theoretical considerations predict that dark matter should very rarely "collide" with a xenon atom in the tank of the detector which is filled with liquid xenon. It thereby transfers energy to the atomic nucleus which subsequently excites other xenon atoms and causes them to emit light. These very faint signals of ultraviolet light and the minute amount of electrical charge which is released by the collision process are detected by means of sensitive light sensors. The detector was switched off for upgrading in 2018: The three times larger active detector mass along with further modifications will boost the new XENONnT detector's sensitivity considerably.

The XENON1T detector is an international project involving around 160 researchers. In Switzerland the experiment receives funding from the SNSF and the University of Zurich. International support comes from Germany, the USA, Italy, Israel, Portugal, France, Sweden, the Netherlands and from the European Union.

University of Zurich

Related Dark Matter Articles:

A new approach to the hunt for dark matter
A study that takes a novel approach to the search for dark matter has been performed by the BASE Collaboration at CERN working together with a team at the PRISMA+ Cluster of Excellence at Johannes Gutenberg University Mainz (JGU).
Could the mysteries of antimatter and dark matter be linked?
RIKEN researchers and collaborators have performed the first laboratory experiments to determine whether a slightly different way in which matter and antimatter interact with dark matter might be a key to solving both mysteries.
Placing another piece in the dark matter puzzle
A team led by Prof Dmitry Budker has continued their search for dark matter within the framework of the 'Cosmic Axion Spin Precession Experiment' (or 'CASPEr' for short).
Physicists have found a way to 'hear' dark matter
Physicists at Stockholm University and the Max Planck Institute for Physics have turned to plasmas in a proposal that could revolutionise the search for the elusive dark matter.
New hunt for dark matter
Dark matter is only known by its effect on massive astronomical bodies, but has yet to be directly observed or even identified.
Tracking down dark matter
Over time, scientists have developed different theories to explain exactly what the mysterious dark matter might be made of.
A new candidate for dark matter and a way to detect it
Two theoretical physicists at UC Davis have a new candidate for dark matter and a possible way to detect it.
The mystery of the galaxy with no dark matter: Solved!
A group of researchers from the Instituto de Astrofísica de Canarias (IAC) has clarified one of the mysteries of 2018 in the field of extragalactic astrophysics: the supposed existence of a galaxy without dark matter.
Physicists constrain dark matter
Researchers from Russia, Finland, and the U.S. have put a constraint on the theoretical model of dark matter particles by analyzing data from astronomical observations of active galactic nuclei.
Dark matter on the move
Scientists have found evidence that dark matter can be heated up and moved around, as a result of star formation in galaxies.
More Dark Matter News and Dark Matter Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

Risk
Why do we revere risk-takers, even when their actions terrify us? Why are some better at taking risks than others? This hour, TED speakers explore the alluring, dangerous, and calculated sides of risk. Guests include professional rock climber Alex Honnold, economist Mariana Mazzucato, psychology researcher Kashfia Rahman, structural engineer and bridge designer Ian Firth, and risk intelligence expert Dylan Evans.
Now Playing: Science for the People

#541 Wayfinding
These days when we want to know where we are or how to get where we want to go, most of us will pull out a smart phone with a built-in GPS and map app. Some of us old timers might still use an old school paper map from time to time. But we didn't always used to lean so heavily on maps and technology, and in some remote places of the world some people still navigate and wayfind their way without the aid of these tools... and in some cases do better without them. This week, host Rachelle Saunders...
Now Playing: Radiolab

Dolly Parton's America: Neon Moss
Today on Radiolab, we're bringing you the fourth episode of Jad's special series, Dolly Parton's America. In this episode, Jad goes back up the mountain to visit Dolly's actual Tennessee mountain home, where she tells stories about her first trips out of the holler. Back on the mountaintop, standing under the rain by the Little Pigeon River, the trip triggers memories of Jad's first visit to his father's childhood home, and opens the gateway to dizzying stories of music and migration. Support Radiolab today at Radiolab.org/donate.