Physics

Dark matter detector reveals material with longest half-life ever – 18 sextillion years

Dark matter detector reveals m...
The XENON1T experiment may not have found dark matter, but it has now revealed the element with the longest half-life ever recorded
The XENON1T experiment may not have found dark matter, but it has now revealed the element with the longest half-life ever recorded
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Researchers Daniel Coderre (left) and Christopher Tunnell (right) 
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Researchers Daniel Coderre (left) and Christopher Tunnell (right) 
Study co-author Christopher Tunnell at the XENON1T experiment in Italy
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Study co-author Christopher Tunnell at the XENON1T experiment in Italy
The XENON1T experiment may not have found dark matter, but it has now revealed the element with the longest half-life ever recorded
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The XENON1T experiment may not have found dark matter, but it has now revealed the element with the longest half-life ever recorded
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Although the many experiments searching for evidence of dark matter have yet to turn up any solid proof of the stuff yet, they are making other amazing discoveries. 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.

Half-life is a measure of a material's stability, in terms of how long on average it's expected to take for half of its atoms to decay. 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 13.8 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.

Since it occurs on such an incredibly long timescale, the decay of these xenon atoms is an extremely rare event. But the more atoms you watch at once, the better your chances of seeing it happen. So if anything is going to spot it, the XENON1T experiment is, with 1,300 kg (2,866 lb) of liquid xenon in a tank and sensitive detectors set up to watch for photons and other particles emitted as a result of these events.

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.

Study co-author Christopher Tunnell at the XENON1T experiment in Italy
Study co-author Christopher Tunnell at the XENON1T experiment in Italy

"Normally, you have one electron come in and one neutrino come out," says Christopher Tunnell, co-author of the study. "That neutrino has a fixed energy, which is how the nucleus expels its mass. This is a process we see often in nuclear particle physics, and it's quite well understood. But we had never seen two electrons come into the nucleus at the same time and give off two neutrinos."

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, the elusive substance that appears to outnumber normal matter by more than five to one. It's thought that these experiments can help capture the rare times dark matter interacts with normal matter. While none have managed to do so yet, the data can lead to other observations, as the new study demonstrates.

The research was published in the journal Nature.

Source: Rice University

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8 comments
JasonButterworth
With such a long half life surely xenon 124 was around before or universe was born. Which makes me wonder what was there before the big bang?
DomainRider
@JasonButterworth - the half-life is not related to the time since the element was created, but is a constant that tells you how long it takes for half of a sample to decay; i.e. how stable the element is. So if you had a sample and waited until half of it had decayed (which would be a bit boring for xenon 124), would take the same amount of time again for half of what was left of it to decay.
Kpar
Jason, that's not quite the way it works. A half-life begins when the substance itself was created. This just shows that almost all of the Xe124 that was created in supernovae is still around.
Cryptonoetic
I cannot help but be amused that an ostensible 80% of all matter is everywhere but here.
txt295
The claim that "xenon-124 has the longest half-life ever measured in a material" (quoted from the article) is missleading, because there are much stabler materials than that. For example the ordinary iron-56 is observationally stable, but theoretically can decay to Cr⁵⁴, with a half-life of more than 3.1x10²² years via double electron capture (quote from WikiPedia). And for example tellurium-128 has the half-life of 2.2x10²⁴ which is two orders higher than the half-life mentioned in the article. As for bismuth-209 - it only has the longest known half-life of any radioisotope that undergoes α-decay, which does not mean that there are no elements with longer half-time, as the article suggests.
Rocky Stefano
@JasonButterworth - Likely alternate universes colliding to form new (big bang) galaxies.
RMM
Geez guys... the Universe is NOT 13.8 billion years old. That is applicable to the OBSERVABLE Universe. You really think that what you can "see" based on the speed of light is all there is to see? Perspective matters in all things matter.
galaxydrifter
Well I am no Scientist, but thats a lot of sex.