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Scientists see 'rarest event ever recorded' in search for dark matter

The team caught a glimpse of a process that takes 18,000,000,000,000,000,000,000 years.

Image source: Pixabay
  • In Italy, a team of scientists is using a highly sophisticated detector to hunt for dark matter.
  • The team observed an ultra-rare particle interaction that reveals the half-life of a xenon-124 atom to be 18 sextillion years.
  • The half-life of a process is how long it takes for half of the radioactive nuclei present in a sample to decay.

Scientists have observed an extremely rare particle physics event using a detector that's hunting for dark matter, the mysterious material that physicists have yet to observe.

In a paper published in the journal Nature, researchers with the XENON Collaboration said they'd observed the radioactive decay of a substance called xenon-124, an isotope of the element xenon — a colorless and odorless noble gas found in tiny amounts in the atmosphere. The event — a "two-neutrino double electron capture" — has eluded scientists for decades.

It happens when "two protons in a nucleus are simultaneously converted into neutrons by the absorption of two electrons from one of the atomic shells and the emission of two electron neutrinos." After this occurs, the event shoots out a predictable cascade of X-rays and Auger electrons that scientists look for using an ultra-sensitive detector, buried about 5,000 feet beneath Italy's Gran Sasso mountain where it's shielded from cosmic rays.

"We have shown that we can observe the rarest events ever recorded," Ethan Brown, a professor of physics at Rensselaer Polytechnic Institute and co-author of the study, told Newsweek. "The key finding is that an isotope formerly thought to be completely stable has now been shown to decay on an unimaginably long timescale."

How long is that timescale? The team estimated that xenon-124's half-life is about 18 sextillion years — or 18,000,000,000,000,000,000,000 years — which is than one trillion times the age of our universe, according to the team. It's the slowest process ever measured directly, the team wrote in a statement.

"It's an amazing to have witnessed this process, and it says that our detector can measure the rarest thing ever recorded," Brown told The Independent.

"We designed the XENON1T experiment to look for dark matter, a new kind of matter that makes up 85 percent of the mass of the universe, but interacts so rarely that it's never been observed," Brown said. "This experiment is so sensitive to very rare events that we can make all kinds of other rare physics measurements. One of those is this decay of xenon-124. Although our primary goal was always the discovery of dark matter, we knew there was a good chance we could see this rare decay, so we set out to do so."

To get that good chance, the team had to expose their detector to a huge amount of xenon atoms by stocking it with 3.2 tons worth of liquid xenon.

"XENON1T is a giant vat of liquid xenon surrounded by light sensors," Brown said. "When dark matter collides in the xenon, or when a radioactive decay occurs inside, we get a tiny flash of light and a little bunch of charge out of the xenon. We measure these with the light sensors and reconstruct everything we can about the original event that caused the light and charge."

Although the team didn't observe dark matter — which is the primary purpose of the detector — the recent observations could help scientists learn more about neutrinos, one of the least understood fundamental particles in the universe.

"It proves that this XENON detector technology we use for dark matter is much more versatile," graduate student Christian Wittweg, Ph.D student at the University of Münster in Germany, told Gizmodo. "We get all these cool analyses... for free after having built an experiment sensitive enough to hunt for dark matter."

The team plans to use its newer XENONnT detector to continue hunting for dark matter, the elusive material that's estimated to comprise about 26.8 percent of all the content in the universe.

Neom, Saudi Arabia's $500 billion megacity, reaches its next phase

Construction of the $500 billion dollar tech city-state of the future is moving ahead.

Credit: Neom
Technology & Innovation
  • The futuristic megacity Neom is being built in Saudi Arabia.
  • The city will be fully automated, leading in health, education and quality of life.
  • It will feature an artificial moon, cloud seeding, robotic gladiators and flying taxis.
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Tuberculosis vaccine shows promise in reducing COVID deaths

A new study suggests that a century-old vaccine may reduce the severity of coronavirus cases.

Closeup of a BCG vaccination.

Credit: Kekyalyaynen.
Surprising Science
  • A new study finds a country's BCG vaccination is linked to its COVID-19 mortality rate.
  • More BCG vaccinations is linked to fewer severe coronavirus cases.
  • The study is preliminary and more research is needed to support the findings.
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Human brains remember certain words more easily than others

A study of the manner in which memory works turns up a surprising thing.

Image Point Fr / Shutterstock
Mind & Brain
  • Researchers have found that some basic words appear to be more memorable than others.
  • Some faces are also easier to commit to memory.
  • Scientists suggest that these words serve as semantic bridges when the brain is searching for a memory.

Cognitive psychologist Weizhen Xie (Zane) of the NIH's National Institute of Neurological Disorders and Stroke (NINDS) works with people who have intractable epilepsy, a form of the disorder that can't be controlled with medications. During research into the brain activity of patients, he and his colleagues discovered something odd about human memory: It appears that certain basic words are consistently more memorable than other basic words.

The research is published in Nature Human Behaviour.

An odd find

Image source: Tsekhmister/Shutterstock

Xie's team was re-analyzing memory tests of 30 epilepsy patients undertaken by Kareem Zaghloul of NINDS.

"Our goal is to find and eliminate the source of these harmful and debilitating seizures," Zaghloul said. "The monitoring period also provides a rare opportunity to record the neural activity that controls other parts of our lives. With the help of these patient volunteers we have been able to uncover some of the blueprints behind our memories."

Specifically, the participants were shown word pairs, such as "hand" and "apple." To better understand how the brain might remember such pairings, after a brief interval, participants were supplied one of the two words and asked to recall the other. Of the 300 words used in the tests, five of them proved to be five times more likely to be recalled: pig, tank, doll, pond, and door.

The scientists were perplexed that these words were so much more memorable than words like "cat," "street," "stair," "couch," and "cloud."

Intrigued, the researchers looked at a second data source from a word test taken by 2,623 healthy individuals via Amazon's Mechanical Turk and found essentially the same thing.

"We saw that some things — in this case, words — may be inherently easier for our brains to recall than others," Zaghloul said. That the Mechanical Turk results were so similar may "provide the strongest evidence to date that what we discovered about how the brain controls memory in this set of patients may also be true for people outside of the study."

Why understanding memory matters

person holding missing piece from human head puzzle

Image source: Orawan Pattarawimonchai/Shutterstock

"Our memories play a fundamental role in who we are and how our brains work," Xie said. "However, one of the biggest challenges of studying memory is that people often remember the same things in different ways, making it difficult for researchers to compare people's performances on memory tests." He added that the search for some kind of unified theory of memory has been going on for over a century.

If a comprehensive understanding of the way memory works can be developed, the researchers say that "we can predict what people should remember in advance and understand how our brains do this, then we might be able to develop better ways to evaluate someone's overall brain health."

Party chat

Image source: joob_in/Shutterstock

Xie's interest in this was piqued during a conversation with Wilma Bainbridge of University of Chicago at a Christmas party a couple of years ago. Bainbridge was, at the time, wrapping up a study of 1,000 volunteers that suggested certain faces are universally more memorable than others.

Bainbridge recalls, "Our exciting finding is that there are some images of people or places that are inherently memorable for all people, even though we have each seen different things in our lives. And if image memorability is so powerful, this means we can know in advance what people are likely to remember or forget."

spinning 3D model of a brain

Temporal lobes

Image source: Anatomography/Wikimedia

At first, the scientists suspected that the memorable words and faces were simply recalled more frequently and were thus easier to recall. They envisioned them as being akin to "highly trafficked spots connected to smaller spots representing the less memorable words." They developed a modeling program based on word frequencies found in books, new articles, and Wikipedia pages. Unfortunately, the model was unable to predict or duplicate the results they saw in their clinical experiments.

Eventually, the researchers came to suspect that the memorability of certain words was linked to the frequency with which the brain used them as semantic links between other memories, making them often-visited hubs in individuals's memory networks, and therefore places the brain jumped to early and often when retrieving memories. This idea was supported by observed activity in participants' anterior temporal lobe, a language center.

In epilepsy patients, these words were so frequently recalled that subjects often shouted them out even when they were incorrect responses to word-pair inquiries.

Seek, find

Modern search engines no longer simply look for raw words when resolving an inquiry: They also look for semantic — contextual and meaning — connections so that the results they present may better anticipate what it is you're looking for. Xie suggests something similar may be happening in the brain: "You know when you type words into a search engine, and it shows you a list of highly relevant guesses? It feels like the search engine is reading your mind. Well, our results suggest that the brains of the subjects in this study did something similar when they tried to recall a paired word, and we think that this may happen when we remember many of our past experiences."

He also notes that it may one day be possible to leverage individuals' apparently wired-in knowledge of their language as a fixed point against which to assess the health of their memory and brain.

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