Nuclear Reactor Mystery Solved, With No Need For New Particles (science.org) 33
sciencehabit shares a report from Science Magazine: A physics mystery has come to an end, with a resolution about as shocking as "the butler did it." For a decade, physicists have pondered why nuclear reactors pump out fewer particles called neutrinos than predicted. Some suggested the elusive bits of matter might be morphing into weirder, undetectable "sterile" neutrinos. Instead, new results pin down what other experiments had suggested: that theorists overestimated how many neutrinos a reactor should produce. [...]
In a reactor's core, uranium and plutonium nuclei split in a chain reaction, and the antineutrinos come from the radioactive "beta decay" of the lighter nuclei left behind. In such decay, a neutron in a nucleus changes into a proton while emitting an electron and an electron antineutrino. To predict the total flux of antineutrinos, physicists had to account for the amounts and decays of myriad different nuclei. That accounting pointed to a shortfall, but in 2017, physicists from the Daya Bay Reactor Neutrino Experiment in China called it into question. They studied antineutrinos from six commercial reactors, burning fuel with 4% uranium-235 atoms, which can sustain a chain reaction, and 96% uranium-238 atoms, which can't. As the uranium-235 is consumed, neutrons from its fission convert uranium-238 into plutonium-239, which also sustains a chain reaction. Daya Bay physicists found the antineutrino deficit shrank as the amount of uranium-235 fell, suggesting theorists had overestimated the flux of antineutrinos originating from uranium-235.
Now, physicists working at a small research reactor in France have confirmed that suspicion. The reactor at the Laue-Langevin Institute (ILL) produces copious neutrons for studies of materials. It also uses fuel containing 93% uranium-235. So, by studying the antineutrinos from it, researchers working with a neutrino detector called STEREO could measure the flux of antineutrinos from uranium-235 alone. The detector consists of six identical oil-filled segments lined up like teeth and spanning a distance of 9 to 11 meters from the reactor's core. Rarely, a proton in the oil will absorb an electron antineutrino to turn into a neutron while ejecting a positron -- sort of the reverse of beta decay. As the positron streaks through the oil, it produces light in proportion to the energy of the original neutrino. STEREO researchers showed the spectrum of energies of electron antineutrinos remained the same as distance from the core increased. That observation clashes with the idea that some are morphing into sterile neutrinos, because lower energy neutrinos should morph faster than higher energy ones, changing the spectrum as the neutrinos advance. STEREO researchers also showed the total flux of antineutrinos from uranium-235 was lower than the one used in theorists' models, as they report today in Nature. Taken together, the observations put an end to the reactor antineutrino deficit as evidence for a 1-eV sterile neutrino, says David Lhuillier, a neutrino physicist at France's Atomic Energy Commission and spokesperson for the 26-member STEREO team. "Can it be explained by a sterile neutrino of mass around 1 eV? The answer is no."
Other experiments -- such as one called PROSPECT at Oak Ridge National Laboratory -- had reached similar conclusions, Lhuillier notes.
In a reactor's core, uranium and plutonium nuclei split in a chain reaction, and the antineutrinos come from the radioactive "beta decay" of the lighter nuclei left behind. In such decay, a neutron in a nucleus changes into a proton while emitting an electron and an electron antineutrino. To predict the total flux of antineutrinos, physicists had to account for the amounts and decays of myriad different nuclei. That accounting pointed to a shortfall, but in 2017, physicists from the Daya Bay Reactor Neutrino Experiment in China called it into question. They studied antineutrinos from six commercial reactors, burning fuel with 4% uranium-235 atoms, which can sustain a chain reaction, and 96% uranium-238 atoms, which can't. As the uranium-235 is consumed, neutrons from its fission convert uranium-238 into plutonium-239, which also sustains a chain reaction. Daya Bay physicists found the antineutrino deficit shrank as the amount of uranium-235 fell, suggesting theorists had overestimated the flux of antineutrinos originating from uranium-235.
Now, physicists working at a small research reactor in France have confirmed that suspicion. The reactor at the Laue-Langevin Institute (ILL) produces copious neutrons for studies of materials. It also uses fuel containing 93% uranium-235. So, by studying the antineutrinos from it, researchers working with a neutrino detector called STEREO could measure the flux of antineutrinos from uranium-235 alone. The detector consists of six identical oil-filled segments lined up like teeth and spanning a distance of 9 to 11 meters from the reactor's core. Rarely, a proton in the oil will absorb an electron antineutrino to turn into a neutron while ejecting a positron -- sort of the reverse of beta decay. As the positron streaks through the oil, it produces light in proportion to the energy of the original neutrino. STEREO researchers showed the spectrum of energies of electron antineutrinos remained the same as distance from the core increased. That observation clashes with the idea that some are morphing into sterile neutrinos, because lower energy neutrinos should morph faster than higher energy ones, changing the spectrum as the neutrinos advance. STEREO researchers also showed the total flux of antineutrinos from uranium-235 was lower than the one used in theorists' models, as they report today in Nature. Taken together, the observations put an end to the reactor antineutrino deficit as evidence for a 1-eV sterile neutrino, says David Lhuillier, a neutrino physicist at France's Atomic Energy Commission and spokesperson for the 26-member STEREO team. "Can it be explained by a sterile neutrino of mass around 1 eV? The answer is no."
Other experiments -- such as one called PROSPECT at Oak Ridge National Laboratory -- had reached similar conclusions, Lhuillier notes.
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There are many mysteries. I think the biggest one is why we don't have thorium reactors yet!
Wind and solar are cheaper.
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come back and try to say that in two years.
well, dumber countries still won't have thorium reactors, true, but..
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You get what you pay for.
But wind and solar don't pay for anything. When issues of storage and delivery guarantees come up, they just look around to see who they can stick with the bill.
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There are many mysteries. I think the biggest one is why we don't have thorium reactors yet!
Wind and solar are cheaper.
Yeah but we should still build enough thorium reactors to re-process the existing stockpiles of spent fuel down to a much smaller and easier to manage volume.
Just as a way to save money on long-term storage it is great idea.
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Thorium reactors are a bust. Every attempt to build one has ended in some kind of failure, and they will never be commercially viable. It's cheaper to stick the waste in the ground.
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Uh, did anyone RTFA? No mystery was solved. One possible solution was discarded because it appears the "missing" neutrinos did not oscillate to an alternate form. One fallback solution is that the original model for fission was wrong but the current result does not actually strengthen evidence for that solution. TLDR: NoQED
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Yes, but at least this isn't a dumbed down topic.
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Yeah but we should still build enough thorium reactors to re-process the existing stockpiles of spent fuel down to a much smaller and easier to manage volume.
If you knew how to do that, and could explain it in a way that it can be implemented, you certainly receive a Nobel Prize!! Go Go!
Reprocessing spent nuclear fuel in a Thorium reactor - which science fiction journal did you read?
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In this particular case , it looks more like the victim tripped over while running with scisors.
Turns out nobody was the murderer in the case of the missing neutrinos!
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It was Colonel Meson, in the High Energy Physics Laboratory, with ... what else... a Candlestick.
I think the missing particles jumped to another Universe through a hole in the Cosmic Border Fence that was left unbuilt.
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While I realise your just trying to make a weak troll, literally nobody sensible in phyiscs believes that the Standard Model, nor any of its less hetrodox deviations is "settled science" (Unlike CO2 Climate change , for which the evidence is beyond overwhelming), its just the best theory we have at the moment.
What is it with anti-science people on this supposedly "news for nerds" site?
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But solving those problems would not destroy the Standard Model. Probably ca
Sucks (Score:4, Funny)
I hate it when science mysteries are solved. Fuck you standard model! Fuck you relativity!
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My beef with solved physics is its looking increasingly like the whole "lets go to spaaaaaaaace" star trek things probably gonna be a bust thanks to that *awful bully* Einstein and his speed of light thing.
Boo Mr Einstein!. I wanna meet Mr Spock!
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star trek things probably gonna be a bust thanks to that *awful bully* Einstein and his speed of light thing.
Boo Mr Einstein!. I wanna meet Mr Spock!
Only a problem if you need to come back and boast to your friends about all the alien females you nailed. Relativistic time dilation and/or suspended animation make visiting other worlds possible.
My bigger beef is with Comrade Tsiolkovsky and his Rocket Equation.
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I hate it when science mysteries are solved.
Not much of a mystery: our calculation don't work out, so either there is an entirely new particle, or our figures are wrong. No prozes for gussing which.
Null results are useful but I can't get excited about them.
In other news: charge of the neutron stll zero.
Missing mass discovered down the back of the sofa.
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No prozes for gussing which
But do I get a prize for guessing that you haven't gotten used to the placement of the e and i keys on your keyboard?
Max Planck wins again (Score:2)
Paraphrase: "Science marches forward one, dead, over-rated scientist at a time."
Some highly rated scientist said Uranium decay produces X neutrinos, and no one wanted to call them out for being wrong. So now, years later, we finally experiment to prove them wrong.