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Old 5th March 2019, 10:53 AM   #1
JeanTate
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Russian and Japanese neutrino detectors, "deficit"?

In a discussion of some pseudo-science (holler if you'd like the source), I came across this:
Quote:
Russia built two detectors with gallium and Japan built detectors using water and heavy water. Each detector had a characteristic range of neutrinos it could observe. But in all cases, there was a serious discrepancy between theory and reality.

The neutrino deficit remained on the order of 60%.
In context, the "neutrino deficit" refers to the solar neutrino deficit, between the flux predicted by standard solar models and that observed here on (or under) Earth.

Does anyone know what "detectors" (or experiments) are being referred to? I certainly do not.
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Old 5th March 2019, 12:28 PM   #2
RecoveringYuppy
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SAGE is the Russian-American one.


ETA: https://en.wikipedia.org/wiki/SAGE_(...um_Experiment)
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Old 5th March 2019, 01:10 PM   #3
JeanTate
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Originally Posted by RecoveringYuppy View Post
SAGE is the Russian-American one.


ETA: https://en.wikipedia.org/wiki/SAGE_(...um_Experiment)
Thanks!

Now I know where to look for the relevant papers.

I certainly know of Japanese experiments which sorta fit the description ... except for the "serious discrepancy between theory and reality". In fact, one such (Super-Kamiokande) demonstrated "atmospheric" neutrino oscillations, while confirming the "deficit" of electron neutrinos (Takaaki Kajita shared the 2015 Physics Nobel for the Super-K work).
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Old 5th March 2019, 02:13 PM   #4
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I might have this wrong, but I once read that a seriously large deficit in the level of solar neutrinos detected as (compared with the level that would be expected by theory) indicates that the solar core is not as active as theory predicts. AIUI neutrinos from the core come to us directly with a travel time of 8 minutes, while photons from the core take hundreds, perhaps thousands of years to make the trip before speeding the last 8 minutes to Earth.

If this is correct, then the question may be... is our model/theory/understanding wrong and the level of neutrinos has always been this low, or is the sun's core becoming less active and we haven't yet seen the result of that in its light output?

If the latter is true, then that could be quite a scary scenario, because the low end of the theorised time for photons from the core to reach the surface is less than 300 years.
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Old 5th March 2019, 02:30 PM   #5
JeanTate
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Originally Posted by smartcooky View Post
I might have this wrong, but I once read that a seriously large deficit in the level of solar neutrinos detected as (compared with the level that would be expected by theory) indicates that the solar core is not as active as theory predicts. AIUI neutrinos from the core come to us directly with a travel time of 8 minutes, while photons from the core take hundreds, perhaps thousands of years to make the trip before speeding the last 8 minutes to Earth.

If this is correct, then the question may be... is our model/theory/understanding wrong and the level of neutrinos has always been this low, or is the sun's core becoming less active and we haven't yet seen the result of that in its light output?

If the latter is true, then that could be quite a scary scenario, because the low end of the theorised time for photons from the core to reach the surface is less than 300 years.
Indeed, that was one idea put forward to explain the "solar neutrino problem". Before the Sudbury Neutrino Observatory and Super-K results ... neutrino oscillation (many experimental confirmations) now explains the apparent deficit, and standard solar models were right all along (modulo the incremental improvements that happen all the time).
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Old 5th March 2019, 02:38 PM   #6
BowlOfRed
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Originally Posted by smartcooky View Post
If the latter is true, then that could be quite a scary scenario, because the low end of the theorised time for photons from the core to reach the surface is less than 300 years.
While it's true that the sun is so dense that the mean time for the energy of a photon (not the photon itself) to reach the surface is enormous (more like 100 000 years), it's not true that we'd have to wait that long to see any effects of changes in the core.

Changes in the core would affect the pressure there, and that would be transmitted through the sun at the speed of sound.
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Old 5th March 2019, 03:11 PM   #7
RecoveringYuppy
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Originally Posted by BowlOfRed View Post
Changes in the core would affect the pressure there, and that would be transmitted through the sun at the speed of sound.

Also, that speed of sound would be much faster than the speed of sound in air we're used to on Earth due the density you mentioned.
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Last edited by RecoveringYuppy; 5th March 2019 at 04:00 PM. Reason: correct typo
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Old 5th March 2019, 03:46 PM   #8
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Old 5th March 2019, 04:12 PM   #9
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I would also add that the surface of the sun isn't heated only via those photons that get absorbed and reemitted. There's quite a lot of plain ol' convection going on. So we'd notice it a lot sooner than those hundreds of years.

Plus, we'd need to rewrite not just nuclear physics, but also our understanding of plain ol' fluids, if that were the case. The sun currently has about two million convective "cells", each about 1500 km across. A red giant, which is cooler, might have as little as a few dozen cells, although they're much larger. It would be fairly hard to explain what's happening there, if there were 60% less energy driving that convection.
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Old 5th March 2019, 04:14 PM   #10
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Also, just to make it clear what is being transmitted at sound speed: the colossal weight of the sun is supported by radiation pressure from inside. Less pressure, things start to compress under their own weight. So we'd see a very different density of the Sun.
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