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Thread: Neutrinos?

  1. #1 Neutrinos? 
    Forum Freshman LotusTiger's Avatar
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    Are there theories for why that is neutrinos move through material bodies? Is it there are any patterns for why they move through matter too?


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    Neutrinos interact through the weak nuclear force. They have two things going against them, the weaknesss of the WEAK nuclear force and the short range of the weak nuclear force.


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    Quote Originally Posted by MigL View Post
    Neutrinos interact through the weak nuclear force. They have two things going against them, the weaknesss of the WEAK nuclear force and the short range of the weak nuclear force.
    I do not think that answers the question.
    For little I know, also neutrons interact weakly ( if they interact at all) and yet, cannot pass undisturbed through mass.

    If we consider that neutrino mass is valued (1/ million th) the electron mass, we might infer that probably its radius is only 2 orders (let's say up to 4 !!) smaller then electron or neutron.

    Supposing there is NO interaction whatsoever, it is still a huge problem to explain (if by nothing else) by probability
    how it can slip unnoticed through a planet.
    Last edited by peterpan; July 20th, 2011 at 03:12 AM.
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  5. #4  
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    Neutrinos pass through matter easily, since matter (on earth) is mostly empty space.
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    Quote Originally Posted by mathman View Post
    Neutrinos pass through matter easily, since matter (on earth) is mostly empty space.
    Not just matter on Earth, but matter everywhere is mostly empty space!
    "Nature doesn't care what we call it, she just does it anyway" - R. Feynman
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    Quote Originally Posted by x(x-y) View Post
    Quote Originally Posted by mathman View Post
    Neutrinos pass through matter easily, since matter (on earth) is mostly empty space.
    Not just matter on Earth, but matter everywhere is mostly empty space!
    Not completely true - how about neutron stars?
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    [QUOTE=mathman;275588
    Not completely true - how about neutron stars?[/QUOTE]

    quite right! what about black holes?
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    Quote Originally Posted by mathman View Post
    Quote Originally Posted by x(x-y) View Post
    Quote Originally Posted by mathman View Post
    Neutrinos pass through matter easily, since matter (on earth) is mostly empty space.
    Not just matter on Earth, but matter everywhere is mostly empty space!
    Not completely true - how about neutron stars?
    Yes, I suppose you're correct in saying that- but I was thinking of "matter" as in atoms (i.e. the constituents of matter), which are most certainly mostly empty space.

    Quote Originally Posted by peterpan View Post
    quite right! what about black holes?
    Black holes are not necessarily made up of matter- they are gravitational singularities which take in matter, however we do not know what is behind the event horizon of black holes; and so we don't actually know what a black hole is really made of, and, unfortunately, probably never will due to the nature of the event horizon- the "escape velocity" from inside the boundary of the event horizon exceeds the speed of light.
    "Nature doesn't care what we call it, she just does it anyway" - R. Feynman
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    The difference is that the weak nuclear force only has a specific ( atomic diameter ) range after which if falls to zero. This is because it is propagated by bosons which have appreciable mass ( +/-W and Z ) and which move at speeds much slower than c. Electromagnetic force and gravity are true long range forces which fall off with the square of the distance, but never actually become zero ( although EMF can be nullified because of opposing charges ).
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  11. #10  
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    Quote Originally Posted by peterpan View Post
    Quote Originally Posted by MigL View Post
    Neutrinos interact through the weak nuclear force. They have two things going against them, the weaknesss of the WEAK nuclear force and the short range of the weak nuclear force.
    I do not think that answers the question.
    For little I know, also neutrons interact weakly ( if they interact at all) and yet, cannot pass undisturbed through mass.

    If we consider that neutrino mass is valued (1/ million th) the electron mass, we might infer that probably its radius is only 2 orders (let's say up to 4 !!) smaller then electron or neutron.

    Supposing there is NO interaction whatsoever, it is still a huge problem to explain (if by nothing else) by probability
    how it can slip unnoticed through a planet.

    In order for an electron-neutrino to interact with matter it has to directly interact with a nucleon (tau and muon neutrinos only interact with their counterparts). The property that determines whether or not a neutrino will interact with a nucleon called its "cross section" , this is dependent with on its energy. The cross section of a neutrino produced by beta decay is ~ 10-43 cm2 .

    If you take this value and say the number of nucleons per cc of lead, you can calculate how far a neutrino would travel before it had a good chance of "striking" a nucleon. This the "free path" of the neutrino. For lead this turns out to be ~ 1 light year. In other words, the average neutrino could travel one light year of lead before hitting a nucleon.

    The only way to detect a neutrino is is by its interaction with a nucleon. So the vast majority of neutrinos pass through the Earth unnoticed because they do not interact with a nucleon.
    "Men are apt to mistake the strength of their feelings for the strength of their argument.
    The heated mind resents the chill touch & relentless scrutiny of logic"-W.E. Gladstone


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    Quote Originally Posted by JANUS View Post
    .1) The cross section of a neutrino produced by beta decay is ~ 10-43 cm2 .

    2) The only way to detect a neutrino is is by its interaction with a nucleon. .

    1) can you say something about a) how do you determine a cross-section, b) its size/radius
    2)do you mean that it can interact also with a neutron?
    3)could an X-ray produce directly neutrino+antineutrino?
    Last edited by phyz; July 24th, 2011 at 04:49 AM.
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    Forum Radioactive Isotope MagiMaster's Avatar
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    Be careful with 1b there. Just because it's called a cross section doesn't necessarily mean that it means the same thing as the cross section of a macroscopic object.
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    Quote Originally Posted by MagiMaster View Post
    Be careful with 1b there. Just because it's called a cross section doesn't necessarily mean that it means the same thing as the cross section of a macroscopic object.
    hi,
    I gave a look at your career to cosmic wizard, to your prievious posts and noticed that

    1) they average a couple of lines. Aren't you able to articulate more than a couple of sentences?, could you sometime do develop a
    discourse ? (wikictionary #3 in case you don't understant)
    2) You (either do not fully comprehend plain Englich, which I exclude, or) do not quote and then twist posters' words making incoherent conclusion and
    remarks.( to refresh your memory read Jagella's refuting of your post in 'a thought on mass...'
    3) who told you that 1b whas explaining 1a? your magipowers?
    4) Why don't you try sometime, at least once, to give a decent reply, an explanation, a piece of correct information?
    5) I f you are so wise, why don't you answer 1b ? and then 1a, and then..... and then ......
    6) Please refrain in future to chirp in in my posts, if you can only post press-releases from Your Masterness!

    * (sutor, ne ultra crepidam!) (*I completed Wikipidia's entry so that you can comprehend!)
    Last edited by phyz; July 29th, 2011 at 01:44 AM.
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  15. #14  
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    Quote Originally Posted by phyz View Post
    Quote Originally Posted by JANUS View Post
    .1) The cross section of a neutrino produced by beta decay is ~ 10-43 cm2 .

    2) The only way to detect a neutrino is is by its interaction with a nucleon. .

    1) can you say something about a) how do you determine a cross-section, b) its size/radius
    How far off the bullseye it can get without missing. One way of detecting them is to get a huge vat of water, and watch for Cherenkov Radiation created when a neutrino strikes the water nuclei.

    Neutrino detector - Wikipedia, the free encyclopedia

    Quote Originally Posted by Wiki Article
    Two water-filled detectors of this type (Kamiokande and IMB) recorded the neutrino burst from supernova 1987A.[6] According to one account, scientists detected only 19 neutrinos from an explosion of a star inside the Large magellanic Cloud -- only 19 out of a billion trillion trillion trillion trillion neutrinos which "flew from the supernova," according to one account.[1] Kamiokande was able to detect the burst of neutrinos associated with this supernova, and in 1988 it was used to directly confirm the production of solar neutrinos. The largest such detector is the water-filled Super-Kamiokande. This detector uses 50,000 tons of pure water surrounded by 11,000 photomultiplier tubes buried 1 km underground.
    That should give you some idea of how hard it is for them to randomly hit.

    2)do you mean that it can interact also with a neutron?
    Good question. I don't know if it can interact with a neutron directly, but it can interact with a proton and create a neutron. (Actually it creates a Neutron and a Positron)
    Cowan?Reines neutrino experiment - Wikipedia, the free encyclopedia
    3)could an X-ray produce directly neutrino+antineutrino?
    I don't know that either. I guess we'll only find out if someone manages to get a pair of them to annihilate. I can only imagine how difficult it would be to try and get a pair of them to hit each other.
    Some clocks are only right twice a day, but they are still right when they are right.
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    Quote Originally Posted by kojax View Post
    Quote Originally Posted by phyz View Post
    Quote Originally Posted by JANUS View Post
    1) One way of detecting them is to get a huge vat of water, and watch for Cherenkov Radiation created when a neutrino strikes the water nuclei.
    2)do you mean that it can interact also with a neutron?
    Good question. I don't know if it can interact with a neutron directly,
    but it can interact with a proton and create a neutron.
    3)could an X-ray produce directly neutrino+antineutrino?
    I don't know that either. I guess we'll only find out if someone manages to get a pair of them to annihilate. I can only imagine how difficult it would be to try and get a pair of them to hit each other.
    Thank you Sir,
    for your kind, clear, honest direct answers.
    at long last! .

    1), 2) that is the point ! what you detect in water is that there has happened a pair production
    That is only the effect,
    the causes can be many. A gamma ray hitting a nucleus produce the same effect.How can you affirm it was a neutrino?
    3)thank you for your frankness. But do you really think they could annihilate?
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  17. #16  
    Forum Radioactive Isotope MagiMaster's Avatar
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    Quote Originally Posted by phyz View Post
    Quote Originally Posted by MagiMaster View Post
    Be careful with 1b there. Just because it's called a cross section doesn't necessarily mean that it means the same thing as the cross section of a macroscopic object.
    hi,
    I gave a look at your career to cosmic wizard, to your prievious posts and noticed that

    1) they average a couple of lines. Aren't you able to articulate more than a couple of sentences?, could you sometime do develop a
    discourse ? (wikictionary #3 in case you don't understant)
    2) You (either do not fully comprehend plain Englich, which I exclude, or) do not quote and then twist posters' words making incoherent conclusion and
    remarks.( to refresh your memory read Jagella's refuting of your post in 'a thought on mass...'
    3) who told you that 1b whas explaining 1a? your magipowers?
    4) Why don't you try sometime, at least once, to give a decent reply, an explanation, a piece of correct information?
    5) I f you are so wise, why don't you answer 1b ? and then 1a, and then..... and then ......
    6) Please refrain in future to chirp in in my posts, if you can only post press-releases from Your Masterness!

    * (sutor, ne ultra crepidam!) (*I completed Wikipidia's entry so that you can comprehend!)
    Wow. That may be one of the most arrogant posts I've ever read.

    Let me try writing in a way you'll understand (a long numbered list of very short points).
    1) I try and keep my posts short and simple to keep them understandable.
    1a) When I have more to say, I say it.
    1b) When I don't know an answer, I don't bother to say anything.
    2) I apparently understand English better than you
    2a) I try hard not to twist others words. If I've misunderstood something, feel free to point that out.
    3) This may be a case where I misread.
    3a) The right thing to do would be to point out that I misread.
    4) My reply is still correct, even if it might not be strictly on topic.
    4a) Go reread some of my other posts.
    5) I don't answer because I don't know the answer. I'll freely admit that.
    5a) Just because I don't know the answer doesn't mean what I said is wrong.
    6) No.
    7) Get over yourself.
    8) Go read a real book on the subject.
    9) Learn how to carry on a civil discussion.
    *) What Wikipedia entry? It seems likely someone is going to have to go undo your damage.
    Last edited by MagiMaster; July 29th, 2011 at 11:24 AM. Reason: Typo
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  18. #17  
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    Phyz, members such as MagiMaster have earned the respect of the other posters on this forum by their willingness to help and also to learn from others.
    You've displayed neither of those two qualities yet. Work on it then get back to us.
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  19. #18  
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    Quote Originally Posted by peterpan View Post

    1), 2) that is the point ! what you detect in water is that there has happened a pair production
    That is only the effect,
    the causes can be many. A gamma ray hitting a nucleus produce the same effect.How can you affirm it was a neutrino?
    You're right that that is a concern. The way they screen for that is by placing the pool of water deep underground, where it's unlikely that any gamma rays would be able to reach it.

    3)thank you for your frankness. But do you really think they could annihilate?
    If they're true anti-particles with nonzero mass then they should be able to. However, nobody can even say for sure what their mass and energy is, so there's no way to predict exactly what kind of EM radiation they would emit if they did annihilate. In the earliest version of the theory of neutrinos, they were expected to have no rest mass at all. If that were true, then maybe they wouldn't annihilate. I don't know for sure.

    Neutrino - Wikipedia, the free encyclopedia - Mass section
    Some clocks are only right twice a day, but they are still right when they are right.
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