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Offline neilep

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What is a Neutrino ?
« on: 07/07/2005 18:02:59 »
I don't know if this has been dealt with before but can someone explain to me what a neutrino is and why they can only be detected in tanks of water a long long way underground ?...I also heard a story that astronauts were seeing flashes of lights when they closed their eyes ...was this caused by neutrinos ?..if not...what ?

cheers my dears !!



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Offline ukmicky

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Re: What is a Neutrino ?
« Reply #1 on: 07/07/2005 18:20:42 »
cosmic rays / Cerenkov radiation.
this link should awnser all your questions

http://www.ast.leeds.ac.uk/haverah/dets.shtml
http://www.cakes.mcmail.com/cerenkov/cerenkov.htm
« Last Edit: 07/07/2005 18:30:38 by ukmicky »
 

Offline neilep

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Re: What is a Neutrino ?
« Reply #2 on: 07/07/2005 19:55:46 »
Thanks for the links Michael...the second one is a bit heavy reading for little ole me !!..I was hoping for a laymans answer, one that you might find in 'John & Jane learn about Neutinos' or 'Sesame Street is brought to you today by the word Neutrino'...but thanks again...all very interesting stuff.

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Offline ukmicky

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Re: What is a Neutrino ?
« Reply #3 on: 07/07/2005 23:57:37 »
good thing i gave you the easy read link first , it tells you all you need to know

but i would of never of guessed that  you the man with your experience (3065 posts)
would find the second link hard to understand
« Last Edit: 08/07/2005 00:00:55 by ukmicky »
 

Offline neilep

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Re: What is a Neutrino ?
« Reply #4 on: 08/07/2005 00:30:07 »
quote:
Originally posted by ukmicky



but i would of never of guessed that  you the man with your experience (3065 posts)
would find the second link hard to understand



:D:DThanks Michael for the big grin you just gave me...i really needed it today !!..check my posts, you'll then see why I haven't a clue what the formulas/equations in your second link mean :D:D...put it this way !!..I do have a lot of experience...but only in posting on this site :D

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Offline gsmollin

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Re: What is a Neutrino ?
« Reply #5 on: 08/07/2005 05:43:00 »
quote:
Originally posted by neilep

Thanks for the links Michael...the second one is a bit heavy reading for little ole me !!..I was hoping for a laymans answer, one that you might find in 'John & Jane learn about Neutinos' or 'Sesame Street is brought to you today by the word Neutrino'...but thanks again...all very interesting stuff.

Men are the same as women.... just inside out !!



A neutrino is one of the elementary particles. It belongs to the family of leptons, and is associated with the electron. Neutrino means "little neutral one". It has no charge, spin 1/2, and no mass, or almost no mass. The neutrino takes part in the weak interactions and is part of radioactive decay. Actually, that was how it was postulated. When a neutron decays, it releases a proton and an electron. However, there was insufficient energy release in the decay, known as beta decay. A chargeless, massless particle was postulated to be carrying the energy away. That particle was the anti-neutrino. The reason it isn't the neutrino, is because the decay must conserve lepton number, and the electron has lepton number 1 and the neutrino has lepton number -1. Maybe this is getting beyond Sesame Street.

There are really three neutrinos, the electron neutrino, the muon neutrino, and the tau neutrino, each associated with its elementary particle.

The detectors contain tanks of fluids that contain elements that can interact weakly with the neutrino. If a neutrino hits the nucleus of one of these elements, and it has the correct energy, a reaction will occur via the weak interaction. The transmuted atom will release energy that can be detected. The detectors are miles undeground to shield them from cosmic rays that would add a lot of noise.

For years, there were problems with the neutrino detectors, and nobody was sure if the detectors were bad, or the sun wasn't producing enough neutrinos. Eventually, it was discovered that the neutinos could oscillate between types, known as flavours.

If you're still interested, there is a ton of literature on the web. here is just one link: http://www.pheno.info/hottopics/neutrinoshavemass/

« Last Edit: 08/07/2005 05:55:26 by gsmollin »
 

Offline neilep

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Re: What is a Neutrino ?
« Reply #6 on: 08/07/2005 13:38:23 »
Thank you Gsmollin and thanks again Ukmicky. I'm getting there...hoping to earn my white coat one of these days rather than be surrounded by people wearing them !!

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Offline Solvay_1927

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Re: What is a Neutrino ?
« Reply #7 on: 31/07/2005 00:20:24 »
I have a question about neutrinos.

I posted this on another physics discussion forum recently (before I'd discovered the far superior Naked Scientists forum, that is) but nobody there responded to it.  Maybe you people can help.  It goes as follows:

What happens when a neutrino and an anti-neutrino collide?

When a particle and its anti-particle collide, they annihilate each other and convert all their mass into energy (according to the formula E=mc2) in the form of photons.

But neutrinos and antineutrinos either have no mass (so Einsteinís formula doesnít help) or they have very very little mass.  But they do have energy (thatís why they were first postulated to exist, as an explanation for how some of the energy generated in radioactive B-decay gets carried away).  So what happens to this energy when they come into contact?  Is it converted into photons?  Do they just pass by each other?  Or is there some unknown mechanism that stops them from colliding?  (Or, more radically, does the distinction between matter and antimatter not apply to neutrinos?)

Being uncharged, I appreciate that they wonít be attracted to each other, but the sheer number of them passing through the Earth from all directions (from the sun, atmosphere, natural radioactivity in the ground, etc.) should allow some to come into contact, shouldnít it?
(Am I right in thinking that the combination of all these sources produces large numbers of BOTH antineutrinos AND neutrinos that are constantly passing through the Earth?)

If anyone has any bright ideas or can point me in the direction of some useful reference material (web links, books, etc.), Iíd be very grateful.

Thanks.
Solvay.

 

Offline gsmollin

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Re: What is a Neutrino ?
« Reply #8 on: 31/07/2005 03:23:53 »
A neutrino and an anti-neutrino can annihilate into an electron and a positron, under the right conditions. The last two references are the best.

Other researchers believe the neutrino is its own anti-particle. Since neutrinos are charge-less, that is quite possible. The only difference is their spins.

http://www.acadjournal.com/2001/v4/part4/p1/

http://hepwww.rl.ac.uk/OpenDays98/Century%20of%20electrons/quark2.html

http://hyperphysics.phy-astr.gsu.edu/hbase/particles/neutrino3.html#c1

http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005hep.ph....4052K&db_key=PRE&data_type=HTML&format=

http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1987A%26A...175..309B&db_key=AST&data_type=HTML&format=

Check out page 20: http://nanp.dubna.ru/docs/studenikin.pdf
here is a good one: http://citebase.eprints.org/cgi-bin/fulltext?
format=application/pdf&identifier=oai%3AarXiv.org%3Aastro-ph%2F0108196
« Last Edit: 31/07/2005 19:11:37 by gsmollin »
 

Offline Solvay_1927

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Re: What is a Neutrino ?
« Reply #9 on: 31/07/2005 13:58:47 »
Wow, you ARE a fountain of knowledge.

Many thanks gsmollin, these links look just like what I need.
 

Offline gsmollin

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Re: What is a Neutrino ?
« Reply #10 on: 31/07/2005 19:19:51 »
I'll try this one again. That last link was literally broken by me. Click on "cached .pdf" for the actual article. Seriously, guys, I don't know anything about this subject. Weak interactions are my "weakest" point in physics. The internet is the real fount of knowledge.

http://citebase.eprints.org/cgi-bin/citations?id=oai:arXiv.org:astro-ph/0108196
« Last Edit: 31/07/2005 19:20:37 by gsmollin »
 

Offline Solvay_1927

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Re: What is a Neutrino ?
« Reply #11 on: 06/09/2005 14:57:33 »
After a lengthy break, I've come back to considering this topic again, and something's just struck me.
(ouch)
A neutrino and anti-neutrino can annihilate to form a positron and an electron.
But photons also produce electrons and positrons.
So does this mean that photons can be considered to be made up of a combination (some sort of "resonance" or something) of a neutrino and an antineutrino?
Or am I just being really thick?
 

Offline David Sparkman

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Re: What is a Neutrino ?
« Reply #12 on: 06/09/2005 16:18:48 »
A neutron is composed of a proton and an electron as well as a binding force. So when a neutron decays which it can do naturally (they are about the lowest level radioactivity there is), or by collisions, they break down into these parts. An Anti-neutron would there for break down into a anti-proton and an anti-electron (Positron).

Each of these pairs can then combine with it's opposits to produe energy (read photons and anti-photons).

I believe there are pathways where energy can be shed from a photon that will produce matter, but that would introduce the idea that there can be an unbalanced force (more electrons then protons), which would be courious indeed.

David
« Last Edit: 06/09/2005 16:27:32 by David Sparkman »
 

Offline Ultima

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Re: What is a Neutrino ?
« Reply #13 on: 06/09/2005 18:13:43 »
An antiphoton is a photon.

wOw the world spins?
 

Offline Solvay_1927

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Re: What is a Neutrino ?
« Reply #14 on: 06/09/2005 21:31:29 »
David,
according to quantum electrodynamic theory, photons do indeed transform into electrons & positrons (spontaneously it seems) - but then of course the e+ and e- quickly annihilate each other again, so it's hard to detect.  But the balance is maintained in that a positron is produced for every electron (so there's conservation of charge) and a lepton for every anti-lepton.  As for the balance of protons and electrons in the universe, I don't see why that needs to be conserved (why should there be the same no. of leptons as hadrons?) - not that it matters in this case, as the imbalance doesn't last anyway (due to the rapid annihilation of the e+ and e- as I mentioned above).

Are we talking about the same thing, or are you saying that you've heard that photons can produce matter which isn't balanced by creation of an equal amount (and charge) of anti-matter?
 

Offline David Sparkman

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Re: What is a Neutrino ?
« Reply #15 on: 08/09/2005 03:21:39 »
Thanks for clearing that up.  I was reading up on quarks recently and found some curious ideas that Halons weigh more than their composite quarks due to the extra energy they have in them. Can you shead any light on those theories?

David
 

Offline gsmollin

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Re: What is a Neutrino ?
« Reply #16 on: 08/09/2005 17:04:37 »
quote:
Originally posted by Solvay_1927

After a lengthy break, I've come back to considering this topic again, and something's just struck me.
(ouch)
A neutrino and anti-neutrino can annihilate to form a positron and an electron.
But photons also produce electrons and positrons.
So does this mean that photons can be considered to be made up of a combination (some sort of "resonance" or something) of a neutrino and an antineutrino?
Or am I just being really thick?





The production of electron-positron pairs by neutrinos apparently can occur only near other matter, and under certain conditions. I don't see any relationship between this phenomenon and any concept that a photon is not an elementary particle. Particle-pair production occurs under many conditions throughout particle physics. As long as no conservation laws are broken, almost an unlimited number of particles can be formed fron energy available during energetic reactions.


"F = ma, E = mc^2, and you can't push a string."
« Last Edit: 08/09/2005 17:06:10 by gsmollin »
 

Offline gsmollin

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Re: What is a Neutrino ?
« Reply #17 on: 08/09/2005 17:13:25 »
quote:
Originally posted by David Sparkman

Thanks for clearing that up.  I was reading up on quarks recently and found some curious ideas that Halons weigh more than their composite quarks due to the extra energy they have in them. Can you shead any light on those theories?

David



I thought the opposite was true. The quark's mass is less when it is bound. A great deal of energy must be added to remove a quark from its hadron. In fact, since they are bound, at a certain point the energy added removing the quark exceeds its mass, and a quark-antiquark pair is formed. However, I can't remember the exact physics here, so this post is not too useful, except to confirm that a quark's isolated mass is very different from its mass inside of a proton, for instance.

"F = ma, E = mc^2, and you can't push a string."
 

Offline Atomic-S

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Re: What is a Neutrino ?
« Reply #18 on: 09/09/2005 04:26:45 »
In re. the production of electron-positron pair mentioned by someone above, that it takes place only near matter:

Converting an electron and positron into gamma rays by annihilation does not require the presence of additional particles. I understand that the mathematics of all this is reversible. If so, it should be possible, under certain circumstances, for 2 photons to come together and turn into an electron and positron speeding away from each other and not recombining. I don't think it has ever been observed, but theory seems to say it should be possible.
 

Offline Solvay_1927

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Re: What is a Neutrino ?
« Reply #19 on: 12/09/2005 13:22:36 »
gsmollin - thatnks for your answers above - you're a very useful guy to have around.  (Or is it gal?)

Maybe you - or someone - can help me with another query about neutrinos: What wavelengths are associated with neutrinos?

If neutrinos have mass (as per latest theory/experiments - see gsm's link earlier in this discussion), then can we use the de broglie equation to obtain their compton wavelength:
w=h/mc ?

And if they don't have mass, would it be possible/meaningful to treat neutrinos as if they were light, and use E=hf followed by w=c/f ?

In either case, what range of wavelengths would this give?

(P.S. Does anyone know how to insert greek letters - e.g. lamda - in these replies??)
« Last Edit: 12/09/2005 13:24:43 by Solvay_1927 »
 

Offline gsmollin

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Re: What is a Neutrino ?
« Reply #20 on: 14/09/2005 02:58:27 »
quote:
Originally posted by Atomic-S

In re. the production of electron-positron pair mentioned by someone above, that it takes place only near matter:

Converting an electron and positron into gamma rays by annihilation does not require the presence of additional particles. I understand that the mathematics of all this is reversible. If so, it should be possible, under certain circumstances, for 2 photons to come together and turn into an electron and positron speeding away from each other and not recombining. I don't think it has ever been observed, but theory seems to say it should be possible.



I have a cloud-chamber photograph of electron-positron pair production. A gamma ray photon enters at the top, passes through a lead shield and a e- and e+ exit at the bottom, curving in opposite directions from the magnetic field. It's a famous pic.

Two photons coming together does not normally result in a reaction. Since the photon is a boson, it can co-exist with another photon, i.e. two photons can pass through each other without colliding.

"F = ma, E = mc^2, and you can't push a string."
 

Offline gsmollin

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Re: What is a Neutrino ?
« Reply #21 on: 14/09/2005 03:05:32 »
quote:
Originally posted by Solvay_1927

gsmollin - thatnks for your answers above - you're a very useful guy to have around.  (Or is it gal?)

Maybe you - or someone - can help me with another query about neutrinos: What wavelengths are associated with neutrinos?

If neutrinos have mass (as per latest theory/experiments - see gsm's link earlier in this discussion), then can we use the de broglie equation to obtain their compton wavelength:
w=h/mc ?


And if they don't have mass, would it be possible/meaningful to treat neutrinos as if they were light, and use E=hf followed by w=c/f ?

In either case, what range of wavelengths would this give?

(P.S. Does anyone know how to insert greek letters - e.g. lamda - in these replies??)




I'm a guy. I don't give out too much info on the internet, but I will volunteer that I'm a regular guy.

The wavelength question; I would have to search around for ranges of energy and mass before I could venture a number. I suppose its safe to say there would be a matter wave. The mass of the neutrino is still pretty preliminary.

"F = ma, E = mc^2, and you can't push a string."
 

Offline Atomic-S

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Re: What is a Neutrino ?
« Reply #22 on: 18/09/2005 05:31:23 »
The wavelength of the neutrino ought to be a fairly straightforward problem: For any quantum particle, w = h/p  p being the momentum. In the case of massless light, the momentum energy relation is obtained very straightforwardly -- I believe it is simply p = (cp)^2/2E . so we end up with w = 2hE/(cp)^2 . The same formula should work for a neutrino as well, very nearly, under the assumption it is moving at or near the speed of light, which is ordinarily the case. Now in a reaction creating a neutrino, such as radioactive decay, I seem to recall that in one typical case, the neutrino is emitted in conjunction with an electron, the two particles sharing momentum on sort of a continuum from zero up to the maximum, which I think is the same for both. According to that, the wavelengths should occur over a range from h/0 through h/(max momentum of electron), meaning that the neutrino wavelenghs would cover the same range of wavelengths that the electrons wavelengths would. Which are generally quite short. (We have here, incidentlaly, the curious result that two particles moving at widely different speeds but having the same momenta, will have the same wavelength.)
 

Offline Atomic-S

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Re: What is a Neutrino ?
« Reply #23 on: 18/09/2005 05:47:25 »
quote:
Two photons coming together does not normally result in a reaction. Since the photon is a boson, it can co-exist with another photon, i.e. two photons can pass through each other without colliding.


In classical electrodynamics that would be called, I believe, "superposition" or linearity. Still we are presented with the difficulty that the annihilation of a positron and electron to become photons does not seem to be reconcilable with the concept of electromagnetic linearity, so one comes away with the sense that the electromagnetic field cannot be strictly linear. We could probably say this another way by saying that although 2 photons can and usually do pass through one another, they need not do so in every situation. Of course, in order for pair production to occur from photons alone, there must be enough energy to do the job. That is going to require at least one of the photons to possess a very short wavelength. Actually it will require more than that:  Viewed relativistically, what reference frame would we view the process in? Both photons are moving at the spped of light in whatever frame we choose, and we can assume that if, in a given frame, there is insufficient photon energy to produce the pair, then the pair will not be produced in any frame. (The fact of production or non-production is the same for all possible observers). But since we can always find a frame in which at least one of the photons has enough energy for pair production, having such energy is necessary but cannot be sufficient. So there must be some other requirement also. Well, obviously, an extension of this requirement must be, since pair production if it occurs takes place in all frames, that there be enough photon energy present regardless of the frame. I believe that this requirement dictates that the situation be somewhat like the following:  The photons must be travelling in opposite directions and together must possess the necessary energy. Maybe this can be simplified down to say that it is necessary that in the frame in which the photons are travelling in opposite directions and have equal energy, the energy of each must equal the mass equivalent of an electron or positron. (This also tells us how to select the reference frame for analysis). If we cannot find such a frame, then pair production is impossible. If we can, pair production pair production is possible in principle, but the question arises as to its probability. Of course this might have something to do with how many photons are present, and their spatial concentration. But still the assertion is made, that given such conditions, pair production from photons, with no other particles explicitly present, should be possible.
 

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Re: What is a Neutrino ?
« Reply #23 on: 18/09/2005 05:47:25 »

 

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