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Science

Underwater telescope to study neutrinos 117

Posted by Hemos from the to-study-space-go-underwater dept.
Darksky wrote to us with information about the proposed 'Antares' telescope. The proposal would be to put a telescope 2.4 kilometers underwater, in an attempt to study neutroino/cosmic rays. The telescope would use the the Earth as shield from cosmic rays, and hopefully study the muons liberated by the neutrinos.
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Underwater telescope to study neutrinos More

Underwater telescope to study neutrinos

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  • Yeah, the cat throws them there. (Score:1)

    by Anonymous Coward

    It's a pain in the ass, I'm telling you.

  • Re:Hmmmm..... (Score:3)

    by Faramir ( 61801 ) on Tuesday September 14, 1999 @06:25AM (#1682885) Homepage Journal

    We can produce massive amounts of neutrinos. But it also takes massive amounts of work. I work on a project called MINOS--Main Injector Neutrino Oscillation Search. We will be shooting a beam of neutrinos (mainly muon type) from Fermilab outside of Chicago to northern Minnesota. At each end, we will look at the flux of each type of neutrino and compare the ratio of types. If the ratio is significantly different than 1, but the overall number of neutrino ratio between detectors is around 1, then this will indicate that neutrinos do indeed have mass. Cool project, but a little beside the point.

    Anyway, I've been touring the facilities the last few days, and I can tell you that the accelerator beamline is over 1 mile long, just to reach northern Minnesota. The two detectors, one on each side, will require abou 2,700 tons of steel each (no exaggeration!). So while a neutrino antenna may be able to use different (lower) energies than we are using, I can't imagine that the required equipment would be much different than this. More information can be found at U of Minnesota [umn.edu].

  • Right, I assume that's what's meant by "if you can produce and detect neutrinos." On top of the concern you've written, there's also the problem that there's an enormous background of neutrinos whizzing around from stars, supernovae, and the matter-antimatter annihilation after the big bang.
    Separating your signal from this noise would be difficult, I would think, even if you could detect neutrinos readily.
  • Don't be picky about spelling, lest I respond like this: (alterations in boldface)

    • Hey
    • , we {really|actually|probably|...} should be looking for gravitons. They would have useful and practical value in society. Imagine {such things as|having|having such things as} graviton space engines, graviton suspensor fields, and the like... yum! But anyway...

      Hemos, it's "neutrino." Man, you need a spelling checker.... ;)

    Sorry to be picky, but using .... where ... should be, and vice-versa, and having missing commas, and using "its" instead of "it's," and incorrectly quoting your punctuation, and having atrocious sentence syntax, and then having the gall to point out one insignifigant typo is just a bit asinine.
    ---
    "'Is not a quine' is not a quine" is a quine.
  • I was under the impression that it's still an open question whether neutrino oscillations occur.
  • Like what if it's Schrödinger's cat? As far as you know the barfed up gravitons are both there and not there...

  • Yes, the Sudbury Neutrino Observatory is located
    in an old mine in Northern Ontario. Check out:
    http://www.sno.phy.queensu.ca/

  • AMANDA (Score:1)

    by Anonymous Coward
    some novel idea. http://amanda.berkeley.edu http://www.pico.unl.edu amanda has been around for a few years.. not as easy as dropping a few pmt's - photo multiplier tubes overboard and pointing them at the ocean floor..
  • Maybe I'm missing something but since we don't know where cosmic rays come from (according to the article), and since the earth's mass is only blocking half of the spatial sphere around the Antares, isn't there going to be some kind of problem with cosmic rays coming from the half of the spatial sphere around the Antares that isn't blocked by earth's bulk?

  • BTW, that was a joke, hence the wink in ";P".
    --
  • I don't know what became of DUMAND; it may have fallen prey to Congress in a budget cycle, because it was too small to have a constituency to defend it. Kind of like NASA's science programs.

    I'm working in one of the labs that collobrated for DUMAND and I believe that it died due to budget cuts. Some of the detector strings are being used in NESTOR in Greece though.
  • You sort of got the lead part backwards :) Lead stops gammas perfectly well. You have to be careful when using lead to shield betas, because you get bremstrahllung (sp?) X-rays. Compact neutron shielding is the hardest one. You first have to thermalize any fast neutrons (with water or some kind of plastic with lots of hydrogen, for the reasons you described), then surround that with a neutron absorber (e.g. boron or cadmium), but _that_ produces gammas (and alphas also in the case of boron), which have to further be shielded by, e.g. lead.

    But they're looking at neutrinos, not neutrons anyway.
  • Yes, but the whole point in going undersea is the vast size of the site. The mines in the mountains are rather limited in size and access - and still they dont shield well enough and produce too many false hits/events. Undersea you can install an arbitrary number of detectors, and the shielding is perfect.

    The problem with undersea detectors is that you can't control the water quality as well as in a tank. Also there is a limitation on the effective size of the tank due to the attenuation of the cherenkov radiation by water. Pure 18megaohm water has an attenuation length of about 300 meters(the intensity drops by ~67% after 300m) so the volume you're sampling is limited by the number and location of the detectors. True you can add more detectors but there are pratical problems with that.

    The shielding in the mines are pretty good considering its about 1500m underground so you have about 1500m of earth and rock shielding you. However the ocean detectors can have more shielding if it's placed at a sufficient depth.

  • Okay, what are the side effects of being exposed to a constant bombardment of this type of energy, could this be lethal? Will the bird building its nest on the detectors be fried? I don't know enough about dangerous forms of energy, but the xray post about communications made me think about using these things for communication, hence the thought of danger, if I recall correctly x-rays aren't the best to have shot on you ;)
  • Sure. But given that they largely pass through ANYTHING due to their small size, or whatever, how do you plan to receive the transmission?
  • Not quite - E=mc^2 is only true in the rest frame of the particle. That is to say, if you see an electron flying past at speed v, and you speed up until you're travelling at the same velocity as it is, then you will measure it to have energy E.

    The more general form of that equation is E^2 = p^2c^2 + m^2c^4, where p is the momentum and c is the speed of light (299792458 metres per second).

    If you see an electron flying past with momentum p, you can speed up until you're travelling with the same velocity, at which point it will look (to you) as if it has no momentum, p=0. Then you will measure it to have energy E=mc^2. Now, if neutrinos had zero mass (it looks like it's close to, but not quite, zero), they would travel at the speed of light - in which case you could *never* speed up until you were travelling with the same velocity, since you have mass and therefore can't get to light speed. Hence, if you measure the energy of a neutrino, it will always come mostly from the momentum, not the mass. In fact, this is true for any particles travelling fast enough (the physics jargon term for "fast enough" is "highly relativistic" - meaning that the speed is so high that Newtonian ideas go out the window).

    If you're interested, find a decent text on relativity:- the relevant chapters of Halliday, Resnick and Walker, "Fundamentals of physics" are quite good at explaining the basics without needing anything more than high-school maths.

  • The rate of interaction (cross-section) between normal mater and neutrinos is vanishingly small. However, if you make a lot of them, it begins to be a problem. But if peoples guesses have any meaning, we would need several orders of magnitude more of them for them to start doing the kind of damage cosmic rays do.

  • It was a simple question dumbass..I thought I had read, somewhere, that they had used an old mine because of the shielding it provided. I'm was inquiring if anyone knew anything further. That's all. Sooorryy, I guess I'm not as worldly as yourself.

  • Yes there have been quite a few underground neutrino detectors over the last ten years or so. However all of them keep returning anomalous results. They were intended to measure the level of neutrinos streaming out of the sun from fusion reactions. However, the measurement from the detectors has uniformly been below the predicted level of neutrinos by a factor of three. Originally it was merely thought to be an error in measurement or faulty detectors. But as more facilities and more sensitive detectors were built, the measurement of 1/3 of the neutrinos that calculations predict has gotten increasingly solid.

    Perhaps this one will finally shed some light on the 'puzzle'. :)
  • his might be the same project that I read several years ago in Discovery magazine. It basically was going to use neutrinos to map the center of the earth. The detector looks for the light discharge when a neutrino actually interacts with an atom, creating a muon. And based on that, it was supposed to image the center of the earth, because they would know the velocity and the direction. Since neutrinos are nearly weightless, they are noncharged, and they are very small, they would just pass right through the earth.
    The current models of the Sun indicate great quanities of neutrinos should be produced, but observation has said otherwise. This project might be able to figure out where the lost neutrinos have gone.

    anyway, the ramblings from an ex-particle physics geek.
    --
    Gonzo Granzeau

  • actually, someone has already hung a network of photomultipliers off of Hawaii to do the same thing.

    As far as the people who put big tanks of stuff with photomultipliers in them, they usually use dry-cleaning fluid in them, not H20. They have the PM tubes to detect the flashes, but actually count the amount of argon gas "cooked" off by the neutrino collisions for the aggregate rate.
  • Oh, but there _must_ be, if current quantum theory is correct.

    Each force has an associated particle that carries it. Too bad I can only remeber that photons carry electomagnetic, and gravitons are _supposed_ to carry gravity.

    Of course, the theory could be wrong...
  • making neutrinos will be much easier than detecting them.

    Check out the capture rate of the neutrino detectors... it's pretty sad.
  • It's much more likely that my cat ate them and them threw them up on the kitchen counter. He likes to do that.
  • I was under the impression that it's still an open question whether neutrino oscillations occur.

    The SuperK experiment did detect the neutrino oscillations so the fact that it happens is somewhat well established. The findings also provide strong evidence for the existence of neutrino mass since other explanations have been eliminated.
  • I thought it was interesting because scientists theorize that the "missing" mass associated with current models of the universe could possibly be accounted for in the neutrinos - if it turns out the neutrinos actually have mass.

    SuperK has provided good experimental evidence for the existence of neutrino mass. However, whether this accounts for the missing mass or not is still up to debate.
  • I'd be happy to answer.... NO JOKE!! We humans do not enjoy a level of technology to directly observe gravity. Newton can watch, and feel the apple hit his head. But Newton could never, and we can never look at gravity in a microscope. WE cann't touch gravity, weigh gravity, or look at gravity. Have you ever seen gravity?? Scientist get around this problem by observing the effects of gravity on its environment. The apple falling, or the stars expanding away, or the turning of a spiral galaxie. One of the things the Super conducting super collider would have given us humans is the advanded way of observing an ever smaller arena of sub atomic particles. The people responsible for thinking up those type of devices decided that they would make a particle accelerator big enough to send two nutrinos in opposite directions at the speed of light, and actually force them to collide on a closed loop, and then (hopefully) observe very small particles breakdown into smaller particles. The Big thinkers are trying to show the existence of particles like gravitons, but that won't happen in an underwater observatory type deal. IT might take several hundred years to get that one chance collision. AND at that, they might not find what they think they will find.
  • This is somewhat off-topic, but neutrinos have long been a staple of science fiction plots. Examples:
    • Larry Niven's "deep radar".
    • The scanning technology used to detect the first "bobbles" in The Peace War (Vernor Vinge).
    I also recall a relatively recent short story in Analog which got the hazards of being close to (as in, on a planet around) a supernova right: unless you have a neutrino shield, the number of neutrino-collision events in your body will kill you almost instantly from radiation effects. Dumping a solar mass of high-energy neutrinos overwhelms the tiny odds of any one of them deigning to notice that your atoms exist.
  • In this example, gravity is a force of nature that is thought of in two ways: Strong nuclear force, and Weak nuclear force. These two forces combine to be what we call gravity.

    The strong nuclear and weak nuclear force are different from gravitational forces. The strong nuclear force is mediated by gluons or mesons depending on whether it is affecting quarks or hadrons. The weak nuclear force is mediated by W-,W+, and Z0 bosons. The two forces do not combine to form gravity. Gravitons are postulated to mediate gravitational attractions but has not been detected yet.

    It is a rare event to actually stop a nutrino, and the chances are slim that you can force it to happen in a lab. So some smart scientist decided one day to use an old abandoned mine under mount fuji in Japan. There is several giga-tons of mountain for nutrinos to go thru untill the poor particle finds itself in a big nutrino trap. hehehehe The equipment is so sensitive that nothing must ever move in its presence, and people are advised to not go near them.

    That is totally untrue. I know for a fact that SuperK is located in Toyama near Mizumi. Also its in a aluminum mine. Last I heard Mt. Fuji wasn't being mined. Also the equipment is not that sensitive. People routinely go to the top of the tank to adjust stuff. In addition, the mining company is doing some blasting a couple hundred meters away the control center and tank and this is not affecting the instruments.
  • That about wraps it up. I haven't had time to check out the details of this proposal. I'll be interested to see how they plan to get the water sufficiently clear that they can detect the scintillations from the muons. If the water is too murky, then the tiny Cherenkov flashes get absorbed, and you don't get any signal. Perhaps the sea water clears up if you go down deep enough?

    It's surprising but some locations in the ocean have water clear enough that the attenuation length is about 200m. For example, the DUMAND site off Hawai'i had water that was about that clear. For comparision 18megaohm (100% pure) water has an attenuation length of about 300m so its not that bad.
  • How are they going to filter out the light produced by bioluminescent marine organisms? I thought they were common in the deep ocean.

    I believe that the bioluminesence occurs at a wavelength quite different from the cherenkov radiation that the neutrino interactions produce. The neutrino interactions produce radiation at about ~400-500 nm which is right at or above the upper edge of human vision. So you can probably filter out bioluminescence by constructing the appropriate filter or ignoring lower energy photons.
  • I'm not sure about the number of Bs and Ps, but it definitely starts with a K. I've seen it as Krabaple, Krabbaple, Krabapple, and Krabbapple. Whatever. :)

    As for the person who seems so deeply offended that he was so deeply offending regarding spelling: Get over it.
    ---
    "'Is not a quine' is not a quine" is a quine.

  • Gravitons do exist, even if only as a theoretical construct in the realm of quantum gravity, which is the attempt to unify the theory of relativity with quantum mechanics, by trying to explain the behaviour of the universe at planck lenghts (1 x 10 to the -35th power).

    A mechanism called perturbative quantum field theory has been successfully used to express and explain electrodynamics. Perturbative quantum field theory is essentially the sum of many method, summing all (or as many as possible) potential pathways which are renormalized after the subtraction of infinities from the corresponding Feynman diagrams. In the realm of quantum gravity, this same approach is being used by some physicists, and one of the theoretical constructs used to aid in this expression are gravitons, described as zero order approximations to quantized gravitational waves in flat space-time. There are already a set of expected characteristics of these particles, such that they are spin two massless particles.

    It might not be immediately obvious what, if any, connection a neutrino observatory could have in regard to gravitons, but I would argue that the attempt to understand both the sources and behaviours of neutrinos, especially at high energies, would translate to a potential ability to examine events at the planck length, which to do so in an accelerator would require an accelerator 10 to the 15th times more powerful than any currently existing.

  • I generally have a more open mind towards people who understand simple spherical trigonometry. We on Super-K use cos-theta to keep equal solid angle bins, and these jokers think it's because we're hiding something. Whee.
  • Actually, the studies of the Sun's vibrations ("helioseismology") have done a really good job of confirming that the sun is indeed put together the way astrophysicists have always claimed. Thus, the sun is indeed fusing properly.

    This evidence supports the proposals that the deficit of observed neutrinos from the sun has to do with something weird happening to the neutrinos themselves rather than something weird happening to the sun.

  • Antares (and the other big under sea/ice neutrino telescopes) have a pretty high energy threshold. They can only see neutrinos which are thousands of times more energetic than those produced by nuclear reactions (like in the sun). Also, these experiments are most sensitive to muon-type neutrinos, and those produced by the sun are electron-type. So, they won't provide much information at all on the solar neutrino puzzle.

    The area where the big undersea detectors are hoping to contribute is as neutrino telescopes looking for possible high-energy astrophysical sources of neutrinos, like the supermassive black holes at the centers of many galaxies. These produce large, highly energetic jets of material as they suck in stars and stuff. One side effect of this is that very energetic muon-type neutrinos are also produced. If Antares et al can observe these neutrinos, it will be a great probe of what's going on in the centers of these interesting galaxies.

  • I'm saying that the neutrino background is a lot higher than the radio background, because radio waves are easily absorbed, and because there's an enormous neutrino background from the epoch of matter-antimatter recombination. The closest parallel to that in the radio is the cosmic microwave background, which has a much smaller energy density and is not in a band we use for communication. I think you have no sense whatsoever of the differences involved. Just because there are natural sources for both doesn't mean that they are equal in magnitude.
  • The probability of detecting any one nuetrino is incredibly small. But the physics works out pretty well with our beam size going into 2700 tons of steel.
  • I don't have any numbers on me, but we are already being bombarded by tons of neutrinos. The things are so penetrating that they can go right through the earth and keep going through you and back into space. Naturally, there will be no bird nests on the detector (or anything else). In fact, the primary detector in Minnesota will be about 2/3 mile below ground. Thankfully, there is a substantial difference between photons and neutrinos: photons interact very strongly with electrons, and neutrinos barely interact with matter at all. And xrays are, of course, a type of photon. No, its not good to have xrays shot at you, because they tend to excite electrons, which effect can then cascade into all kinds of things, including genetic mutation-->cancer.
  • that the answer to space mysteries would be at the center of our earth? :)

    havnet they tired this before? maybe not a telescope at the middleof the earth, but a big tank of pure H20, lite hydrogen(1 proton, no neutron) some where at the bottom of a long series of tunnels under the earth?

    hoping for somethign new...its an idea...

    Gorfin

  • Oh... so that's what happened to Captain Nemo. Seriously though, that's a decent engineering accomplishment. Working under that much water could be considered more difficult than working in space.
  • Joe Haldeman came up with this one, in a book called The Forever War. Basically, if you can produce and detect neutrinos, then you can use neutrinos as we currently use radio-spectrum photons. Specifically, you have something like a radio where everything is line of sight.

    So much for the comm satellite market...

  • Hey we should be looking for gravitons. They would have useful and prictical value in society. Imagine graviton space engines, graviton suspensor fields...yum. Anyways....

    The proposal would be to put a telescope 2.4 kilometers underwater, in an attempt to study neutroino/cosmic rays.

    Hemos its 'neutrino'. Man, you need a spell checker... ;)
    --
  • /me rushes to Foresight Exchange [ideosphere.com] to check the ticker for activity on claim Neut....
  • Will it be able to peak into womens bedrooms???

  • Some further info on ANTARES (Score:3)

    by Aleatoric ( 10021 ) on Tuesday September 14, 1999 @03:49AM (#1682943)
    Here are a couple of links to the antares site, with some more in depth information about the project.

    http://antares.in2p3.fr/antares/antares.html
    http://antares.in2p3.fr/antares/booklet/english/ intro_texte.html

    Here's a site with links to most of the other research involving neutrinos.

    http://www.phys.washington.edu/~superk/links.htm l

  • Heh, look who's talking....

    prictical=practical
    --

  • SNO (Score:3)

    by Tekmage ( 17375 ) on Tuesday September 14, 1999 @03:50AM (#1682945) Homepage
    The Sudbury Neutrino Observatory [queensu.ca] is a similar project - a sphere of heavy-water buried 2km underground.
  • Actually, they have tried this same type of experiment in different forms. Of the two that I can remember, one occured in a special lab in the middle of a mountain in the Alps and the other occured in Japan. They have large numbers of large photodetectors along the walls of the tank which is filled with a liquid (usually a (heavy) water but I heard that one used clear detergent). It was experiments like this that actually proved that neutrinos exist.
  • Yes, but the whole point in going undersea is the vast size of the site. The mines in the mountains are rather limited in size and access - and still they dont shield well enough and produce too many false hits/events. Undersea you can install an arbitrary number of detectors, and the shielding is perfect.
  • There's only one problem with looking for gravitons: there ain't no such animal.

  • Nonsense. (Score:2)

    by Anonymous Coward

    . . . and hopefully study the morons liberated by the nutrinos.

    You can't liberate morons, by nutrition or any other means. They have to liberate themselves.

  • They're just about (or should have already) finished some very impressive large neutrino detectors near the South Pole. A frozen lake where the water is very very pure punctured by kilometre (longer, even, but my memory is sketchy), and detectors lowered into them. Was fascinating.

    This is too, but on a different level.

    --

  • One of these experiments did occur in the US with vast tanks of D20 (heavy water). There was a special on 'NOVA' for those of you that like to watch PBS.
    I don't recall the specifics but there was an agent in the D20 that when hit by a neutrino created a Chlorine molecule I believe (Cl2) and they tried to measure the amount of gas released/formed. I think I watched this sometime between '90 and '92. So yeah, its been awhile.

    -Vel
  • If it's possible to build something to produce neutrinos on a mass-scale and release them under controlled circumstances.. we could communicate unidirectionally to any location on the planet - imagine how fast the internet would be if every computer had a 100mb connection to any point on the globe. Amongst other uses....



    --

  • Hey now... Work in Cambridge... Live in Arlington... To be fair, the sphere is a *little* bigger than that =)

    ---
    Joseph Foley
    InCert Software Corp.

  • Re:who woulda thunk... (Score:5)

    by mph ( 7675 ) <mph@freebsd.org> on Tuesday September 14, 1999 @03:58AM (#1682954)
    The first solar neutrino detector was at the Homestake gold mine in Lead, South Dakota. It used perchloroethylene, a cleaning fluid, to provide chlorine which would be converted to argon in a reaction with neutrinos. You have to count the argon atoms periodically, so you don't get immediate notification of an event, nor good time resolution.

    Mont Blanc uses a liquid scintillator, which emits a flash when a neutrino event occurs. This approach has the advantage of providing immediate notification and good time resolution.

    The detector with the coolest name is Super Kamiokande, in Japan. It was originally designed to detect proton decay by observing the Cerenkov radiation from the fast electrons that would be a decay product, but it also can detect neutrinos. It also provides immediate notification and good time resolution.

    The most famous result from neutrino detectors is that the observations of the solar neutrino emission do not agree well with theoretical predictions.

    In addition to the detection of solar neutrinos, neutrino detectors also scored big-time by detecting the neutrino burst of supernova 1987a. Because neutrinos pass through just about anything, these observations were useful probes of what was happening at the center of the SN.

    Notes for a talk I gave in an undergrad class are available at http://wopr.caltech.edu/~mph/papers /neutrino.ps [caltech.edu]. References to other works are included.

  • Yea, most have never been there. I appreciate what you are saying.

  • There was an article in Scientific American about detecting neutrinos/etc. a couple issues back.

  • Also, there is another neutrino observer planned somewhere in Canada that I stumbled across surfing the Web. "Snow" something I think it is called.

    I thought it was interesting because scientists theorize that the "missing" mass associated with current models of the universe could possibly be accounted for in the neutrinos - if it turns out the neutrinos actually have mass.

    I don't recall if there have been any conclusive observations made with relation to neutrinos and mass, but it seems at least that several different types of neutrinos have been identified.
  • How are they going to filter out the light produced by bioluminescent marine organisms? I thought they were common in the deep ocean.
  • Probably put itside something that blocks
    outside light.

    That's what I would do.
  • It's surprising but some locations in the ocean have water clear enough that the attenuation length is about 200m. For example, the DUMAND site off Hawai'i had water that was about that clear. For comparision 18megaohm (100% pure) water has an attenuation length of about 300m so its not that bad.

    200m seems a stretch. The clearest SK has been is 80m - 100m, depending on how you measure it. I can't imagine ocean water being clearer than SK water. If you are correct, then it is indeed surprising.

    BTW, who are you?

  • Ah geez, a joyce freak. Didn't we spray for those last week? Oh well, time to call the exterminator again...
    --
    "HORSE."
  • I could be wrong, but I think this project has everything to do with neutrinos and nothing to do with neutrons (pretty big difference)... although you are right about having to shield the detector... since neutrinos routinely fly right through the planet (and trillions through every square inch of you) every day it is a rare occurence that one gets stopped and detected. Hence the use of giant spheres of heavy water buried deep in the ground.
  • It was experiments like this that actually proved that neutrinos exist.

    That's only true for very large values of prove. If you believe in conservation of momentum, you just need to look at the beta decay of a random nucleus near you and notice that the two bits you can find afterwards (the nucleus and an electron) aren't going in opposite directions. This means the nucleus must have spat out something else to conserve momentum.

    Because you can't find the missing bit (i.e. it doesn't interact with any of your detectors) you strongly suspect it's neutral. By measuring the bits you can see and doing some arithmetic, you can find out its energy and momentum, and then some basic relativity tells you that it has very little mass and is travelling close to the speed of light.

    Hence you might decide to call the missing particle a little neutral thing, but since an Italian found it first, it's known as a neutrino. So in fact neutrinos were first discovered by analysing their production, not their absorption.

  • The Neutron flux at the earth's surface is pretty small. I doubt very much that it would produce an appreciable background. Certainly, I've never heard anyone talk about it at any neutrino detector talk I've ever been to. The Super-Kamiokande info [uci.edu] page, for instance comments:

    The detector is located deep underground in order to shield it from cosmic ray muons by the rock above it.

    -r
  • I read somewhere that not only was neutrino flux low, but the vibrational frequency of the sun was wrong.

    The sun, as everyone knows, is fluid -- it's generally considered to have a solid core, though. Because it's fluid, it oscillates somewhat, and that oscillation can be measured. The problem, according to this article, is that the period of the oscillations is wrong for a solid core -- OTOH, it's almost perfect for a constant-density fluid sphere. The first and second harmonics also match this model (I haven't seen anything about the third harmonics, presumably they don't match or are too small to measure).

    This adds up to a possible explanation for the lack of neutrinos: the sun isn't fusing. This is also supported by the shrinkage we've measured and deduced.

    The energy output we recieve would then be provided mainly by gravitational collapse.

    I don't know what this will do to the future life of the sun -- possibly reduce it to millions of years rather than billions. Presumably our theories of stellar lifecycles need a little adjusting.

    I wonder when the sun flamed out? And will it start up again?

    Oh, BTW, the study which originally reported the discrepency was russian; it was repeated with new data in the UK. I don't remember anything else about it.

    -Billy
  • if it turns out the neutrinos actually have mass.


    hmm, if E=mc2, and they are moving (thus energy in some form or another, to lose to the muons) wouldn't they have to posess mass? If not, could somebody explain why?
  • Uh, thanks alot Mrs. Krobopal! If you didn't notice, he always misspells words and I was only a joke, hence the ";)". Go back to grading your test papers... ;P ...having the gall to point out one insignifigant typo is just a bit asinine.

    "Insignificant" is the work I think you meant. :P
    --
  • That's a fine idea, but collision detection would be a bitch. ;-)
  • The amount of energy that you would need to produce enough neutrinos to detect your signal with normal matter makes this impossible.

    You'd probably be better off firing x-rays through the earth and trying to detect them that way.

  • A previous idea to do just this, the DUMAND (Deep Underwater Muon And Neutrino Detector) was originally proposed to be put in some very clear water which lies off the coast of Hawaii (IIRC). The detectors would have consisted of long strings of glass buoys anchored to the ocean floor, with very sensitive photodetectors to catch the faint flashes of Cerenkov radiation from newly-created muons racing through the water.

    I don't know what became of DUMAND; it may have fallen prey to Congress in a budget cycle, because it was too small to have a constituency to defend it. Kind of like NASA's science programs. <sigh>

  • No one knows that. You may be surprised someday...
    --

  • Hmm... (Score:3)

    by Enoch Root ( 57473 ) on Tuesday September 14, 1999 @04:10AM (#1682979)
    That's quite clever, for a number of reasons:

    The reason why water is used in radiation shielding is that it contains two Hydrogen atoms per water molecule. Since an atom of Hydrogen has more or less the same mass than a neutron, it acts like a billiard ball: the neutron tends to stop, and the proton is transferred all the kinetic energy. And since the proton is a charged particle, it stops quickly.

    Anyway; that means it's good shielding against neutrons. You still have neutrons coming from the environment ("thermal neutrons"), and if the telescope is exposed directly to water, this solves the problem. But you don't need to put it so far down underwater.

    Finally, gamma radiation: that's photons. how do you stop these? With difficulty, most of the times. Lead does it, but then lead also emits thermal neutrons! So you have to choose a way to stop both, which you can't.

    Except that at this depth, most of the gamma radiation coming from the Sun is absorbed already.

    It's a bit of an anti-Hubble: Hubble needs to be in space to be exposed to as much "noise" as possible, whereas this telescope needs to be shielded from almost everything.

    "There is no surer way to ruin a good discussion than to contaminate it with the facts."

  • Does not Canada have an advance research lab, located in an old mine, in Northern Ontario, which studies this very phenomenom?

  • they could dig a small hole for the receptor to look into.
  • You have the wrong physics here; this project is looking for neutrinos, not neutrons. The deal with neutrinos is that they seldom interact with other particles, which makes detecting them problematic, since ultimately we detect particles through their interactions with the particles that make up our detectors. However, "seldom" is not the same as "never". There is a constant stream of neutrinos passing through the earth, and even though only a tiny fraction of them interact, the result is a measurable number of detectable events per day.


    The key here is that the bigger your detector, the more collecting volume you have; thus, the more events you see. Traditional detectors have used huge tanks of water, cleaning fluid (CCl_4), or Gallium to get the necessary volume, but there's a limit to how big you can make the tanks. The beauty of using the ocean (or the Antarctic ice pack for another proposed experiment) is that the "tank" is already built for you.


    Now, there's another problem, and that is that when a neutrino interacts you still don't see the neutrino; you see the byproducts of that interaction. In this sort of experiment that would be a muon, a particle similar to (but much heavier than) an electron. The problem is that cosmic rays are filled with muons. If you want to see the muons produced by neutrino interactions you need to screen out all that background. Fortunately, muons are easily screened; just put a bunch of junk between you and them. That's why traditional neutrino experiments are located in tunnels or mines. Here again, by using the ocean you win because if you go deep enough you already have a lot of stuff between you and the cosmic ray muons.


    That about wraps it up. I haven't had time to check out the details of this proposal. I'll be interested to see how they plan to get the water sufficiently clear that they can detect the scintillations from the muons. If the water is too murky, then the tiny Cherenkov flashes get absorbed, and you don't get any signal. Perhaps the sea water clears up if you go down deep enough?


    -r

  • If only it worked that way. The figure I've seen is that a neutrino can go through a trillion miles of lead without interacting with anything, so your chances of detecting an individual neutrino are vanishingly small. Unless you can generate enormous quantities (with enormous energy requirements), you won't get enough of a signal at your detector to be able to communicate. Fortunately for Comsat, their technology is unlikely to be supplanted by neutrino systems any time soon.
  • You misread my post. The point is to shield the detector from neutrons, so that only neutrinos reach the detector. Since they're both of neutral charge, they affect the detector in the same way. So if you don't take out the neutrons, it's akin to trying to find a ball the size of a pinhead in a room filled with bowling balls.

    "There is no surer way to ruin a good discussion than to contaminate it with the facts."

  • Pay attention, darnit... The point is to shield yourself from neutrons, so only neutrinos come through. Of course I don't think this is a neutron observatory.

    "There is no surer way to ruin a good discussion than to contaminate it with the facts."

  • The reason why water is used in radiation shielding is that it contains two Hydrogen atoms per water molecule. Since an atom of Hydrogen has
    more or less the same mass than a neutron, it acts like a billiard ball: the neutron tends to stop, and the proton is transferred all the kinetic
    energy. And since the proton is a charged particle, it stops quickly.

    often these neutrino telescopes use "heavy water" -- that is water formed out of hydrogen with two neutrons, so that it absorbs even more background radiation...

    it's suprising these things can even pick up anything as well shielded as they are.
  • Bear with me here a sec... it has been a few years since any of my Nuke Eng classes.

    Now yes, you do get neutrons from the environment. But very very few. Neutron decay is not a common mode of decay for most isotopes. You tend to get more alpha, beta, and gamma decays. A 'thermal' neutron is a neutron who's velocity is predominately determined by the temperature of the medium it is traveling in. Some neutrons are released as 'thermal', others are released as 'fast' (like from a fission reaction).

    Water is good in reactors and for shielding of neutrons because it contains hydrogen, and hydrogen is good for three reasons. One, as you mentioned, it is approximately the same mass as a neutron. Think of billiard balls. If you have one very fast ball, and a lot of slow balls, after very few collisions you have a lot of moderate speed balls. In cases of heavier elements, think of bowling balls with the billiard ball... It takes a lot of collisions to reduce the speed.

    The second reason hydrogen is good for reactors is that it doesn't absorb neutrons very easily. (if you wanted just shielding from neutrons, you would maybe use boron, which is an excellent and cheap neutron absorber.) And the third reason is that it tends to reflect neutrons very readily. Other elements work better (like heavy water), but water is the cheapest.

    Lead tends to be stable. But it isn't completely stable unless you have old lead, because you have trace amounts of unstable forms of lead.

    So ... back to water and neutrinos. There are other people who can speak more accurately on this than I, but I believe they are looking for a muon interaction, which comes out in light (maybe cherinkov (sp?) radiation?). So you need something that is translucent, shielded (from pesky cosmic rays), and huge. It is feasible to have a large, dark, water chamber. It isn't for most other elements.
  • Heavy water tends to consist of dueterium (sp?), one proton, one nuetron, one electron. Tritium, (one proton, two nuetrons, and one electron) is unstable, has a half life of about 13 years, and I think would be very poorly suited for a detector. (because you have so many other decay events going on.)
  • Part of the solar neutrino problem can be explained by neutrino oscillations (the conversion of one type of neutrino into another). If I'm not mistaken, most experiments look for only one type of neutrino and not the other two. Since a muon is one of the products of the interaction that the Antares project will be looking at, by conservation of lepton number, it must be only muon neutrinos that they will be be sensitive to.
  • Would that make every nuclear reactor on the planet the equivelent of a script kiddie running some kind of ping flood kill on all of the neutrinonet users? Would every card come attached to a million+ gallon pool to handle detections? If I had to guess, we won't see the aplication of neutrinos in our lifetime. W
  • Do you have a hairball caught in your throat?

  • Got me..have to admit...I chuckled

  • Big problem with looking for gravitons: we haven't the faintest idea how to do it.

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