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Science

Tetraneutron Discovered 60

Posted by michael from the lost-and-found dept.
Caid Raspa writes "According to this Press Release the French have (accidentally) produced six nuclei of tetraneutron (nucleus with four neutrons and no protons). Theoreticians have previously thought that tetraneutron does not exist. As there is no electric charge in these nuclei, they allow better studies of the nuclear forces. The scientific article is also available at arXiv.org."
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Tetraneutron Discovered More

Tetraneutron Discovered

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  • April 25? (Score:1, Offtopic)

    by CounterZer0 ( 199086 )
    So much for breaking news.....
  • Actually, the article says they may have produced some, not that they did produce some...
    The trouble with high-level physics is that theoritical models are actually built on clay... nothing is ever sure, there are always things you need to adjust, and such...

    • Re:'may have' (Score:5, Insightful)

      by alfredw ( 318652 ) <alf@freea l f . com> on Wednesday December 11, 2002 @10:48AM (#4862449) Homepage
      Actually, the article says they may have produced some, not that they did produce some...
      The trouble with high-level physics is that theoritical models are actually built on clay... nothing is ever sure, there are always things you need to adjust, and such...

      More to the point, nothing is ever certain in any science. Science can only disprove hypotheses - it can never prove anything. The language is pretty standard for researchers talking about an unconfirmed result. They're pretty sure that they got it, but until it's been checked by other independent teams, no one will consider this a done deal.

      It's just like Einstein saying he "may" have had new gravitational laws, or Pasteur saying he "may" have found a way to prevent disease. Both were sure, but the results were yet to be confirmed.

      Give 'er a year and we'll have a definitive answer.

  • IN SOVIET RUSSIA (Score:1, Funny)

    by Anonymous Coward
    This joke doesn't work with that headline.
  • I understand this is science, but is anyone else concerned with the idea of folks "accidentally" creating forms of matter? Just curious...

    • Re:Accidentally? (Score:5, Interesting)

      by dpilot ( 134227 ) on Wednesday December 11, 2002 @10:53AM (#4862485) Homepage Journal
      This was a big concern when the Large Hadron Collider was about to go into action. Some feared that the energies would be high enough to create mini black holes, which would promptly fall out of the chamber and begin eating the Earth. Eventually someone realized that higher energy collisions from cosmic rays take place above the Earth every day, and we haven't gotten eaten, yet.

      In other words, whatever we can do is already being done in that great laboratory in the sky. Literally in the sky - a few hundred miles over our heads.

      • Re:Accidentally? (Score:3, Informative)

        by Anonymous Coward
        I'm pretty sure that the controversy to which you're referring was related to the beginning of operations at RHIC, the Relativistic Heavy Ion Collider, at Brookhaven National Laboratory in New York, not the LHC, which is at CERN, in Switzerland. People (including some respected scientists) realized that there was the possibility (however slight) that at the energies reached when colliding gold ions together, "strangelets" (clumps of matter containing "strange" quarks, rather than the normal "up" and "down"), could be produced, which could potentially escape, and destroy the entire earth, yadda, yadda, yadda. Another, almost more interesting scenario, is that the collisions would be of sufficiently high energy to trigger a phase shift in teh quantum vacuum energy (kinda like when the very very early universe shifted from pure energy, and forms of matter began to appear). But, like you said, collisions with far higher energies occur every day - cosmic rays bombarding our atmosphere, mostly, so there is nothing to fear.

      • Re:Accidentally? - correction (Score:1, Informative)

        by Anonymous Coward
        The concern wan't about black-holes, it was over strange matter. The eating the earth bit is close enough. CERN gathered the worlds greatish physicst to debate the issue, and the results was that "the probabilty is very low". So there you have it.
        • The concern wan't about black-holes, it was over strange matter. The eating the earth bit is close enough. CERN gathered the worlds greatish physicst to debate the issue, and the results was that "the probabilty is very low". So there you have it.

          "Probably very low" is not very reassuring to the average person on the street. They had a fit when the Galileo probe was launched because of its nuclear power cell (and risk of contaminating Jupiter with earth life).

          I imagine the protests generated some funny cartoons. Anybody got links?
      • Not only that, but the black holes would evaporate so quickly that it's just silly. I remember back in high school I had a friend that we all joked was a 97-pound weakling. Anyway, I did a few calculations (based on Hawking's equations) and determined that if he somehow collapsed into a black hole, he would evaporate in 37 femtoseconds. (3.7x10^-14!!)

        In other words, if you were able to make 4 round trips to the moon all in a single second, by the time you'd gone the first 37 millimeters, he would already have evaporated.

        • In other words, if you were able to make 4 round trips to the moon all in a single second, by the time you'd gone the first 37 millimeters, he would already have evaporated.

          Wow, those numbers you used before were so confusing, but this analogy makes it easy for me to understand now! Thank you!!

    • Um... Penicillin? (Score:4, Interesting)

      by Theaetetus ( 590071 ) <theaetetus DOT slashdot AT gmail DOT com> on Wednesday December 11, 2002 @10:58AM (#4862530) Homepage Journal
      I understand this is science, but is anyone else concerned with the idea of folks "accidentally" creating forms of matter? Just curious...

      No... (and I know penicillin was found, not really created, but my point stands)
      I see no problem with 'creating' forms of matter, accidentally or on purpose, particularly as it can be argued that, like penicillin, these forms aren't really being created but are being discovered. They might exist elsewhere in the universe, or might have existed. And they're not really making new forms of matter - they're taking matter that already exists (neutrons) and putting them together in a way they haven't seen before (tetraneutrons). Kinda like molding sugar into cubes.

      -T

      • Re:Um... Penicillin? (Score:3, Informative)

        by bbc22405 ( 576022 )
        I see no problem with 'creating' forms of matter, accidentally or on purpose, particularly as it can be argued that, like penicillin, these forms aren't really being created but are being discovered. They might exist elsewhere in the universe, or might have existed.

        Um, you really need to work on your argument.

        First, penicillin isn't a new form of matter. It might be a new molecule, or one that mankind didn't know about before, but it doesn't rate the "new form of matter" moniker.

        Second, just because something exists somewhere in the universe does not mean that it is thus safe or wise to have it here on earth. Black holes are fine, as long as they don't come near. Quasars are fine, as long as they aren't nearby and shining at us. Supernovas? Wonderful, but please keep them many light years away.

        Maybe tetraneutron is something that is commonly made when cosmic rays hit our atmosphere, and maybe not. You should be at least a little startled by it, and that it was made _accidentally_.

        • FUD... (Score:3, Insightful)

          by Theaetetus ( 590071 )
          First, penicillin isn't a new form of matter. It might be a new molecule, or one that mankind didn't know about before, but it doesn't rate the "new form of matter" moniker.

          Check what I said - I didn't say it was a new form of matter, I said it was an accidentally discovered form of matter.

          Second, just because something exists somewhere in the universe does not mean that it is thus safe or wise to have it here on earth. Black holes are fine, as long as they don't come near. Quasars are fine, as long as they aren't nearby and shining at us. Supernovas? Wonderful, but please keep them many light years away.

          Really? Now, do you know all the properties of sub-atomic black holes? How about naked ones (no Swartzchild radius)? Quite possibly those could be pretty damn harmless - rather than simply saying "gee, the big ones are really scary, let's not even consider the little ones," doesn't it merit more study? No need for FUD here, you know. No one is claiming that they're going to make a star-sized black hole in their particle accelerator.

          Maybe tetraneutron is something that is commonly made when cosmic rays hit our atmosphere, and maybe not. You should be at least a little startled by it, and that it was made _accidentally_.

          Yes, how cool. Now, why should we be afraid of it, as grandparent suggests? It merits more study, not FUD. Thousands of other useful things were made accidentally - teflon, for one - and just because they weren't intentional doesn't mean that we should run and hide in fear from them.

          -T

          • just because they weren't intentional doesn't mean that we should run and hide in fear from them.

            But we have to protect the CHILDREN!

            -

          • Check what I said - I didn't say it was a new form of matter, I said it was an accidentally discovered form of matter.

            Penicillin isn't an accidentally discovered form of matter, it's an accidentally discovered chemical. We already knew about chemicals.

            • Penicillin isn't an accidentally discovered form of matter, it's an accidentally discovered chemical. We already knew about chemicals.

              Ohmigosh! Chemicals aren't matter? Wow! This is astounding! Here, I always thought that chemicals were matter, and you're telling me they're really energy? That's amazing!

              Point delivered, I think.

              -T

    • Leave it to the French to discover this "accidentally" .
      I've often thought that a typically French line of inquiry would be "I've never seen (bacteria - mold - fungus) do _that_ to (milk - fruit - treeroots) before, I wonder if it tastes good? Of course some of my favorite rotten milk and fruit comes from France, and you gotta love anybody who builds Citroens. On the other hand ...
  • Is this the "element 0" of fabled lore?

  • Line between Quantum and Classical (Score:5, Interesting)

    by dpilot ( 134227 ) on Wednesday December 11, 2002 @10:56AM (#4862514) Homepage Journal
    One recurring theme is where you cross the line between quantum and classical behavior. How many Fe atoms to you need before it behaves like the Iron we all are familiar with.

    This appears to be another case. At some point of glomming neutrons together you get a neutron star, though that's still an odd beast. Where do you cross the line between Tetra/Penta/Hexa-neutrons and a teeny-tiny neutron star? (I suspect this one's easy to figure, in terms balancing gravity against residual strong and weak forces, but I don't know how to do it.)

    • Re:Line between Quantum and Classical (Score:5, Informative)

      by Doctor Fishboy ( 120462 ) on Wednesday December 11, 2002 @11:53AM (#4862990)
      You're right about balancing the gravitational binding energy of a pile of neutrons with the nuclear binding energy of the same pile of neutrons. As you add more neutrons, you get to a point where the mass of the neutrons makes the gravitational binding energy pass that of the nuclear binding energy. Of course, this number of neutrons is astronomically large (pun intended).

      I did this as an undergrad problem in Nuclear physics - take a ball of N neutrons, assume nuclear type densities, and calculate the neutron ball's radius and mass (and thus it's gravitational binding energy = G * M(neutron) * N /Radius).

      When you balance this with the typical binding energy per neutron (erm, cant remember the numbers we used, sorry), you get two simple equations and you solve for N the number of neutrons.

      AFAI remembber, you get a radius of 10km and about 2 solar masses - pretty damn good for a back of the envelope calculation!

      If I can dig out the old problem sheet, I can post the number later....

      Dr Fish

  • Dumb question for the physicists out there (Score:3, Insightful)

    by DuckDuckBOOM! ( 535473 ) on Wednesday December 11, 2002 @11:04AM (#4862579)
    [restoring 7-track 150bpi high-school physics backup]
    Neutrons' function in a nucleus is supposedly to provide strong nuclear force to help counteract the protons' mutual repulsion. Seems to me that, without protons, neutrons should stick together even more readily.
    So why aren't we finding small (or sometimes not-so-small) clumps of neutrons all over the place?

    • Re:Dumb question for the physicists out there (Score:5, Informative)

      by Stevis ( 69064 ) on Wednesday December 11, 2002 @11:12AM (#4862665) Homepage
      A single neutron, not bound to a proton, is not stable against decaying into a proton. (It's oh-so-slighlty more massive than the proton.) Half-life is on the order of minutes (it's been years since I did nuclear research in undergrad and the exact #'s are escaping me). In a nucleus it's stablizied because if it decayed, the electrical repulsion between the old protons and new proton would be to great, so it's more stable if it remains a neutron. Presumably, these neutrons would also decay, and you might expect (if the 4 nucleons remained together) to see it decay to 4He (ie 2 protons and 2 neutrons)--I don't know if Hydrogen 4 has any stability, but I don't think so.

      • beta-stability versus particle-emission stability (Score:5, Informative)

        by bcrowell ( 177657 ) on Wednesday December 11, 2002 @02:36PM (#4864598) Homepage
        There are two separate issues:
        1. Does a tetraneutron spontaneously fly apart?
        2. Does a tetraneutron undergo beta decay?
        The second question doesn't even make sense to ask unless the answer to the first question is no. Until this experiment, nuclear physicists were pretty much convinced that the first answer was yes, which makes the second question nonsensical. Process #1 works via the strong nuclear force, so the time-scale for it to happen is simply the size of the nucleus divided by the typical speed of the neutrons, which is about (10^-15 m)/(10^6 m/s)=10^-21 s. Process #2 works via the weak nuclear force, so the time-scale is much longer --- probably on the same order of magnitude as the beta-decay lifetime of nuclei like 6He, which is maybe 10^-3 s.

        Since the paper appears to establish that process #1 does not happen, process #2 is what must happen. There is no doubt at all about its being beta-stable --- it's not.

        So to answer the original poster's question, here's why people were expecting that the tetraneutron would fly apart. The reason is the Heisenberg uncertainty principle plus the Pauli exclusion principle. If you try to corrall 4 neutrons into a nucleus, their small delta-x requires a large delta-p. That's why they're moving at ~1% of the speed of light. Since they're moving so fast, their attraction might not be enough to hold them together.

        So far, this reasoning applies to 4He just as much as it applies to a tetraneutron. So why would 4He be so much more stable? Well, the Pauli exclusion principle says that in a tetraneutron, the first two neutrons can both go in the lowest energy level, with their spins in opposite direction, but the third and fourth have to go in a higher energy level.

        The real question is whether the experiment is right or not. Neutron detection is notoriously difficult. In their paper, they go to great lengths to try to show that it wasn't just four neutrons from unrelated events that happened to hit the same detector --- a random coincidence. Their arguments appear convincing, but it's the kind of thing that you could easily get wrong. I'd like to see it reproduced at another lab. If it is correct, then the next step is to start measuring the properties of element zero (zeronium?). What's its lifetime? Its binding energy? Its rms radius? Does it have any bound excited states?

        • *whacks forehead*

          I told you it's been too long; of course the energy level structure is why you'd expect it to decay to 4He if it held together long enough.

          We used to do 2-neutron correlation out of heavy ion collisions, and even that required a good timing signal on when the beam pulse arrived on target so we could eliminate detections clearly not from the reaction (eg, if it arrived such that its speed was greater than c, we knew it wasn't from the reaction). This "time of flight" was also how we energy callibrated.

          The detectors we used (for the unitiated reading this) were big jars of napthalene. Large organic molecule=lots of protons for neutrons to hit---then the smacked protons gave off light as they moved, which gets collected. Never break one of these; you smell for weeks. Take it from one who knows.
        • So far, this reasoning applies to 4He just as much as it applies to a tetraneutron. So why would 4He be so much more stable? Well, the Pauli exclusion principle says that in a tetraneutron, the first two neutrons can both go in the lowest energy level, with their spins in opposite direction, but the third and fourth have to go in a higher energy level.

          By this reasoning, we'd expect 2n to be much more stable than 4n. Has this construct been produced and studied?

          Lastly, what could we expect for 3n, 5n, and 6n? Would the odd number of nucleons make 3n less stable (vs. the strong force) than 4n due to some shell-filling rule? Ditto 5n vs. 6n? Would 6n be more or less stable (vs. the strong force) than 4n? (more particles to mutually attract, but more of them in the higher energy shell).

          My apologies for being a pest, but I've been interested in the subject for quite a while, but lack the background to derive the numbers for myself (went into engineering, not physics).

          • Re:beta-stability versus particle-emission stabili (Score:4, Informative)

            by bcrowell ( 177657 ) on Wednesday December 11, 2002 @09:08PM (#4867775) Homepage
            By this reasoning, we'd expect 2n to be much more stable than 4n. Has this construct been produced and studied?
            The best evidence is that the dineutron is unbound. That's why this is an extremely surprising result. The paper does say that calculations can produce a bound tetraneutron, but the problem is that the calculations depend a lot on the parameters you assume for the strong force.

            Lastly, what could we expect for 3n, 5n, and 6n? Would the odd number of nucleons make 3n less stable (vs. the strong force) than 4n due to some shell-filling rule? Ditto 5n vs. 6n?
            Pairing means that evens are always more bound than odds. I don't think there's a chance in hell that the 3n, etc. are bound.

            Would 6n be more or less stable (vs. the strong force) than 4n? (more particles to mutually attract, but more of them in the higher energy shell).
            Yeah, interesting question. Since theorists didn't think 4n was bound, I don't think they're ready to predict whether 6n is or not :-)

        • If it is correct, then the next step is to start measuring the properties of element zero (zeronium?)

          Neutronium. If you'd spent a little less time with dusty old physics books, and more time with bold, fun comic books, you'd know that, wouldn't you?
    • Yup, absolutely right. The half life of a neutron is about 12 minutes. More interestingly, here is a test for anyone who is feeling brave: Why is the half life of a neutron 12 minutes and not 10 nanoseconds like it should be considering it decays via the weak interacation? I was asked that on my PhD oral qualifying exam...

  • Paging Dr. Forward! (Score:3, Interesting)

    by TheSHAD0W ( 258774 ) on Wednesday December 11, 2002 @11:21AM (#4862742) Homepage
    For all you SF fans, "spin-polarized tetraneutrons" were used in the book "Martian Rainbow" by Robert L. Forward.

    • Re:Paging Dr. Forward! (Score:2, Informative)

      by foolish ( 46697 )
      Erm, well you won't have any luck paging Forward. He died about 2-3 months ago from a Brain tumor/cancer.
      • Yeah, he died last September. The SFWA wrote a nice little bio on him here [sfwa.org], in which they said, "The science in his books has often been novel enough that many of his fiction books have been referenced in journal publications as 'prior art publications'." He was a very bright man. I remember writing a paper in university on zero-point energy fluctuations in a vacuum, which was based on an early paper or his.
    • Was that book any good? I've read Bob's previous novels and enjoyed them for their "hard science" aspect. But I didn't pick this one up yet because the reviews at Amazon.com [amazon.com] were less than encouraging, saying that this time around, he tried for less science, more character and story, and failed miserably. Do you think that's an accurate or unfair assessment?
      • I liked it. I don't think it was his best book, but it was well worth reading.
      • If all SF writers Forward was the absolute worst at character and story. But that doesn't matter one bit. His ideas were great! It's very depressing the way people forget this when they review someone's work and that eventually it gets to the point that a great SF writer suddenly feels the need to sacrifice the science for story and character when they are completely incapable of it. The same has happened with Egan, Bear, Clarke and many others.

  • According to this Press Release the French have (accidentally) produced six nuclei of tetraneutron (nucleus with four neutrons and no protons).

    Did they surrender soon afterward?

    (sorry)

  • To call it a "nucleus" is a little off, since that implies it's at the center of something. But without a charge, it can't attract a cloud of electrons, so must exist forever naked. Perhaps "globule" would be a more apt term.

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