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Tetraneutron Discovered
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."
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...
Tsuyoikoto ha taisetsu da ne, dakedo namida mo hitsuyousa (Strength is an important thing, but tears too are necessary)
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...
Yes, I am an agent of Satan, but my duties are largely ceremonial.
Is this the "element 0" of fabled lore?
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.)
The living have better things to do than to continue hating the dead.
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
[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?
Life is like surrealism: if you have to have it explained to you, you can't afford it.
For all you SF fans, "spin-polarized tetraneutrons" were used in the book "Martian Rainbow" by Robert L. Forward.
I'm, Um, I'm uncertain
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)
Sometimes it's best to just let stupid people be stupid.
Maybe someone could add a small routine to Slashcode,
that just generates the appropriate Yakovism at the
bottom of the page (instead of the normal fortune).
In Soviet Russia ${NOUN} ${TRANSITIVE VERB}s you!
where NOUN, TRANSITIVE VERB are grepped from the story.
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.
- Does a tetraneutron spontaneously fly apart?
- 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?
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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.
Doesn't it make you feel good to know that our freedoms are protected by politicans, lawyers and journalists.
*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.
We've got two lives, one we're given, and the other one we make. --Mary Chapin Carpenter
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
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).
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?
Table-ized A.I.
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
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nt
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?
--Jimmy has fancy plans; and pants to match.
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.