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Stable nucleons other than Neutrons and Protons?

  1. Jun 16, 2010 #1
    Can there be any particle other than a proton or a neutron that can remain stably in the nucleus of an atom at ordinary temperatures and pressures?

    I'm aware of hypernuclei (nuclei containing hyperons) but none of those are stable. I understand that they all decay weakly.

    Is there any event known in the universe, however rare, that can create stable nuclei containing nuclear particles other than neutrons and protons at ordinary temperatures and pressures?

    Thanks
     
  2. jcsd
  3. Jun 17, 2010 #2

    phyzguy

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    Two points that you may not be aware of:

    (1) Free neutrons are not stable - they decay into a proton, an electron, and an electron anti-neutrino with a half-life of abut 15 minutes.

    (2) Within a stable nucleus, I don't think that the protons and neutrons that it is composed of retain their identities. It is basically a swarm of quarks and gluons that form into different combinations over time. So I don't think we can really say that a given nucleus (iron for example) has discrete protons and neutrons within it.

    So back to your question. If I take an alpha particle (helium nucleus) as an example. It is typically built up from two protons and two neutrons. However, I think if you built it up from other hadrons that you would get the same result, as long as it had the correct number of up and down quarks.
     
  4. Jun 17, 2010 #3

    Meir Achuz

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    There are no stable nuclei with any basic particles other than p and n.
    However, nuclear wave functions do include admixtures of other hadrons, especially the pion and Delta.
     
  5. Jun 17, 2010 #4

    Vanadium 50

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    You can scatter something off a single nucleon in a nucleus.
     
  6. Jun 17, 2010 #5

    phyzguy

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    There clearly are protons and neutrons present in a nucleus. My point is that I don't think the protons and neutrons retain their identities over a long period of time. The quarks are moving around so that if you could track a single quark over a period of time, it would sometimes be part of a proton, sometimes part of a neutron, sometimes part of a pion, and so on. So to ask whether nuclei can be composed of particles other than protons and neutrons I think is not really asking the right question.
     
  7. Jun 17, 2010 #6

    tom.stoer

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    Effectively there are strongly coupled protons and neutrons interchanging pions which turns protons into neutrons and vice versa. The pion exchange is reflected by the pion mass entering the Yukawa potential. Of course there are also corrections of heavier meson states.

    Of course these interactions are only low-energy effective models based on quarks and gluons. But protons and neutrons remain a reasonable effective degrees of freedom; at much higher energy densities they disintegrate into quark-gluon plasma.
     
  8. Jun 17, 2010 #7

    tom.stoer

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    Why?

    Isn't it possible to prepare a nucleus striping of an s-quark from a scattering hadron with strangeness, e.g. in a low-energy collision? The lifetime of the resulting nucleus would have to be much higher than the lifetime of the s-quark; but this could work as the s-quark decays only weakly.
     
  9. Jun 17, 2010 #8

    Meir Achuz

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    There are hypernuclei which, as you say, decay weakly.
    That is why I said "stable".
     
  10. Jun 18, 2010 #9

    tom.stoer

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    thanks
     
  11. Jun 20, 2010 #10

    bcrowell

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  12. Jun 21, 2010 #11
    So what you guys are effectively saying is that J J Thomson was right all along!

    http://en.wikipedia.org/wiki/Plum_pudding_model
     
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