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Radioactive Decay

  1. Jul 26, 2009 #1
    Can anyone tell me what makes an atom unstable, and more prone to radioactive decay? From what I've read in books and on http://en.wikipedia.org/wiki/Nuclear_decay" [Broken], it's caused by flucutations in the quantum vacuum which disturb the nucleus. But why are some atoms more prone to be bothered by this disturbance?

    Daisey
     
    Last edited by a moderator: May 4, 2017
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  3. Jul 26, 2009 #2

    Astronuc

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    Disturbances in the quantum vacuum?

    How about it comes from having too many or too few neutrons for a given number of protons, which puts the nucleus at a slightly higher energy state than more stable configurations.

    Too few neutrons, and the nucleus will undergo positron or more likely neutron capture.

    Too many neutrons will result in beta decay or alpha decay if the nucleus is of an element like Bi or heavier.
     
  4. Jul 26, 2009 #3
    Well, Yes. The exact wording in the Wikipedia article I quoted above is "In the case of an excited atomic nucleus, the arbitrarily small disturbance comes from quantum vacuum fluctuations."
     
  5. Jul 26, 2009 #4
    Is it safe to say that if a nucleus has a different number of protons than neutrons, it is unstable? Or it is true that if an atom has a different number of electrons orbiting the nucleus than it has protons in the nucleus it is unstable?

    Daisey
     
  6. Jul 26, 2009 #5
    Last edited: Jul 26, 2009
  7. Jul 26, 2009 #6
    Naty1,

    Thanks. A very nice article. :smile:

    Here is a quote from the above CreationWiki link: "The instability of a radionuclide's nucleus may result from an excess of either neutrons or protons."

    What is meant by "an excess"? Does that mean if there not exactly the same number of each?

    Daisey
     
  8. Jul 26, 2009 #7

    Vanadium 50

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    CreationWiki? The "encyclopedia of creation science"? I would not consider that a reputable source.
     
  9. Jul 26, 2009 #8
    How would creation science differ from any other regarding Radioactive Decay??
     
  10. Jul 26, 2009 #9

    DrChinese

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    Doesn't really matter. They cannot be relied upon if they sometimes change things to suit their religious beliefs.
     
  11. Jul 26, 2009 #10

    DrChinese

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    No, that is not a good rule. It is a bit complicated and there are a lot of factors. Electrons don't really fit into the equation at all.

    Almost every element has unstable isotopes. Generally, as a nucleus gets bigger than a certain size they become less stable very quickly. But a lot has to do with the shape of the nucleus and the exact mix of protons and neutrons. Adding a neutron to a stable nucleus may or may not produce a stable larger nucleus. And vice versa.
     
  12. Jul 26, 2009 #11
    Titanium (Z=22) has 5 stable isotopes. Technecium (Z=43) has none. Not all nuclei that have an equal number of neutrons and protons are stable.
     
  13. Jul 26, 2009 #12
    I thought I remember reading somewhere that for the most part all nuclei are of the same size, no matter the atomic mass.
     
  14. Jul 26, 2009 #13
    Bob, Is that also true for all elements below Bismuth (83)?
     
  15. Jul 26, 2009 #14

    Astronuc

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  16. Jul 26, 2009 #15
    Sorry. I stand corrected. I just found the quote. From Kenneth Fords book "The Quantum World", on pg 201 he states that all atoms (not nuclei) have about the same size.
     
  17. Jul 26, 2009 #16
    Astronuc,

    That is a really fine web site. I went to look for Calcium 40 on that chart, and on the Decay Mode display, it shows 40Ca not colored black, meaning it is NOT stable. It's actually colored light blue, which I believe refers to the decay mode: EC+β+ Now, 42Ca IS stable (colored black).

    Am I reading this wrong?
     
  18. Jul 27, 2009 #17

    Vanadium 50

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    Exactly. An unreliable source isn't always wrong. Just...unreliable.
     
  19. Jul 27, 2009 #18

    vanesch

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    To add my 2 cents. I think what the OP is alluding to (or at least, the article quoted by the OP is alluding to) is the fact that strictly speaking, stationary solutions of the hamiltonian are, well, stationary. So even excited states should be "stable" and remain there for ever, even if there exist lower states. But that is of course assuming that the hamiltonian describing the system is exact. The point is that, in *atomic* physics, it is the coupling to the QED field, which can be shown to be responsible for electronic transitions from excited states to ground states (spontaneous decay). I suppose (but I never read anything about it) that something similar is also at work in the nuclear case.
    So spontaneous decay is attributed to the coupling between the empty (vacuum) field and the system at hand (say, the electron cloud in the case of atomic transitions, and the nuclear structure in the case of radioactivity), and it is indeed the quantum nature of the field to which it couples which makes the transitions possible (which would otherwise remain locked up in their stationary state).
     
  20. Jul 27, 2009 #19
    Daisey-
    You've been told about nuclear beta decay, both positron and electron. But there is another form of weak interaction decay. Sometimes an atom has too many protons and not enough neutrons, and the atom would have less mass if a proton were to decay. But it cannot because it doesn't have enough extra mass to create a positron and decay. So the proton waits around and captures an atomic electron. This is called electron capture. A good example is rubidium-83 "decaying" to krypton-83.
    Here is another chart of isotopes that is easier to read:
    http://en.wikipedia.org/wiki/Table_of_nuclides_(complete [Broken])
    [Added in Edit]
    There are a class of nuclei that are much more unstable than others. They are called odd-odd nuclei, because they have an odd number of protons AND an odd number of neutrons. A few of these can radioadtively decay by emitting either a positron or electron. One of these is copper 64, with 29 protons and 35 neutrons. Copper 64-can decay 3-ways: electron emission, positron emission, or electron capture. See
    http://www.freebase.com/view/guid/9202a8c04000641f800000000bf63b1d/-/chemistry/isotope/decay_modes
     
    Last edited by a moderator: May 4, 2017
  21. Jul 28, 2009 #20
    Daisey, google shell model which explains the magic numbers (the numbers of neutrons and protons in exceptionally stable nuclei) nicely. This question of yours has been on a table for a long time.
     
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