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Stability of transuranic elements

  1. Aug 1, 2005 #1

    ACG

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    I remember hearing somewhere that one of the reasons people are trying to make elements which high atomic numbers is to see if they can be made to have long half-lives, such as uranium. In effect, they're virtually stable. However, I don't see how that can be.

    Here's why. Suppose element X has an atomic number over 100 and has a long half life. If I recall correctly, all elements higher than iron are created in supernova explosions when lots of neutrons and protons starts crashing into each other in extreme conditions. The only way for this element to not exist would be for the supernova explosions to not be able to create it to begin with (otherwise, we'd see it lying around on the earth's surface just like uranium).

    This means one of two things: element X does not exist, or element X exists but cannot be created in supernovas.

    Which of these is it? Is the chain of short-half-life elements from Z=98-115 long enough that it basically serves as a bottleneck in the process a supernova uses to construct elements? Do these high-Z elements require temperatures to create which cannot be created even in a supernova?

    Thanks in advance,

    ACG
     
  2. jcsd
  3. Aug 1, 2005 #2

    Astronuc

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    WWW Chart of the Nuclides 2004

    Blocks 23-29 have actinides and transactinides, and provides half-lives. Click on each block to see individual radioactinides, and click on each radionuclide for detailed properties, such as decay mode.

    Most transactinides have short half-lives, so in millions or billions of years, most radionuclides on earth have decayed. Those in existence have long half-lives, or are decay products of those longer nuclides.
     
  4. Aug 2, 2005 #3

    Borek

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    There is a flaw in your thiniking - if the half-life is measured in millions of years isotope is relatively 'stable', but even if it produced in large amounts during Supernova explosion it has no chances to make its way to any planetary system, as these are created in much longer periods of time (not to mention the time needed for evolution to create observer skilled enough).
     
  5. Aug 2, 2005 #4

    Astronuc

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    See the related thread - elements of mother earth

    A supernova nearby a planetary system may produce heavy elements which are collected by some planets, as has been posited for the solar system.

    It is believed that the heaviest elements are produced through successive neutron capture. In the thermonuclear explosions detonated by US military, transuranic elements were produced by successive n-capture in what was initially uranium.
     
    Last edited: Aug 2, 2005
  6. Aug 2, 2005 #5

    Nereid

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    Now here's the kicker: IIRC, some *very* high A nuclei have been found in cosmic rays, as in *way* beyond U and Pu isotopes.

    That supernovae (and their remnants) can accelerate particles to extraordinarily high energies (far, far beyond what the LHC will be capable of) is pretty well demonstrated.

    That (certain) supernovae are essentially 'heavy element factories' to a degree that the directors of the best labs we have today here on Earth can only weep to contemplate is also pretty well demonstrated.

    Is there then a region of (heavy element) stability that is currently far, far beyond our grasp (here in earthly labs), but whose stability is sufficiently 'marginal' (and/or quantity of production products, measured in millions of tonnes, is sufficiently low) that we have no clear signal of their existence in our present-day Earth?
     
  7. Aug 2, 2005 #6

    Borek

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    Yes, I was writing a little bit faster then I was thinking :)

    Still, even if it is possible that such heavy elements can be produced and CAN be collected, doesn't mean they have been produced and HAVE BEEN collected in the time close enough to us - so there is still a flaw in the the OP thinking.
     
  8. Aug 6, 2005 #7
    just because an element is not naturally occuring does not necessarily mean that it cannot be made.

    according to theory, it has been predicted that there is possibly an "island of stability" out past element 120. it is difficult to know for sure, since the electronic stucture of these elements is hard to predict.

    take a look at the benfey periodic table: the hypothesized island of stability would lie on the arm labeled "superactinides":

    http://library.thinkquest.org/C0110203/othertables.htm
     
    Last edited: Aug 6, 2005
  9. Aug 7, 2005 #8

    Astronuc

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    The question is then - "what is meant by stability?" Does it mean truly stable, i.e. does not decay, or does it mean "very long half-life" on the order of 100's of millions of year or billions of years.

    The projections from the chart of nuclides indicate that superactinides may have half-lives on the order of seconds or fractions of seconds. On the other hand, it is not clear how this was determined since the radionuclides have yet to be sythesized.
     
  10. Aug 7, 2005 #9

    Janus

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    It means relative stability. It means that these nuclei would have longer lifetimes than those surrounding them; a year rather than secs.
    The process is simular to the way they could predict chemical and physical properties of elements before they were discovered.(when there were still gaps in the periodic table.)

    The islands of stability occur due to what are called the "Magic Numbers", specific groupings of protons and neutrons which tend to make the nucleus more stable (Again, something akin to the closing of electron shells of atoms.)

    The pattern predicts that such an island might exist somewhere in the transuranium elements.
     
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