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Thread: Radon from Uranium

  1. #1 Radon from Uranium 
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    Hi there everyone,
    just a quick 2 questions about Radon. I have been think about these questions for a while and no-one seems to know. I hope you lot can help.

    1.) How does Radon gas escape from, say, a solid block of Uranium-238 or a mineral of Uranium like Uraninite (Pitchblende), if all the atoms are blocking the way for the Radon to escape from inside the Uranium block. Because as I imagine the Uranium will decay within the block (from the inside) as well as from the outside of the block (the visible edge). So how does the Radon escape from the inside?

    2.) Also after a while Uranium decays into Radon, which is a gas. So why, after about 5 billion years, turn into stable Lead-206 and not escape into the air in the form of Radon. I always thought Radon was a gas. So the Uranium would turn into a gas surely.

    These questions may seem difficultly worded but I hope someone can help me.

    Thanks, Matt


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  3. #2  
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    Radon is only a small percentage of the decay products of Uranium:

    Uranium-238 - Wikipedia, the free encyclopedia


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  4. #3  
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    Thanks, but how does the Radon escape from within the inner atoms of Uranium if the Uranium is in a block, say. =)
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  5. #4  
    Brassica oleracea Strange's Avatar
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    Quote Originally Posted by Matt Wall View Post
    Thanks, but how does the Radon escape from within the inner atoms of Uranium if the Uranium is in a block, say. =)
    In the case of uranium metal, I assume some will diffuse out (slowly, except when it is formed near the surface or near defects in the metal). Presumably some will effectively be trapped in the bulk metal. Most radon is formed in uranium-containing minerals where there is even more opportunity for it to diffuse out.
    Without wishing to overstate my case, everything in the observable universe definitely has its origins in Northamptonshire -- Alan Moore
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  6. #5  
    Comet Dust Collector Moderator
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    Uranium blocks don't exist in nature. In the ground, it is dispersed as a small percentage of the rock.
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  7. #6  
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    The decay of the uranium atoms in the uranium dioxide crystal would tend to disrupt the crystal structure, I assume. There would also be the pressure from the radon gas that is formed.

    Uranium-235 has a half-life of about 7.13 × 10^ 8 years, and uranium-234 has a half-life of about 2.48 × 10^ 5 years. So after 5 billion years, most of it is gone. But, it will never all go away because it is an exponential decay function.

    The radon does excape into the air. Sometimes it seeps into your basement, which is why people have their homes tested for radon.
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  8. #7  
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    Quote Originally Posted by Harold14370 View Post
    Sometimes it seeps into your basement, which is why people have their homes tested for radon.
    Also wells.
    Meteorologist/Naturalist & Retired Soldier
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  9. #8  
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    Helium is a smaller atom formed by similar means which can be trapped in the bowels of the earth. Gas atoms are more mobile by their nature but this does not imply they are never trapped by geological means- it may well occur that a radon atom decays to lead having moved very little.
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  10. #9  
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    Quote Originally Posted by Harold14370 View Post
    But, it will never all go away because it is an exponential decay function.
    Just to be picky and annoying i thought i'd point out that while the exponential decay function is a continuous function that asymptotically approaches zero, never quite reaching it as you said, the process that it models is a discrete process. ie. you can't have half an atom decay. So at some point all of the atoms will have decayed into other elements or isotopes, according to the continuous model this would have occurred after the time where is the radioactive half life. (But this may well be an upper bound on the time taken for all of the particles to decay)

    EDIT: Are we experiencing latex issues at the moment?
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  11. #10  
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    Thanks guys for your help.
    Matt =)
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