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B Does speed increase ionizing power

  1. Nov 6, 2016 #1
    Some said alpha particles are released in high speed so that it has a high ionizing power. But some said alpha particles (~10% light speed) have higher ionizing power than beta particles (~30% light speed) because it is slower, so it gives more time for it to ionizing surrounded air particles.
    So ionizing power increases with increasing speed ,or decreases with increasing speed?
  2. jcsd
  3. Nov 6, 2016 #2


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    hi there

    you are coming from a slightly incorrect premise

    Their velocity is reasonably constant within a range of around 5 - 7 % the speed of light, but what makes them highly ionising is because of their double positive charge, large mass (compared to a beta particle) and because they are relatively slow. They can cause many ionisations within a very small distance. This gives them the potential to do much more biological damage ( damage to living tissue) for the same amount of deposited energy. Alpha particles don't travel very far because they quickly pick up free electrons and become stable Helium atoms.
    They are easily stopped by a sheet of paper. Alpha particles will do the most damage to tissue when they are swallowed (ingested) when their emission is directly into tissue.

    Beta particles on the other hand are much faster but are much smaller ... they are emitted as forms of electrons. And even tho they are very high speed, because of their smaller charge and size, they are only moderately ionising

    Last edited: Nov 6, 2016
  4. Nov 6, 2016 #3
    Thanks for your reply, apart from other factors,
    Why do ionising radiation usually have high speed?
  5. Nov 6, 2016 #4


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    the velocities of the particles are what they are
    it's like asking why is the speed of light what it is ? ... that's just the way it is :wink:

    so you have 3 forms of ionising radiation

    1) Alpha ... ~ 5 - 7 % of speed of light
    2) Beta .... can be up to 75% of speed of light (in a vacuum) ( google Cherenkov radiation)
    3) Gamma rays ( are photons) so they are the speed of light in a vacuum

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