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Homework Help: Describe absorption experiment to distinguish 3 radiations

  1. Apr 2, 2016 #1
    1. The problem statement, all variables and given/known data
    I could not fit the whole problem typed out but;

    Describe with a diagram, an absorption experiment to distingush between alpha, beta and gamma radiation.

    2. Relevant equations
    None required, written question.

    3. The attempt at a solution

    Source, absorbers placed in front of suitable detector.
    How results identify the source
    Allowance for background radiation

    The above is a more general answer.

    Could I also use the below in my answer:
    Alpha can be stopped by a sheet of paper, beta, by aluminum, and gamma by concrete.
    Geiger counter alternatively.

    I am having difficulty using a diagram too.

  2. jcsd
  3. Apr 2, 2016 #2

    Simon Bridge

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    It gets a bit tricky because a high energy alpha particle may penetrate as far as a low energy beta particle. You'll have to decide if that is important.
    The thickness of the absorber is also important ... how much paper, how much aluminium, how much concrete?

    Of course you need to be specific: you have to explain how you account for background radiation, how the absorbers identify the source type, and how you use the geiger counter.
  4. Apr 2, 2016 #3
    All good points.

    alpha ~ 0.2mm of paper
    beta ~ 1mm Pb/1-10 mm Al
    gamma ~ 1-10cm of Pb/Several m of concrete

    Measure initial count and discount it from the radiation present?

    Could you not just use paper for example, alpha wont be able to penetrate it then say that, that radiation is obviously alpha?

    THanks for your help.
  5. Apr 2, 2016 #4

    Simon Bridge

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    How far a particle penetrates depends on how much charge it has and how much kinetic energy it has.
    But you are generally correct ... if you know you have moderate energy particles, say from nuclear decay, then whatever is stopped by a sheet of paper is alphas, whatever is stopped by a few cm of iron is betas, and anything else is gammas. But this is a rule of thumb. If, for eg, you want to identify the particles in a cosmic ray source, then this rule won't work.

    Note: Gamma ray shielding is usually made out of lead.
  6. Apr 2, 2016 #5
    Interesting idea I had not thought about that.

    Yes I gather that. Thank you for your help.
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