How sensitive are gieger counters?

  1. So obviously you've all watched a movie where some FBI dude shows up with a geiger counter and it's able to detect trace radiation on someone who has simply handled it in a briefcase or something. My question is polonium for example is found in many things including cigarettes so what is classed as a trace amount?

    I'm seeing samples being sold with an alpha activity of 0.01uCi whatever that means. Would a Geiger counter be able to pick up such a small amount? Sorry if my question doesn't make sense or is a bit vague I'm just curios as to how true movies are when relating to real scenarios
  2. jcsd
  3. Simon Bridge

    Simon Bridge 15,471
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    "Trace" is whatever the TV shows says it is.
    There is no formal, scientific, definition. It is a quantity which is "negligible" - so it depends on the context.
    It would be reasonable for "trace radiation" to be 1/10 of the EPA safe guidelines... well below background.

    Geiger counters are as sensitive as the manufacturer says it is.
    They are not the only way to detect radiation.
    uCi is "microCurie" - you can look up what it means.
    For comparison - also look up the EPA guidelines: they are set so you'd need to be exposed for over a lifetime before you have a risk of getting sick off it.
    You'll remember some fuss a while back over Texas drinking water?
    Last edited: Sep 27, 2013

  4. Thanks for the answers, and actually no I don't remember that fuss as I'm in the UK so my news is probably not your news :D
  5. Simon Bridge

    Simon Bridge 15,471
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    I'm in NZ and still managed to hear about it ;)

    UK government has similar standards to ours - available from HSE. The standards are based on studies going back to the Curies groundbreaking research and arising later from industry experience such as the radium girls'.

    As for what it means...
    See the Rad FAQ for notes on comparing different measures - in case you are used to something else.
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  6. DrDu

    DrDu 4,635
    Science Advisor

    1 Ci corresponds to 3.7 10^10 Bq or decays per second. So 0.01 uCi is 370 Bq. That's easy to detect with a Geiger counter. In fact, a Geiger counter is a very sensitive device. However, you don't get any information on the type and energy of the radiation being detected from it.
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