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Homework Help: Urgent radiation question

  1. Oct 29, 2015 #1
    1. The problem statement, all variables and given/known data
    There is a radioactive source plaed in front of the GM counter to predict the kind of radiation emmitted by the source.
    1 : When the GM counter moves 5 cm away from the source, the count rate drops significantly.
    2 : When a 5mm aluminium sheet is inserted between, the count ate drops from 100 to 50 coiounts per second.
    3 : When a magnet is used, the count rate doesnt drop significantly.

    3. The attempt at a solution
    I think it will be emitting alpha and beta radiation.
    As alpha only has a few centimeters range in air, when it is moved away fro 5 cm, the rate drops significantly.
    Also, beta radiation is also emiited, as when 5mm aluminium is used, it drops from 100 to 50 counts per second, so it indicates that beta particles are blocked.
    However, I am not sure what is use of condition 3. As if a magnet is used,if it really emits alpha and beta as I mentioned above, it will be deflected by the magnetic field so the count rate should drop significantly but the case is not.
    Ok, if let say gamma radiation is emmitted with no beta, the gamma radiation will not be blocked by the 5mm aluminium.it should remain 100 counts per second. And that's why I think there is a contradiction here.
    So, what kind of radiation is emmited??
    And why when a magnet is used, the count rate doesnt decrease??
  2. jcsd
  3. Oct 29, 2015 #2
    Depending on the energy of the gamma ray 5mm of aluminum could reduce the count rate by 50%. Also when you move 5cm away from the source which is initially next to the detector the inverse square law has a substantial affect.
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