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Using a Geiger–Müller tube to prove inverse square law

  1. Oct 22, 2009 #1
    1. The problem statement, all variables and given/known data

    Today our class used a Geiger–Müller tube for the first time, and we conducted a short experiment to prove that Newton's Inverse Square Law also applies to radioactivity. We recorded the number of clicks from a small sample of Strontium-90 for ten seconds at halved distances, as shown below...

    Distance from sample (m) = 0.24
    No. of clicks = 5, 6, 7, 3, 2
    Average = 4.6

    Distance from sample (m) = 0.12
    No. of clicks = 5, 13, 5, 4, 6
    Average = 6.6

    Distance from sample (m) = 0.06
    No. of clicks = 18, 21, 21, 27, 28
    Average = 23

    Distance from sample (m) = 0.03
    No. of clicks = 42, 30, 45, 50, 44
    Average = 42.2

    Distance from sample (m) = 0.015
    No. of clicks = 114, 97, 82, 96, 94
    Average = 96.6

    As you can see the number of clicks seems to be doubling as the distance is halved, not squaring as we expected. Any ideas on we were doing wrong?

    2. Relevant equations


    3. The attempt at a solution


    This is my first post on the site so I hope I have adhered to all your conventions and what not :)
  2. jcsd
  3. Oct 22, 2009 #2
    That may be due to the constant of proportionality. Can you think of a sure way to test if a given set of points follow a power law?

    Hint: It involves plotting them in a special kind of chart with special scales on the axes ;)
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