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Homework Help: Radioactive Decay - Tricky

  1. Apr 5, 2012 #1
    1. The problem statement, all variables and given/known data

    radioactive.png

    2. Relevant equations

    N=N0e-λt

    3. The attempt at a solution

    I can do all of part (a) but I'm stuck on part (b).

    I don't even know where to begin. I just have no idea what to make of this question.

    Could someone prod me in the right direction ?
     
  2. jcsd
  3. Apr 8, 2012 #2

    gneill

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    Staff: Mentor

    What's the expression for the activity of a sample over time, given its half-life and initial activity value?
     
  4. Apr 8, 2012 #3
    I've written down that expression in the original post.
     
  5. Apr 8, 2012 #4

    gneill

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    Staff: Mentor

    Not quite, you've written down the amount of material remaining as a function of time. The rate of decay is measured in Becquerels (Bq) and represents the instantaneous number of decays per second. It has a similar form to the equation you wrote...
     
  6. Apr 8, 2012 #5
    Its basically the same equation except N is subbed for A and N0 for A0
     
  7. Apr 8, 2012 #6

    gneill

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    Correct. And you're given a value for Ao are you not?

    What would constitute a "current" value for A that would represent a maximum deviation of 10% from Ao? Keep in mind that Ao has an initial uncertainty of 2%.
     
  8. Apr 8, 2012 #7
    So A0 = 3.5*105

    3.78*105 ? A 2% uncertainty is built into A0 so an 8% error must originate from the A ?

    So 0.08*3.5*10^5 + 3.5*10^5 = above answer ?
     
  9. Apr 8, 2012 #8

    gneill

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    You're thinking along the right lines... but keep in mind that the Activity must decrease over time. So the new value of A should be smaller than Ao.
     
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