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Concentration of Radon in atoms per cubic meter

  1. Jan 28, 2012 #1
    1. The problem statement, all variables and given/known data

    i) The average concentration of 222Rn in air inside a building is 20Bqm-3; what is the average concentration of Rn in atoms per cubic meter?

    ii) In a sealed room of volume 50m3 what activity of 238U in a piece of porous rock would eventually give rise to this 222Rn concentration? Assume that all of the 222Rn produced in the rock escapes into the air.

    2. Relevant equations

    R=λN
    N=N0exp[-λt]
    τ=1/λ

    3. The attempt at a solution

    i) 20Bqm-3 exists in air. Since R=λN

    N=R/λ but: N = mass*NA/molar mass

    unknown mass, unknown decay constant...

    Different approach

    λ=ln(2)/half life

    unknown half life, no given mean life. Stuck.

    I'm sure I'm being stupid... I just don't see it.

    ii) Transition rate problem...not sure where to start from. Any equations I'm missing?

    Please help. Thanks in advance.
     
  2. jcsd
  3. Jan 28, 2012 #2

    phyzguy

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    Science Advisor

    You need to look up the half-life of Rn-222 in order to do the problem.
     
  4. Jan 28, 2012 #3
    It's an exam paper. All information I have is what I've written down. There must be a different approach. (unless it says in the data booklet but I doubt it)
     
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