Homework Help: Concentration of Radon in atoms per cubic meter

1. Jan 28, 2012

Ryomega

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. Jan 28, 2012

phyzguy

You need to look up the half-life of Rn-222 in order to do the problem.

3. Jan 28, 2012

Ryomega

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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