# 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?

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)