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mfb- t1_jc9pgdr wrote

> How far radon will go via diffusion until it decays in h.l. 3.8 days?

Many meters (as rms). Random air currents are the dominant effect unless you have an extremely calm room.

The scale height for nitrogen and oxygen is ~8 km, something with 7 times the mass still has ~1 km, so in perfect equilibrium you would expect the concentration to change by ~0.2% over the height of a room. In practice you never achieve such a perfect equilibrium unless you completely seal the room, keep its temperature completely constant and wait for a very long time.

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