bof wrote:

In message , The Natural
Philosopher writes

Grunff wrote:

Dave Liquorice wrote:

I guess most comes up from the ground, but what about walls made of
that nice cornish granite?

The reason suspended floors with a 'sump' arrangement work is
because radon is very heavy, and will collect at the lowest point -
even if it is coming from the walls.


Ah. I hadn't thought that through. It has to be heavy, being
radioactive...


Not necessarily, Tritium isn't.


On investigation, you are right. Tritium is both light and radioactive,
It also has a half life measured in days, so poses very little hazard.

Perhaps I should have said more exactly that 'any radioactive element
with a sufficient half life to actually be present and represent a risk
to health will be very heavy'

Tritium only occurs naturally AFAICT on account of cosmic ray
bombardment. It decays as fast as it is produced.