Teo_Filin t1_jc9mf6h wrote
Reply to comment by mfb- in Radon is a monatomic gas, but its decay products are solids. After a decay, what happens to the individual atoms of the daughter elements? Do they stay suspended in the atmosphere or slowly rain out? by foodtower
Randomly like others? What about prevailing gravity force for such heavy particles?
mfb- t1_jc9n2sg wrote
Doesn't play a big role over the size of a room. Random air currents and even diffusion are more important. If you release a heavy atom in the middle of a room it's slightly more likely to hit the ground first instead of the ceiling but the difference is just something like 0.1% or less.
939319 t1_jc9uamt wrote
?? are you saying lead can be a (very low partial pressure) gas at STP?
mfb- t1_jc9usg6 wrote
With lead alone almost all atoms would hit the wall and freeze out in milliseconds, although theoretically the vapor pressure is not zero. With other gases you can have lead in there for a while outside of equilibrium.
foodtower OP t1_jcagoi2 wrote
What I'm gathering is that in normal air it would mostly cling on to dust particles, in dust-free air it would be an extremely low-partial-pressure gaseous component, and in pure form (say, a container of pure radon that decays) nearly all of it would attach to container walls, leaving an extremely low-pressure lead gas behind.
mfb- t1_jcah6mi wrote
Right.
drsoftware t1_jcb339z wrote
However, there are a lot more more oxygen atoms to collide with. Given mean free path and velocity at standard temperature and pressure, I think the random movement of the Pb atom is more likely to react with oxygen before finding the dust particle. Another response calculated the Pb O reaction to occur with in a second.
Dd_8630 t1_jc9zqoa wrote
Not necessarily milliseconds. It can take minutes for an atom of gad in STP atmosphere to bumble its way to a room's wall.
mfb- t1_jca0ls4 wrote
The first sentence was discussing a scenario where we only have the lead atoms (at their extremely low density) and nothing else. I added the remaining gases back in the second sentence.
subnautus t1_jcab5bu wrote
If the scenario only takes the presence of lead into account, there's still a decent probability of lead vapor existing. You figure the vapor pressure of mercury is so well documented by experiments where ullage develops in a container filled in such a manner where no material other than mercury could be present; the same should be true of all materials subject to vacuum.
Or, put another way, your suggestion that lead would "freeze out" as soon as it hits the wall of its container suggests you could hit absolute vacuum (and thus absolute zero temperature) by simply waiting.
mfb- t1_jcabtfm wrote
I already mentioned that, too...
> With lead alone almost all atoms would hit the wall and freeze out in milliseconds, although theoretically the vapor pressure is not zero.
The vapor pressure of lead at room temperature is absurdly small. Something below 10^(-20) Pa extrapolating from this graph.
[deleted] t1_jcags1v wrote
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skyler_on_the_moon t1_jc9zh92 wrote
Every element and compound can be, it's just that for most solids the partial pressure is so low as to be negligible.
Teo_Filin t1_jc9ovzp wrote
So 7x mass nearly doesn't matter.
How far radon will go via diffusion until it decays in h.l. 3.8 days? Its products are to be bound faster, I suppose.
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.
[deleted] t1_jcaj15r wrote
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