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mfb- t1_jc9usg6 wrote

Reply to comment by 939319 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

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.

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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.

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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.

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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.

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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.

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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.

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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.

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subnautus t1_jcaez5p wrote

3 x 10^-14 3.67 x 10^-12 Pa, actually, but I take your point.

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mfb- t1_jcalnb3 wrote

Where did that value come from?

Assuming a straight line going through (0.6, 4.6) and (1.36, -4) we reach 1000K/(293K) = 3.41 at -21.65 which means 10^(-21.6) Pa. The extrapolation that far out will come with a large uncertainty of course.

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