Thanks ^^
I’m aware of that now, but I didn’t know at first, so I was like “Whaaat…?”
And it used to be that people could just append quoted material with “QFT” (quoted for truth) to prevent people doing that… But I guess people can append anything with “QFT” so that wouldn’t work if what they quoted was never said… So I guess preventing editing is the only way to really prevent it… sigh…
Well, he said “IIRC” (“if I remember correctly”), so I’m betting he doesn’t have/remember the source, and there’s always the chance that his recollection is wrong. I’m sure that you could find info on it if you looked it up.
Searching, I found this:
Underlining mine. This article may be about growth in hot conditions, but it does compare the effects to those of growing in heavy water.
In general, enzymes and other organic processes select for lighter isotopes. That’s because lighter isotopes react slightly faster than heavier ones do. This is good for life because lighter isotopes tend to be less radioactive than heavier ones.
However, using this for the heavy isotope enrichment of the environment is not really going to work at all effectively. Assuming you have some situation where the light isotope bacteria or plants or whatever are mostly sequestered when they die, there’ll be a slight increase in heavy isotopes after a long time. Probably much less than the first stage of the industrial heavy water enrichment process mentioned above. And then something like erosion or vulcanism comes along and releases the sequestered material which undoes the whole thing and you’re back to square one.
Nothing to see here.
Huh?
Don’t forget that these are aliens living on what is likely a totally different planet with a totally different environment, and therefore different needs and selective pressures. They might live in an environment where it’s actually better to have slower reactions. In which case, perhaps they would sequester deuterium/heavy water, and then the non-sequestered protium/light water would evaporate out of the atmosphere…? But it still wouldn’t make more deuterium, just result in a higher concentration relative to protium… I’m still wondering if my neutron bombardment theory could possibly ever work… Are there any situations where deuterium could be one of the daughter nuclides of a fission reaction?? Whether it’s spontaneous or whether it’s bombarded by something…could that EVER happen??
Anybody there…? D’X
I’m wondering what the heck would make heavy water alkaline? Is it that when D[sub]2[/sub]O dissociates, OD[sup]-[/sup] is counted as a hydroxl but the D[sup]+[/sup] is not counted as a hydrogen ion?
Or is heavy water DOH which dissociates as D[sup]+[/sup] + OH[sup]-[/sup] in preference to H[sup]+[/sup] + OD[sup]-[/sup]?
Or a third alternative: heavy water dissociates slightly less readily than H[sub]2[/sub]O and so the concentration of ions is slightly lower.
I’m curious if conditions on a “marginal atmosphere” world – one barely massive enough to retain an atmoshere, like Mars – might be such that protium, protium oxide, etc., might be preferentially lost, leading to a relative enrichment of deuterium, its oxide, etc.
Basically. It appears that the self-ionization constant for water slightly changes as its mass increases: See Self-ionization of water - Wikipedia and near the end “Isotope effects”. The pH is higher where the concentration of ions is lower as it is the negative logarithm of the concentration. Note that the ratio of H[sub]3[/sub]O and OH will be the same, but they will each be lower - and that’s what’s measured by pH. The problem is that a pH measurement assumes you have standard water, and in this case you don’t. Your meter may register slightly basic, but it won’t mean that it actually acts that way chemically.
Deleted - created a new thread instead as intended
What come to mind is a natural nuclear reactor where neutrons are regularly released in contact with water, if the water would absorb the extra neutron. Not sure it works that way. but natural nuke reactors do occur:
Certainly H[sub]2[/sub] would be preferentially lost relative to D[sub]2[/sub] (or DH) as it is lighter by 50% (or 67%). At the same kinetic energy, the average speed of an H[sub]2[/sub] molecule would be 41% faster than a D[sub]2[/sub] molecule and so more likely to escape the atmosphere.
This would work much better to concentrate the deuterium before it was combined into heavy water though where the weight difference is only about 10% or 5% depending on whether its one of two deuterium atoms in the heavy water.
No one commented on this in the month and a half the thread was in the grave, so I’ll give it a shot. I just saw the thread, today, so I didn’t have a chance to say anything before.
I studied chemistry in college, and I spent 13 years working in a field where we used nuclear machines that emitted gamma and neutrons to measure their stuff, so I learned a few things about it from the required certification courses.
Neutron activation: Our machines measured the amount of hydrogen, the more hydrogen in detection range, the higher the reading, because the fast neutrons the machine emitted would not be picked up by the detector, but the ones that had bounced off of hydrogen nuclei a few times would slow down to something that would be detected. They don’t stick, they bounce. Neutron activation of water won’t work. As a curious aside, I had an aluminum notebook holder that I always left next to the machine when not in use. After a number of years, it gave off more radiation than other people’s who didn’t leave theirs next to the machines. Neutron activation in action. 
Indeed, many nuclear reactors are of the light-water design, because water has so little tendency to absorb neutrons.
Too late to edit: it does absorb enough neutrons that light-water reactors have to use enriched fuel; I believe the natural reactors only worked in the past because U-235 was more common hundreds of millions of years ago.
Don’t ice cubes made with heavy water sink instead of floating?
Enzymes can strongly favor one isotope over another. For non-tunneling processes, the maximum kinetic isotope effect is ~7 IIRC due to differences in zero point energies of C-H vs C-D bonds but very small differences in the energies of the transition states for bond breaking. However, if the chemical process involves tunneling (H moves “through” the energy barrier rather than over it), KIEs can be huge. 30-50 is common. I think the record is 100 or so.