# Something I'd love to know about heavy water… **URL:** \ **Category:** Factual Questions\ **Created:** [September 10, 2010, 2:15pm UTC](https://boards.straightdope.com/t/something-id-love-to-know-about-heavy-water/553288 "2010-09-10T14:15:20Z")\ **Posts on this page:** 19\ **Page:** 3
**Author:** ![NoriMori](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/norimori/32/13254_2.png) [@NoriMori](https://boards.straightdope.com/u/NoriMori)\ **Post date:** [September 14, 2010, 2:08am UTC](https://boards.straightdope.com/t/something-id-love-to-know-about-heavy-water/553288/41 "2010-09-14T02:08:57Z")
> [@Der\_Trihs](#): > > > [@NoriMori](#): > > > > EDIT: Hey… How come I can edit this post but not the two previous ones?? O.o > > It’s timed, you have only a 5 minute period to edit anything. This keeps dishonest people from editing their own previous statements in debates and claiming that they never said what they are accused of; something I’ve seen on boards that allow unlimited editing. 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_… ---
**Author:** ![NoriMori](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/norimori/32/13254_2.png) [@NoriMori](https://boards.straightdope.com/u/NoriMori)\ **Post date:** [September 14, 2010, 2:12am UTC](https://boards.straightdope.com/t/something-id-love-to-know-about-heavy-water/553288/42 "2010-09-14T02:12:18Z")
> [@Todderbob](#): > > > [@Der\_Trihs](#): > > > > IIRC bacteria tend to grow huge for example. Well, huge for bacteria. > > cite? 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. ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [September 14, 2010, 9:03am UTC](https://boards.straightdope.com/t/something-id-love-to-know-about-heavy-water/553288/43 "2010-09-14T09:03:37Z")
> [@Todderbob](#): > > > [@Der\_Trihs](#): > > > > IIRC bacteria tend to grow huge for example. Well, huge for bacteria. > > cite? Searching, I found [this](http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6T1W-47DTTXD-7N&_user=10&_coverDate=05%2F14%2F1968&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_searchStrId=1460355777&_rerunOrigin=google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=81bb29ce46b10e35eb584c3645d534eb&searchtype=a): > [@](#): > > Several strains of Bacillus subtilis, which normally are mesophilic bacteria, can be adapted to grow at elevated temperatures, as high as 72°, by slowly increasing the temperature of incubation. Organisms adapted to growth at 63° are about 3–5 times larger than organisms growth at 37°. The amount of DNA and RNA per organism is approximately the same when growth at 63° as when grown at 37°, but bacteria adapted to growth at high temperatures contain increased amounts of protein per cell. When bacteria adapted to growth at elevated temperatures are subsequently grown at 37°, the ability to grow at high temperatures is lost and the bacteria must be readapted. The phenomenon appears to resemble bacterial adaptation to growth on heavy water or trifluoroleucine rather than the result of mutation. Underlining mine. This article may be about growth in hot conditions, but it does compare the effects to those of growing in heavy water. ---
**Author:** ![dtilque](https://avatars.discourse-cdn.com/v4/letter/d/d6d6ee/32.png) [@dtilque](https://boards.straightdope.com/u/dtilque)\ **Post date:** [September 14, 2010, 9:20am UTC](https://boards.straightdope.com/t/something-id-love-to-know-about-heavy-water/553288/44 "2010-09-14T09:20:00Z")
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. ---
**Author:** ![Nava](https://avatars.discourse-cdn.com/v4/letter/n/da6949/32.png) [@Nava](https://boards.straightdope.com/u/Nava)\ **Post date:** [September 14, 2010, 9:55am UTC](https://boards.straightdope.com/t/something-id-love-to-know-about-heavy-water/553288/45 "2010-09-14T09:55:08Z")
Nothing to see here. ---
**Author:** ![NoriMori](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/norimori/32/13254_2.png) [@NoriMori](https://boards.straightdope.com/u/NoriMori)\ **Post date:** [September 15, 2010, 2:47pm UTC](https://boards.straightdope.com/t/something-id-love-to-know-about-heavy-water/553288/46 "2010-09-15T14:47:17Z")
> [@Nava](#): > > Nothing to see here. Huh? > [@dtilque](#): > > 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. 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?? ---
**Author:** ![NoriMori](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/norimori/32/13254_2.png) [@NoriMori](https://boards.straightdope.com/u/NoriMori)\ **Post date:** [November 2, 2010, 3:51am UTC](https://boards.straightdope.com/t/something-id-love-to-know-about-heavy-water/553288/47 "2010-11-02T03:51:49Z")
Anybody there…? D’X ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [November 2, 2010, 4:24am UTC](https://boards.straightdope.com/t/something-id-love-to-know-about-heavy-water/553288/48 "2010-11-02T04:24:33Z")
> [@NoriMori](#): > > Wikipedia has a chart of physical differences between them: > > pH (at 25°C) 7.41 7.00 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]? ---
**Author:** ![Malacandra](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Malacandra](https://boards.straightdope.com/u/Malacandra)\ **Post date:** [November 2, 2010, 9:30am UTC](https://boards.straightdope.com/t/something-id-love-to-know-about-heavy-water/553288/49 "2010-11-02T09:30:04Z")
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. ---
**Author:** ![Polycarp](https://avatars.discourse-cdn.com/v4/letter/p/82dd89/32.png) [@Polycarp](https://boards.straightdope.com/u/Polycarp)\ **Post date:** [November 2, 2010, 1:14pm UTC](https://boards.straightdope.com/t/something-id-love-to-know-about-heavy-water/553288/50 "2010-11-02T13:14:26Z")
> [@Chronos](#): > > The proportion of hydrogen that is deuterium might be larger on Venus than it is on Earth, but it’s still pretty small. I don’t think there’s any place known in the Universe, outside of a laboratory, where deuterium is more common than normal hydrogen. 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. ---
**Author:** ![glowacks](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/glowacks/32/5548_2.png) [@glowacks](https://boards.straightdope.com/u/glowacks)\ **Post date:** [November 2, 2010, 4:00pm UTC](https://boards.straightdope.com/t/something-id-love-to-know-about-heavy-water/553288/51 "2010-11-02T16:00:36Z")
> [@Malacandra](#): > > 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. Basically. It appears that the self-ionization constant for water slightly changes as its mass increases: See [Self-ionization of water - Wikipedia](http://en.wikipedia.org/wiki/Self-ionisation_of_water) 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. ---
**Author:** ![glowacks](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/glowacks/32/5548_2.png) [@glowacks](https://boards.straightdope.com/u/glowacks)\ **Post date:** [November 2, 2010, 4:40pm UTC](https://boards.straightdope.com/t/something-id-love-to-know-about-heavy-water/553288/52 "2010-11-02T16:40:17Z")
Deleted - created a new thread instead as intended ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [November 2, 2010, 5:09pm UTC](https://boards.straightdope.com/t/something-id-love-to-know-about-heavy-water/553288/53 "2010-11-02T17:09:45Z")
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: > **[Natural nuclear fission reactor](https://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor)** > > A natural nuclear fission reactor is a uranium deposit where self-sustaining nuclear chain reactions occur. The conditions under which a natural nuclear reactor could exist had been predicted in 1956 by Paul Kuroda. The remnants of an extinct or fossil nuclear fission reactor, where self-sustaining nuclear reactions have occurred in the past, can be verified by analysis of isotope ratios of uranium and of the fission products (and the stable daughter nuclides of those fission products). An exa Ok... ---
**Author:** ![OldGuy](https://avatars.discourse-cdn.com/v4/letter/o/3bc359/32.png) [@OldGuy](https://boards.straightdope.com/u/OldGuy)\ **Post date:** [November 3, 2010, 9:12pm UTC](https://boards.straightdope.com/t/something-id-love-to-know-about-heavy-water/553288/54 "2010-11-03T21:12:03Z")
> [@Polycarp](#): > > 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. 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. ---
**Author:** ![Cheshire\_Human](https://avatars.discourse-cdn.com/v4/letter/c/5f8ce5/32.png) [@Cheshire\_Human](https://boards.straightdope.com/u/Cheshire_Human)\ **Post date:** [November 4, 2010, 12:14am UTC](https://boards.straightdope.com/t/something-id-love-to-know-about-heavy-water/553288/55 "2010-11-04T00:14:15Z")
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. > [@NoriMori](#): > > “In health physics neutron radiation is considered a fourth radiation hazard alongside the other types of radiation. Another, sometimes more severe hazard of neutron radiation, is neutron activation, the ability of neutron radiation to induce radioactivity in most substances it encounters, including the body tissues of the workers themselves. This occurs through the capture of neutrons by atomic nuclei, which are transformed to another nuclide, frequently a radionuclide. This process accounts for much of the radioactive material released by the detonation of a nuclear weapon. It is also a problem in nuclear fission and nuclear fusion installations, as it gradually renders the equipment radioactive; eventually the hardware must be replaced and disposed of as low-level radioactive waste.” > ~ Wikipedia, “Neutron radiation” > > It seems that a lot of materials absorb neutrons pretty easily. Why is it so difficult for hydrogen? > > If water were bombarded with neutrons like in the situation I described in my previous post, could it eventually become heavy water? 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. 🙂 ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [November 4, 2010, 3:36am UTC](https://boards.straightdope.com/t/something-id-love-to-know-about-heavy-water/553288/56 "2010-11-04T03:36:40Z")
Indeed, many nuclear reactors are of the [light-water design](http://en.wikipedia.org/wiki/Light_water_reactor), because water has so little tendency to absorb neutrons. ---
**Author:** ![Lumpy](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lumpy/32/446_2.png) [@Lumpy](https://boards.straightdope.com/u/Lumpy)\ **Post date:** [November 4, 2010, 3:44am UTC](https://boards.straightdope.com/t/something-id-love-to-know-about-heavy-water/553288/57 "2010-11-04T03:44:10Z")
> [@Lumpy](#): > > Indeed, many nuclear reactors are of the [light-water design](http://en.wikipedia.org/wiki/Light_water_reactor), 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. ---
**Author:** ![Saint\_Cad](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/saint_cad/32/18907_2.png) [@Saint\_Cad](https://boards.straightdope.com/u/Saint_Cad)\ **Post date:** [November 4, 2010, 3:04pm UTC](https://boards.straightdope.com/t/something-id-love-to-know-about-heavy-water/553288/58 "2010-11-04T15:04:15Z")
> [@Lust4Life](#): > > O.T. but what is Heavy Water like I.R.L. ? > > Does it look the same as normal water, weigh the same, move the same ? > > A naive question I know but its something that I’ve always been curious about. Don’t ice cubes made with heavy water sink instead of floating? ---
**Author:** ![Ruken](https://avatars.discourse-cdn.com/v4/letter/r/f475e1/32.png) [@Ruken](https://boards.straightdope.com/u/Ruken)\ **Post date:** [November 4, 2010, 4:10pm UTC](https://boards.straightdope.com/t/something-id-love-to-know-about-heavy-water/553288/59 "2010-11-04T16:10:59Z")
> [@Visual\_Purple](#): > > Here’s a half-baked idea. NoriMori said abiotic processes, but would s/he be willing to accept ones involving simple life forms? Don’t enzymes often slightly favor one isotope over another? 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. [Previous page](https://boards.straightdope.com/t/something-id-love-to-know-about-heavy-water/553288.md?page=2)