# Do all elements have a half life?
**URL:** https://boards.straightdope.com/t/do-all-elements-have-a-half-life/347316
**Category:** Factual Questions
**Created:** [March 6, 2006, 11:33pm UTC](https://boards.straightdope.com/t/do-all-elements-have-a-half-life/347316 "2006-03-06T23:33:16Z")
**Posts on this page:** 20
**Page:** 1
### Author:  [@magellan01](https://boards.straightdope.com/u/magellan01)
#### Post date: [March 6, 2006, 11:33pm UTC](https://boards.straightdope.com/t/do-all-elements-have-a-half-life/347316/1 "2006-03-06T23:33:16Z")
Do all elements decay? or just ones that are radioactive? Do they more basic elements like hydrogen, helium, and oxyogen decay? How about water?
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### Author:  [@friedo](https://boards.straightdope.com/u/friedo)
#### Post date: [March 6, 2006, 11:49pm UTC](https://boards.straightdope.com/t/do-all-elements-have-a-half-life/347316/2 "2006-03-06T23:49:41Z")
Only radioactive elements undergo radioactive decay.
Also, water is not an element, it is a compound of hydrogen and oxygen.
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### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [March 6, 2006, 11:57pm UTC](https://boards.straightdope.com/t/do-all-elements-have-a-half-life/347316/3 "2006-03-06T23:57:24Z")
> [@friedo](#):
>
> Only radioactive elements undergo radioactive decay.
Correction: radioactive _isotopes_ undxergo radioactive decay. Even elements we normally don’t think of as radioactive may have one or more unstable isotopes. All the elemnts listed in the OP, in fact, have at least one known radioisotope.
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### Author:  [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)
#### Post date: [March 6, 2006, 11:57pm UTC](https://boards.straightdope.com/t/do-all-elements-have-a-half-life/347316/4 "2006-03-06T23:57:26Z")
> [@magellan01](#):
>
> Do all elements decay? or just ones that are radioactive? Do they more basic elements like hydrogen, helium, and oxyogen decay? How about water?
Just the ones that are radioactive. 😉 However, some of the lighter elements do have radioactive isotopes. Potassium 40 decays with a half-life of 1.3 billion years. Rubidium 87 decays with a half life of 47 billion years.
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### Author:  [@OtakuLoki](https://boards.straightdope.com/u/OtakuLoki)
#### Post date: [March 7, 2006, 12:00am UTC](https://boards.straightdope.com/t/do-all-elements-have-a-half-life/347316/5 "2006-03-07T00:00:38Z")
Has the question about proton decay been answered? I thought that there are a couple of deep pool detectors looking for signs of proton decay. If that does happen, doesn’t it mean that all matter does have a half-life? Granted, if it does happen, it’s going to make the decay of Rubidium 87 look speedy.
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### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [March 7, 2006, 12:02am UTC](https://boards.straightdope.com/t/do-all-elements-have-a-half-life/347316/6 "2006-03-07T00:02:18Z")
Sheesh, nice typing above, **Q.E.D.**! :smack:
Also, there’s some evidence that protons can decay with a hugely long half-life, but I believe that only applies to free protons, not those bound inside atomic nuclei, yes?
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### Author:  [@friedo](https://boards.straightdope.com/u/friedo)
#### Post date: [March 7, 2006, 12:06am UTC](https://boards.straightdope.com/t/do-all-elements-have-a-half-life/347316/7 "2006-03-07T00:06:05Z")
> [@Q.E.D.](#):
>
> Correction: radioactive _isotopes_ undxergo radioactive decay.
Good point! :smack:
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### Author:  [@OtakuLoki](https://boards.straightdope.com/u/OtakuLoki)
#### Post date: [March 7, 2006, 12:08am UTC](https://boards.straightdope.com/t/do-all-elements-have-a-half-life/347316/8 "2006-03-07T00:08:43Z")
> [@Q.E.D.](#):
>
> Sheesh, nice typing above, **Q.E.D.**! :smack:
>
> Also, there’s some evidence that protons can decay with a hugely long half-life, but I believe that only applies to free protons, not those bound inside atomic nuclei, yes?
I honestly don’t know. I knew that at one point there was some interest in trying to detect proton decay, and that the pools set up for that purpose were some of the best means to detect supernovae, but that exhausts my knowledge on the issue.
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### Author:  [@Anne\_Neville](https://boards.straightdope.com/u/Anne_Neville)
#### Post date: [March 7, 2006, 12:26am UTC](https://boards.straightdope.com/t/do-all-elements-have-a-half-life/347316/9 "2006-03-07T00:26:27Z")
> [@OtakuLoki](#):
>
> I honestly don’t know. I knew that at one point there was some interest in trying to detect proton decay, and that the pools set up for that purpose were some of the best means to detect supernovae, but that exhausts my knowledge on the issue.
You’re thinking of [Super-Kamiokande](http://www.ps.uci.edu/~superk/sk-info.html#pdk), which could detect proton decay. It is also used for detecting neutrinos, which come from supernovae as well as from the Sun. The supernovae aren’t necessarily detected by the neutrino detectors, but it is another way to study supernovae.
Experiments at Super-Kamiokande, by the way, have set 10[sup]35[/sup] years as the lower bound for the proton’s half-life. They haven’t ruled out that protons really are stable and don’t decay.
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### Author:  [@OtakuLoki](https://boards.straightdope.com/u/OtakuLoki)
#### Post date: [March 7, 2006, 12:32am UTC](https://boards.straightdope.com/t/do-all-elements-have-a-half-life/347316/10 "2006-03-07T00:32:17Z")
Thanks, **Anne Neville**.
I seem to recall, too, that neutrino pulses from supernovae could often arrive at Earth well ahead of the visible light signal, because of the delay in how the energy of the explosion in the star’s interior was converted to light energy, which is why I was under the impression that the proton-decay experiments were also useful at detecting supernovae.
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### Author:  [@ftg](https://boards.straightdope.com/u/ftg)
#### Post date: [March 7, 2006, 1:24am UTC](https://boards.straightdope.com/t/do-all-elements-have-a-half-life/347316/11 "2006-03-07T01:24:10Z")
Neutrino pulses from a supernova were first detected from the [1987a supernova](http://en.wikipedia.org/wiki/SN_1987A).
End of hijack?
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### Author:  [@Polycarp](https://boards.straightdope.com/u/Polycarp)
#### Post date: [March 7, 2006, 2:28am UTC](https://boards.straightdope.com/t/do-all-elements-have-a-half-life/347316/12 "2006-03-07T02:28:21Z")
Actually, there is a flaw in the original question here. No **element** is stable or radioactive per se – every element has numerous isotopes, which are generally radioactive. But 81 elements have stable isotopes with no measurable decay rate, and most of these _as they occur in nature_ are made up of only the stable, non-radioactive isotopes. (Obviously, stable isotopes may actually be radioactive with extremely long half lives. One example is Indium, which is actually 95% composed of one isotope with a quintillion-year half-life.)
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### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [March 7, 2006, 2:40am UTC](https://boards.straightdope.com/t/do-all-elements-have-a-half-life/347316/13 "2006-03-07T02:40:43Z")
> [@Polycarp](#):
>
> Actually, there is a flaw in the original question here. No **element** is stable or radioactive per se – every element has numerous isotopes, which are generally radioactive.
I’m pretty sure I covered that, although it might have escaped you, what with all the typos. 😉
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### Author:  [@Lumpy](https://boards.straightdope.com/u/Lumpy)
#### Post date: [March 7, 2006, 2:59am UTC](https://boards.straightdope.com/t/do-all-elements-have-a-half-life/347316/14 "2006-03-07T02:59:48Z")
Leaving aside proton decay (which would be a property of the protons themselves, not any nucleus they happened to be in), and fantastically unlikely reactions like spontaneus fusion of elements at room temperature, then nucei lighter than iron are almost certainly completely stable. They’d **lose** energy if they emitted any particles. And even elements heavier than iron can be stable because any particles they could emit would cost more in binding energy than the reaction would yield. (Even heavy unstable alpha emitters don’t just emit multiple helium nuclei all at once and turn directly into lead). That said, the idea that anything heavier than two iron nuclei is theoretically unstable is intriguing though debatable.
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### Author:  [@Q.E.D](https://boards.straightdope.com/u/Q.E.D)
#### Post date: [March 7, 2006, 4:28am UTC](https://boards.straightdope.com/t/do-all-elements-have-a-half-life/347316/15 "2006-03-07T04:28:53Z")
> [@Lumpy](#):
>
> nucei lighter than iron are almost certainly completely stable.
You lost me here. Sure, the elements lighter than iron all have at least one stable isotope, but many (most?) of them have at least one unstable isotope, too. The unstable isotope of hydrogen is tritium, which is a beta emitter, decaying into helium-3.
> [@Lumpy](#):
>
> They’d **lose** energy if they emitted any particles.
Doesn’t anything which emits a particle lose energy? That wacky E=mc[sup]2[/sup] and all. Maybe I’m misunderstanding what your point is supposed to be here, so I’d appreciate some enlightenment here.
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### Author:  [@TJdude825](https://boards.straightdope.com/u/TJdude825)
#### Post date: [March 7, 2006, 6:30am UTC](https://boards.straightdope.com/t/do-all-elements-have-a-half-life/347316/16 "2006-03-07T06:30:10Z")
These isotopes with zillion-year half-lives are all well and good, but I seem to remember some that are just the opposite. Am I wrong in remembering that there are isotopes with half-lives of one or two jillionths of a second?
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### Author:  [@Pasta](https://boards.straightdope.com/u/Pasta)
#### Post date: [March 7, 2006, 6:54am UTC](https://boards.straightdope.com/t/do-all-elements-have-a-half-life/347316/17 "2006-03-07T06:54:29Z")
[The table of nuclides](http://atom.kaeri.re.kr/) gives the decay properties of all known isotopes.
Protons have never been observed to decay (leading to the lifetime limit noted by **Anne Neville**.)
**TJdude825** : Poke around the above table in the A\>200 region for some winners (such as protactinium-219 – half life: 53 nanoseconds.)
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### Author:  [@Malacandra](https://boards.straightdope.com/u/Malacandra)
#### Post date: [March 7, 2006, 9:51am UTC](https://boards.straightdope.com/t/do-all-elements-have-a-half-life/347316/18 "2006-03-07T09:51:34Z")
> [@Pasta](#):
>
> [The table of nuclides](http://atom.kaeri.re.kr/) gives the decay properties of all known isotopes.
>
> Protons have never been observed to decay (leading to the lifetime limit noted by **Anne Neville**.)
>
> **TJdude825** : Poke around the above table in the A\>200 region for some winners (such as protactinium-219 – half life: 53 nanoseconds.)
They said I was mad! Mad? I, who have successfully synthesised a whole kilogram of Pa-219…
Damn. :smack:
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### Author:  [@Anne\_Neville](https://boards.straightdope.com/u/Anne_Neville)
#### Post date: [March 7, 2006, 6:15pm UTC](https://boards.straightdope.com/t/do-all-elements-have-a-half-life/347316/19 "2006-03-07T18:15:18Z")
> [@Lumpy](#):
>
> nuclei lighter than iron are almost certainly completely stable.
Nope. That might be true if the curve of binding energy were strictly increasing from hydrogen-1 to iron-56, but [it’s not](http://www.physics.carleton.ca/~watson/LinR_course/Sun_and_Stars/gifs/Bindingenergypernucleon.gif).
> [@TJdude825](#):
>
> These isotopes with zillion-year half-lives are all well and good, but I seem to remember some that are just the opposite. Am I wrong in remembering that there are isotopes with half-lives of one or two jillionths of a second?
If there were such a number as a jillionth, there probably would be 😉
This leads to something that people get wrong about radioactivity. They talk about radioactive elements with long half-lives, and say things like “It will still be radioactive for X years” (where X is some large number). But, all else being equal, it’s radioactive elements with _short_ half-lives that you have to worry about more- they emit much more radiation at a time than an element with a long half-life.
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### Author:  [@chrisk](https://boards.straightdope.com/u/chrisk)
#### Post date: [March 7, 2006, 6:38pm UTC](https://boards.straightdope.com/t/do-all-elements-have-a-half-life/347316/20 "2006-03-07T18:38:12Z")
> [@Anne Neville](#):
>
> This leads to something that people get wrong about radioactivity. They talk about radioactive elements with long half-lives, and say things like “It will still be radioactive for X years” (where X is some large number). But, all else being equal, it’s radioactive elements with _short_ half-lives that you have to worry about more- they emit much more radiation at a time than an element with a long half-life.
Yeah. Although long halflives, to a certain extent, can be dangerous in a more subtle way… like radioactive ‘time bombs’ that appear to be fairly normal matter until they go off. (Okay, not quite like that, since the whole essence of a half-life is that radioactivity is decreasing over time, not increasing. But total exposure does increase over time, obviously.) Strontium 90 is a nasty one in this sense, with a half-life around 30 years, and being chemically similar enough to calcium that it can get deposited in human bones. :eek:
And then, there are the multiple-punch radioactive elements, with a slow original half-life and then decaying into another radioactive element with a much shorter half-life, into another radioactive element etcetera.
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