Do all elements decay? or just ones that are radioactive? Do they more basic elements like hydrogen, helium, and oxyogen decay? How about water?
Only radioactive elements undergo radioactive decay.
Also, water is not an element, it is a compound of hydrogen and oxygen.
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.
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.
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.
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?
Good point! :smack:
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, 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.
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.
Neutrino pulses from a supernova were first detected from the 1987a supernova.
End of hijack?
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.)
I’m pretty sure I covered that, although it might have escaped you, what with all the typos.
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.
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.
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.
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?
The table of nuclides 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:
Nope. That might be true if the curve of binding energy were strictly increasing from hydrogen-1 to iron-56, but it’s not.
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.
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.