A staple of many sci-fi scenarios is that aliens have advanced technology because of the properties of “ultraheavy” elements, i.e., those with an atomic number of 250 or whatever.
Is this even remotely plausible?
Would there be any way to predict the stability of elements with atomic numbers larger than those already discovered/created?
IANANP, but we have never been able to keep any of the artificial elements higher than about Am around for any real use (it’s used in smoke detectors.) Remember that any new artifical element will be radioactive for all isotopes, so the use would be limited by half-life and any radiation concerns.
As I understand it, eventually there are problems with the sheer size of the nucleus. Most every element created above Am is very short-lived, at least in the isotopes we have managed to create. Now, most of them are probably metals and 118 would probably be a gas. The problem is that they all undergo alpha-decay very quickly. Quite frankly, while I believe that we could probably make all the way up to 118, and maybe even further than that, I doubt that anything higher than about 96 will ever prove to be stable enough to do something with.
I remember some years ago reading how some hypothesized that eventually there would be a stable region where super heavy elements would be more usable…has that fallen out of favor?
“stable” meaning in the order of milliseconds, not hours.
I’m not really supposed to talk about this, since my paper’s being reviewed by several scientific journals and the Nobel committee, but since it does answer the OPs question, I’ll go ahead and post it.
I have discovered the heaviest, densest element possible. I call it, “Moronium” and it’s so dense that not even intelligent thought can escape. Indeed, if enough of it is brought together in one place, it reaches what I call idiotical mass and begins sucking all intelligent thought from everyone in a five mile radius. I’ve not been able to figure out if it’s a naturally occurring element or manmade, but then again, the health effects are so severe that one cannot study it closely for long periods of time without suffering permanent damage. I’ve yet to find any shielding which effective blocks eminations from this element.
Nope, nuclear physicists still talk about islands of stability. Ununquadium, which was first synthesized in 1999, lies in such an island. It’s remarkably stable for such a heavy element: the most stable isotope has a half-life of about 20 seconds.
Of course, this is a far cry from a Z = 250 element. So caveat lector.
Regarding industrial uses of artificial elements beyond Americium (atomic #95) -
Californium (#98) and curium (#96) seem to have some limited uses. From webelements:
Since the world production of smoke detectors only requires a few kg per year of americium, I imagine the amounts of the others produced for commercial use is even smaller.
Let’s bring in the astrophysicists.
Feel free to jump in and correct me on the following, because it has been many years since I had college chemistry and physics (on which I scored A.A.A.A.B.)
Stars are hydrogen, and by fusion, convert it to helium. (Are any other fusion reactions going on in stars?)
Heavier elements are created by nova/supernova explosions.
Are some of you assuming that all possible stable elements have been created by these natural processes?
Is it perhaps possible that more stable elements could be created in an “older” part of the universe, or locally in another couple billion years of star creation/supernova/star creation/supernova/etc.?
Flail away. I would really like to see more on this subject.
Iron is the heaviest element that results in a net energy gain when it is produced via fusion. That is, fusing iron atoms to produce heavier elements results in a net energy loss. Once a star begins creating iron, and only the larger ones do, it’s on its last legs.
Naturally-occuring elements heavier than iron, yes.
It seems to be a valid assumption, given that all manmade transuranic isotopes are unstable and invariably decay into a stable isotope that’s also naturally-occuring.
I don’t know. I don’t know if the strong force is strong enough to overcome the electrostatic neutron-neutron repulsion in any atom heavier than uranium.
Oh, we will. This is the SDMB, after all. 
Surely you must mean electrostatic proton-proton repulsion, as neutrons have no net electric charge.
I think Tuckerfan nailed it.
Given that we keep “discovering”/“engineering” heavier elements as our technology advances… It goes to stand that we’ll eventually make another heavier one… and out of the billion other intelligences out there… surely some alien race (probably Chinese) wlll trounce us.
And here I was, hoping that I’d get that statement wrong in an interesting way. 
The other elements below iron on the periodic table are naturally present in lesser quantities, and are produced in hot-star cores on approximately those quantities.
BTW, while iron-56 is at the precise bottom of the curve of binding energy, its sister isotopes and those of cobalt and nickel are so little distance above it as to be essentially metastable, in particular one isotope of nickel (58 IIRC as a top-of-head recall) that lies in what’s essentially a “crater above the valley floor” – that is, while it takes a net energy infusion to produce it from Fe56, it’s energy-positive with respect to virtually everything else, and once having been produced, it takes sufficient energy to cause it to change that it is essentially as stable as Fe56.
Elements above nickel, of course, can only be produced by a massive influx of energy per nucleus, and therefore almost certainly are the products of supernovae. In one intriguing case, the decline in effective radiance by half of one class of supernovae is identical in time to the half-life of an isotope of californium, a suggestive parallel.
The reason that lithium (and the other light elements) are on that list is that while they’re produced in large quantities during helium fusion in hotter-star cores, they’re not stable at the temperatures it takes to produce them, and quickly either break back down into helium or (in smaller quantities) are further fused to produce carbon, etc.; the one time when temperatures are sufficient to produce lithium yet drop quickly enough to prevent its breaking down again, is in an outer layer of the core of supernovae. This is a major contributing factor to the relative scarcity of lithium (and to a lesser extent beryllium and boron) compared to neighboring elements.
I am not a physicist, but if I recall from my courses the problem with heavier elements is the conflict between electromagnetism, which wants to push the nucleus apart, and the strong nuclear force, which wants to keep it together. Small nuclei are stable because the strong force is stronger than the electric repulsion. But the strong force is very short range, so protons on opposite sides of a large nucleus wont feel all the other protons strong force, but they will feel all the electric repulsion. This is why heavy nuclei have so many neutrons–they give more strong force without adding any electromagnetic force. However even extra neutrons are not enough to create stable trans-uranic elements.
“Try new improved plutonium! Now with extra neutrons for more stability!”
AFAIK, we haven’t discovered any new phenomena which would make super-heavy elements stable. They would still be subject to the same tug of war between the strong and electromagnetic force, with EM winning over large distances. (Large on the nuclear scale of course.) MikeS’s link makes me hestiate to say that, but even the phenomena his links describe only make heavy elements less unstable–they don’t give the sort of stability SF writers postulate.
Stable superheavy elements are just a sort of hand waving explanation SF writers use to come up with whatever Miracle Matter their stories require. There’s nothing wrong with that, if it keeps the story entertaining and you remember it’s only fiction. And, of course there may in fact be some unguessed at phenomena that makes superheavy elements stable. It’s not like nature hasn’t surprised us before. But, again AFAIK, we haven’t discoverd any evidence of any such phenomena so far.
I hope a passing physicist stops by to correct any errors in this post. Also, please forgive the anthropomorphic language. It’s early and I couldn’t think of a better way to express myself.
Your understanding is good as far as it goes, but nuclei are messy beasts at the best of times and so more complicated effects come into play that adjust the simple version. In particular, the argument about the strong force balancing electromagnetic repulsion is essentially a classical one. Take quantum mechanics into the picture and it changes a little.
Imagine a neutron sitting inside a large nucleus. What force does it feel on it? At this level of complexity we’ll ignore electromagnetism, so the only force it feels is the strong interactions from surrounding nucleons. These have to be added up to give the overall force on it. If it’s at the centre of the nucleus, then all these nucleons are pulling in different directions and tend to cancel out. If it’s midway to the surface, they’ll roughly cancel out, but nuclei get denser towards the middle, so on average there will be more neighbouring nucleons towards the centre than towards the outside. Net result, a force towards the centre. If it’s at the surface, then the force is obviously inwards, but falls off rapidly outside due to the short range nature of the strong interaction. Clearly, at least classically, we will expect the actual force on the neutron to depend on the exact positions of all the other nucleons, but we’re only thinking of the average here.
You can do something similar with a proton, though that’s obviously messier because electromagnetism.
Now draw an analogy: it’s all much as if our neutron (or proton) is sitting inside a potential well. A well created by its interactions with its fellows. Now calculating how a particle behaves inside a potential well is something we know how to apply quantum mechanics to. What happens? We get quantised energy levels and all the fun stuff we know from grinding through the hydrogen atom. Similar things happen within nuclei.
The result is the shell model of the nucleus, which won Goeppert-Mayer and Jensen a half-share of the 1963 Physics Nobel.
Now I should stick a caveat in here. Because nuclei are messy, the descriptions theorists use in practice are only approximate. The shell model’s a good example, in that it gives a wonderful picture of some nuclear phenomena, but a horrible account of others. The trick is always to have a feel for what’s the best available approximation to be using to look at the particular aspect you’re interested in. Thinking about nuclei thus often becomes a matter of jumping from one picture/model/approximation to another.
How does this relate to MikeS’s links? Let’s push the analogy with atomic physics a bit further. We know that, in that case, electrons around nuclei sit in shells. Furthermore, atoms that exactly fill their electron shells are particularly chemically stable: they’re the noble gases. In the shell model of nuclei, something similar happens. As you add nucleons to a nucleus and so work your way through the periodic table, the model corresponds to you adding these to nuclear shells. Completing a shell then gives a particularly stable nucleus. This gives rise to the notion of magic numbers. Nuclei with these specific numbers of neutrons and protons are unusually stable. This can be seen empirically amongst the known elements.
Where this is relevant to the ultra-heavy nuclei is that we will get the same effect in some of them: closed nuclear shells giving elements that are unusually long-lived compared to those of a similarish mass.
The crucial question then is how long-lived can these be? That nobody yet knows, though there have been plenty of attempts to estimate what the half-lives might be. Again because nuclei are messy, it’s not easy to extract solid numbers yet. Different approaches using different approximations give wildly different answers. And that’s to be expected, since we know that the answer should depend delicately on the assumptions used.
On the plus side, this does mean that it’s still impossible to utterly rule out the case that some nuclei in the next “island of stability” may have very long lifetimes and not just relatively long ones at that.
This page discusses the current situation in more detail, including something about how to search for any naturally-occuring superheavy nuclei.
It’s my understanding that most lithium in the present-day Universe, as well as a significant chunk of the helium and traces of beryllium, are primordial, that is to say, produced in the Big Bang before the time of stars. This is at least true of certain isotopes of these elements, and the ratios of abundances of them gives us a wealth of information on conditions in the very early Universe.
Oh man, this thread has blossomed into the kind of discussion that I love about this board. Keep it coming, I’m learning so much…
Seriously, Polycarp, how the hell do you manage to know so much about so many different things? It’s not freaking fair, I say!
Some thoughts:
If there is actual real stability in the high numbers then it should exist naturally.
A neutron star might be thought of as a stable single ‘atom’ with a really big atomic mass, and held together by gravity.
To create stable super heavy elements naturally it might require a piece of a neutron star, as opposed to a super nova, so might be many times rarer.
Thanks for your post and your link, bonzer. I appreciate the clarifications and corrections.
Man, I’m always learning something here!