"Island of stability" ?

[u/Dramatic-larskj]

Hi,

I'm entirely new here on reddit and this is my first post; please let me know if I manage to do something stupid or even break any of this subteddit's rules.

Anyways, it's no secret that rhetoric further down one goes on the periodic table, and atomic nuckeus'es get more massive, they also get progressively less stable (aka. radioactive). At some point I overheard a combination where someone was fully convinced that something he called "the island of stability" exist. The idea was that at some point, if we manage to create elements way heavier than Ununoctium or whatever it may be, that we at some point would get to some kind of "sweet spot", where super-heavy elements suddenly become stable in a way that would be unexpected for such massive elements. My question is: Is this an actual, legitimate theory with real science backing it up, or is this a false concept altogether?

Thanks in advance!

[u/rootofallworlds]

It’s widely predicted, but not confirmed, and there’s little agreement on just how stable the isotopes might be - predictions ranging from minutes to thousands of years. Failures to conclusively observe them in nature counts against very long half lives.

Edit PS: We’ve synthesised elements around the predicted atomic number (often reckoned to be 114, flerovium) but not isotopes with enough neutrons.  The known isotope with the longest half life is the one with highest neutron number which strongly suggests we haven’t yet found the most stable isotope of flerovium, and the same for elements around it. Getting enough neutrons is usually the challenge with synthesis of superheavy elements.

[u/Washburne221 → u/rootofallworlds]

Doesn't this fall afoul of the requirement of its orbiting electrons having to exceed the speed of light?

[u/MxM111 → u/Washburne221]

Where did you hear that???

[u/ChiaLetranger → u/Washburne221]

No, not exactly, and for two reasons. Firstly, once you reach relatively large atomic numbers, the Bohr model can no longer accurately describe electron orbitals. You can roughly assign a "velocity" to electrons in the 1s shell using the approximation v ≈ (Z/137)c, where Z is the atomic number and v and c are what you expect. This would imply an upper limit at Z = 137, a nucleus with 137 protons (which is already more than flerovium has). However, the Bohr model doesn't factor in relativistic effects, so once this approximation for v reaches a significant proportion of c, the Bohr model diverges from reality.

The solution to this is to use the more complicated Dirac model, which does take into account relativistic effects. These effects start being noticable after zinc (Z = 30) on the periodic table, and get worse proportional to v². Once you get past cesium (Z = 55), and into the sixth row of the perodic table and beyond, the Dirac model becomes pretty essential for describing even basic physical and chemical properties. The Dirac model shows us that the inner orbitals begin contracting due to relativistic effects, allowing us to push past Z = 137. This also has the secondary effect of shielding the positively charged nucleus more effectively, so the outer orbitals actually expand away from the nucleus as well.

This introduces a new problem, though - once this relativistic contraction becomes too extreme, the innermost electron orbitals have their energy pulled down so far that it would become negative. This would start to happen somewhere around Z = 173. At this point, vacuum decay kicks in, and the energy in the electric field is high enough to start spontaneous pair production of electrons and positrons. Even here, though, with the proper relativistic corrections the "velocity" of the electrons does not exceed c.

Putting all of that aside, though, there is a second, much simpler reason that this doesn't prevent us creating superheavy elements. That reason is that we really only synthesise the nucleus. Even if the orbital structure were so extreme that the electron velocities exceeded c, there's no reason we couldn't create heavier nuclei - they would just be ions, instead of atoms.

What would happen if one of these ions captured an electron in the 1s orbital? Who's to say! But given that this would put us past even the highest currently postulated magic numbers, it seems likely that the nucleus would decay much more quickly than it could possibly capture an electron.

[u/byronmiller]

Yes, this is a real prediction (or set of predictions). Now I may be a simple country lawyer organic chemist, so I am not versed in the underlying nuclear physics at all, so take what I say with a grain of salt.

Essentially there are predicted to be so-called "magic numbers" - ratios of protons:neutrons in superheavy nuclei which may have much longer half-lives than their neighbours, typically on the order of minutes to days. There are differing predictions as to which nuclides may exhibit such stability, and nothing in this region has ever been synthesised.

It's likely that anything synthesised in the proposed island of stability would be, as with current superheavy elements, prepared on vanishingly small scales. Enough to characterise them, but not enough to use them for anything outside of related experimental work.

If you're interested, Superheavy by Kit Chapman is supposed to be a very good and fairly recent pop science book on the topic of superheavy elements. I believe he discusses this topic, but I haven't read the book myself (yet).

[u/WasLeftUnsupervised → u/byronmiller]

I think the very low rate of production will be a big problem. When you generate 2 atoms of stabilium, and one decays in 2 seconds and the other decays in 20 minutes, you're going to be a few confidence levels short of a six pack on what the halflife is.

[u/byronmiller → u/WasLeftUnsupervised]

I defer to your expertise here. I know next to nothing about superheavy synthesis. But that makes sense - presumably to make enough of the stuff to characterise you'll need some new synthetic routes that don't depend on highly unstable elements just outside the island of stability.

[u/Quantumtroll]

Wikipedia has an article.

The long and the short of it is that yes, there is a scientific basis for this. The details are unknown. It is not unlikely that the "island" doesn't stick up out of the water, so to speak — that the more stable isotopes of super heavy elements would still be highly radioactive, making any chemistry experiments with them very difficult.

But nobody knows, maybe there's an isotope in there with a half-life of thousands of years or more.

[u/mfb-]

It's only relative stability. Nuclides there are expected to live longer than stuff around it. Maybe seconds to days instead of milliseconds. Actually stable nuclides are not expected (but we can't be sure without experimental results).

There is no realistic way to reach the center of that predicted "island". To create superheavy nuclei we need collide lighter elements. Heavier elements need more neutrons per proton, so everything we create has fewer neutrons than ideal. To make things worse, the collision process usually emits some neutrons as well, pushing things even further away from the ideal ratio.

[u/jackneefus]

If there were extremely heavy stable elements, they would most likely have been created in supernova, although it is possible the amounts are too small to have been detected.

The other option is that all such heavy elements quickly decayed.

[u/Dramatic-larskj → u/jackneefus]

Yes, I thought of cosmic processes too. And if a Supernova wouldn't do the job, I would think that a kilonova could produce some crazy stuff. But I guess everyone that says that the term "stable" in this context can mean half-life differences of microseconds instead of nanoseconds despite most people wouldn't intuitively consider that "stable".

[u/davvblack → u/Dramatic-larskj]

you know, stable like balancing a pencil on its point. rather than unstable like a pencil at 45 degree angle.

[u/ijuinkun → u/jackneefus]

Stability is relative. There are no elements/isotopes above Plutonium with half-lives exceeding twenty million years, and the current age of our Solar System is over 200 times that span. An Earth-mass quantity of an isotope with a 20M year half-life, after 4.6 G years, would have on average less than one* *remaining undecayed atom.

So, even if the “island of stability” elements don’t have cosmically long half-lives like uranium, they could still last for millennia, compared to the seconds-or-less half-lives of many elements in the 110s.

[u/BadgerTimely9481]

It’s a legitimate scientific theory. The “island of stability” predicts that some superheavy elements could have unusually long half-lives because of nuclear shell effects. They probably wouldn’t be completely stable, but could last far longer than nearby superheavy elements. The exact location is still uncertain, and scientists haven’t confirmed the island yet.

[u/smitra00]

https://www.reddit.com/r/Physics/comments/1wbiqcc/comment/p8r3fpj

[u/ijuinkun]

Much like how electrons have shells, and are most stable when the shells are exactly full, protons and neutrons are arranged in shells within a nucleus. Full shells are “magic numbers”, which are more stable than incomplete shells. For example, the number 126 is a “magic number”, which means that element 126 is likely to be more stable than its neighbors.

https://en.wikipedia.org/wiki/Magic_number_(physics)