Extinct elements

[u/R6NOTCSK]

Would it be some radioactive elements just decayed over millions of years ago and now we don't know their existence (idk anything abt radioactive things , it's just a random question popped out in my head)

[u/CrustalTrudger]

Wikipedia article on extinct radionuclides provides some context.

[u/Dawg_in_NWA]

There are several extinct nucleides that we know of and that we use for research.

[u/ExtonGuy]

Elements are numbered by their number of protons, 1, 2, … 118. Each element can also have various isotopes, with zero to 176 neutrons, depending on the element. If there are any element past #118, they very likely are radioactive and last for only a few microseconds, not millions of years.

There is some thought that maybe we could make elements past #118, but nobody has been able so far.

[u/Naive_Age_566]

extinct is the wrong term. if something is extinct, it meand, that it existed some day but not anymore - and can not be brought back.

we know of 118 different elements. at least in principle, we can produce any one of them in a lab (only in very tiny amounts though). and you could not differ between a "natural" element and an artifical created.

we know of no process, that could naturally produce elements with a higher proton number than 118. and even is such a process would exists - such elements would only last for a tiny fraction of a second.

an element that comes closest to something you could vaguelly describe as "extinct" is technetium. this element is so highly radioactive that at any given point in time, there is only a few milligrams of this element on earth - exclusively byproducts of decay chains. its an element, that was first predicted because of that "hole" in the periodic table - a point, where an element should have been but none was ever found. it only has an proton number of 43 (silver has 47 and gold has 79) - but it can only be produces artificially.

[u/forams__galorams → u/Naive_Age_566]

extinct is the wrong term

Maybe for whole elements — as you correctly describe with the possible exception of technetium — but OP is clearly talking about specific nuclides/isotopes, for which ‘extinct’ is a valid and widely used term.

Extinct nuclides are used as tracers in medical physics and environmental studies. The specifically unique decay products of extinct nuclides are used to infer quantities of the progenitor nuclide in geochemistry/cosmochemistry studies, eg. the heat production of the early Earth is based in part upon quantities of Al²⁶ decay products that are stable enough to still be around. Or in environmental studies to monitor the rate and flow of water through some reservoir; or in medical studies to monitor the flow of something through the body, etc.

[u/Frangifer]

A 'tangential' answer to your question is that artificial transuranic elements tend to be isotopes of them that are very neutron deficient ... because the curve of ratio N/Z (where N is the number of neutrons & Z curves up with increasing atomic № Z is the number of protons) versus Z (and with fairly rapidly increasing curvature as Z is towards the upper end of its range), & the isotopes we have are made by impinging nuclei of lower Z together, which means that their N is given by a linear extrapolation of the curve lower down. This means that those of optimum N/Z ratio are not accessible: they can only be made by an r process of an intensity we can't even approach terrestrially ¶ , but which would be attained-to in a supernova.

¶ ... or maybe in the very early fireball of a nuclear bomb it's approached very briefly. Infact ... I recall that einsteinium was first found in nuclear bomb residue. I wonder which isotope it was?

🤔

Or put it this way: the half-lives of the isotopes of the transuranic elements we do have are a representation much-on-the-low-side of the half-lives those elements could have .

I don't know, though, what implications this would have for the presence of such elements in the proto-Solar-System nebula, or even on the very early Earth. It would require there to be some isotope of some transuranic element (probably one not too-far up, as then the half-life would be extremely short even in the case of isotopes having close-to-optimum N/Z) the most stable isotope of which has a half-life of maybe a somewhere in the region of a hundred million years, or a few hundred million years (or @least a few tens of million years), and which, for the reasons spelt-out above, is inaccessible by-means of particle accelerator synthesis techniques ... & I don't know whether any fit that requirement. Just maybe there was some isotope of curium or berkelium or californium , or something, that was very briefly present in small quantities on the very early Earth.

But maybe not even that: that problem with the isotopes the way we make them being neutron-deficient becomes increasingly acute for the higher-Z ones (eg a pretty decent № of isotopes of curium berkelium & californium are obtained), & their half-lives - even those of close-to-optimum N/Z - would be too short to be present on the early Earth ... so it may well be that there just was not really any 'thing' of transuranic elements being present on the early Earth.

... with the exception of plutonium-244 (half-life about 80million year) : we know there was a fair bit of that. Infact, there should be a truly miniscule amount of primordial plutonium-244 even now . ^§

It does mean, though, that there's probably a fair-bit of transuranic element content in the cloud immediately upon the occurence of a supernova. But they never get to exist other-than as thinly-dispersed in Space @ very great distance from anyone.

 

§ The Earth, @ 4½billion year old, is about 57 plutonium-244 half-lives old ... so the № of atoms will be reduced from its original № by a factor of about 2⁵⁷ ≈ 10¹⁷ ... so there should be a fairly decent amount left, actually.

... bearing-in-mind that a ㎏ of nickel is about 10²⁵ atoms thereof. ... so a ㎏ of plutonium-244 about ¼×10²⁵ atoms thereof.

[u/Simon_Drake]

Sortof.

Our sun is only big enough to fuse hydrogen into helium. Some larger stars can fuse helium into carbon, oxygen etc. but only the first couple of rows of the periodic table. For elements larger than iron they can only be created by supernovae and similar energetic events. So any gold, lead or mercury on Earth came from a supernova billions of years ago.

You will sometimes see it quoted that Uranium is the largest naturally occurring element on Earth which is mostly true. It's the largest element that we can mine out of the ground just like you mine tin or copper or gold. There are traces of the next largest element, Neptunium, but that's generated in the ground from radioactive Uranium decaying and transmuting into Neptunium. The next largest element is Plutonium and there ARE incredibly rare traces of Plutonium in the Earth's crust and this Plutonium is left over from that supernova that created all the gold and other heavy elements.

So technically there used to be more Plutonium in the Earth's crust and almost all of it has decayed away so that it's essentially all gone. BUT we can make new plutonium and the last ~30 elements on the periodic table by slamming smaller elements together or bombarding them with neutrons or alpha particles. So although the plutonium has basically all gone now, it's not gone forever like an archeological relic being eroded into dust.