How do they determine when an element first came into existence?

Every so often I read about a new element discovered in an accelerator, with a half-life of nth-seconds. It will take its place on the periodic table.

Did they just look and were surprised?
More basic question. Pick an element. I choose Lithium. I’m guessing it has a recognized coming-into-the-universe date. How do they derive that?


I expect you know already that the periodic table is organized by the elements’ properties, not the order of discovery or creation. New elements are added when they are detected - it’s not enough to say that an element exists, someone has to actually find some.

Up until around 1940 there were gaps in the table, and people went looking to fill them. Since then the gaps are all at the end - currently the highest is 118. Heavier elements are expected (perhaps much heavier still), but they won’t be added to the table until someone proves they exist. And since they don’t occur naturally on earth, that means someone has to figure out how to make them.

For non-radioactive elements, there’s no way to determine a date when a particular atom was formed. However, most elements were created inside the giant nuclear reactors we call stars, and we have a pretty good idea how long the Universe has been around, and therefore how long ago the first-generation stars burned to create the heavier elements.

But since the OP specifically mentioned lithium, that’s one of the few that’s primordial, and formed during Big Bang nucleosynthesis. Practically all of the hydrogen and lithium in the Universe, plus a big chunk of the helium and a bit of the beryllium, were formed in the Big Bang. Everything else was formed almost entirely in stars.

The teams that report discovering new elements aren’t “looking” for them in the usual sense. They are trying to create them by good old fashioned atom smashing: smashing particles together in the hopes that some of them stick. The properties of “unknown” elements can be deduced, to a good first approximation, by extrapolating from already known elements. This has been done for probably seventy-five years, though better and better detection devices. Remember the “bubble chamber,” a staple of popular science from decades ago? The tracks, the breakdown particles, or other signatures of an elements and its successors can be looked for after an experiment is run. When enough evidence of a new and heavier element is produce to satisfy the standards international bodies have set, the creators get credit for the “discovery,” which really means the creation of the new element.

That’s how the dates are set for elements not findable on earth. Those that are can be explained by theories and calculations. After the big bang, stars build up other elements. Large stars, the ones thought to be produced in the early universe, must explode (anything 8 times the sun’s mass or over does). Those explosions can create heavier elements and spread them throughout the universe, where they can get reused and accreted in planets.

We are stardust. Billion year-old carbon. Joni Mitchell got it right, to within an order of magnitude.

Hmmm, so there are no stellar nuclear reactions that leave lithium behind as an end product?

After just now finding this page (stellar nucleosynthesis), and reading the other pages linked to under “Key Reactions”, I guess the answer is no.

I’d be curious to know however, whether (1) there is no fusion reaction that yields lithium, or (2) there is one, but in the conditions where lithium could be produced, it’s quickly fused with something else (nearby hydrogen or helium) and so doesn’t last very long. Or (3), there’s something else going on I’m not thinking of.

I wouldn’t be so bold as to say that there’s absolutely no stellar reaction that could produce lithium, but if there is, the rates are low enough to be negligible. Most stellar reactions above the H -> He ones proceed via multiples of helium.

And actually, to be fair, some elements come primarily from various decays of things made in stars or supernovae, not directly from the stars themselves.

Thanks, and now I know the word/concept nucleosynthesis, and I’ve read some of the pieces to the limit of my ability. I see that Lithium is mentioned here and there as a border case.
Now, I picked Lithium at random. All the other star-produced elements: besides saying they come from a star, can one say, OK, from star-type x, now appearing for the very first time, the new element y, created at a particular (rounded) time?

I just wanted to chime in to recommend a book I really enjoyed, The Disappearing Spoon. It covers a lot of history, as well as some very interesting scientific facts about the elements and the periodic table as we know it today.

I particularly found the trail to discovery of element 43, Technetium to be pretty fascinating, considering its elusive nature in nature. The book covers it in good detail.

Carry on… :wink:

beowulff has already given a solid (negative) answer, and I neglected to acknowledge that. Apol.

Based on memories of asking “the lithium question” and how it was answered:

It seems counterintuitive to think of the core of a red giant star as a quiet, peaceful place, but it is a place where steady gradualistic processes predominate. Protium fuses into deuterium, deuterium into helium-4, three helium-4 into carbon-12, and so on.

A reaction must be ‘arithmetically’ possible: e.g., nuclei with X protons and Y neutrons fuse with ones with Z protons and W neutrons to form an unstable nucleus of X+Z protons and Y+W neutrons, which then gives off an alpha particle and becomes a stable nucleus of element X+Z-2…)

There is also a threshold energy for its creation, a minimum temperature and pressure below which the reaction will not occur. And when you’ve reached that threshold, there may well be other reactions that “it’s hot and dense enough for” that will happen alongside it. Some of these are endothermic.

Lithium has two isotopes which are ‘stable’ – i.e., non-decaying at temperatures and pressures below those of stellar cores. Helium-3 is also stable; tritium, hydrogen-3, has an 11-year half-life, short on the geologic time scale but quite long compared to the average random non-stable nuclide, whose half-life may be measured in microseconds – such as beryllium-8.

What unites these nuclides, and makes them relatively uncommon in nature, is that the temperature and pressure needed to create them in an “isotope nursery” stellar core is higher than the temperature and pressure at which they tend to break down into smaller nuclides. They can be produced in trace quantities below that – all the tritium on earth, for example, comes from reactions in the upper atmosphere. And of course once produced, they exhibit their characteristic stability in terms of nuclear decay. But for the ‘industrial level’ production in stellar cores, fuggidaboudit! Not happening! Temperatures conducive to producing lithium nuclides are even more conducive to breaking down litium nuclides as soon as they’re produced.

The catastrophic conditions inside a supernova, and even more so within the Big Bang, are different. Particles and nuclides are slammed together willy-nilly, with no time for reaction or decay before they are again slammed into something else, and eventually expelled in the enormous explosions. The results include a small ‘production run’ of the so-called ‘forbidden nuclides’. the ones that in gradualistic stellar-core conditions will break down as soon as formed.

Hence the confident assertion about lithium.

Sounds like the stars need to switch medications.

And maybe get out a bit more.

Well, since a monopole has never been observed, they’re all obviously bipolar, I’ll give you that. :slight_smile:

One point hinted at by Polycarpe, but not made explicit is that all elements above iron in the periodic table are made only in supernova explosions. The reason is that the creation of elements iron and below releases elements–causes the stars to shine. Above iron, it requires energy and that happens only in a supernova. That is why fusion of elements below iron and fission of elements above iron both release energy. One thing I am not especially clear on is why elements above iron can be stable.

The same reason anything can be stable: There’s an energy barrier to the reaction. You’d have to put in a lot of energy to get the atom to fiss. If you actually put in that energy, you’d get even more energy out in the process, but you still need to put in the initial energy.