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0 pointsnknezek10y ago0 comments

Yes, there is a reason. We've thoroughly explored the periodic table through our studies of nuclear processes (lots of government funding for anything nuclear weapons related). It turns out you can create a ton of elements we don't see in nature, but almost none of them are stable: you smash atoms together to make a new one, but the new one flys apart after a <second (and that's actually a long lifetime for these atoms, many have lifetimes of nanoseconds). There is a potential "island of stability" around element 120-130, but even there lifetimes are predicted to be less than a minute.

In addition to the stability argument, there are also energy requirements. It turns out fusion (stars) only gives energy up to iron, then it requires energy to make bigger atoms. In other words, you get energy back out when you split big atoms (I.e. nuclear reactors). In nature, all elements past iron are created only in the spectacular energies of supernovas, which occur in less than a second.

Basically, we have a really good grasp on the elements that can exist. We're only missing the details on a few things that occur on nanosecond and less timescales.

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phkahler10y ago

>> In addition to the stability argument, there are also energy requirements. It turns out fusion (stars) only gives energy up to iron, then it requires energy to make bigger atoms.

That's actually a common misunderstanding. If you fuse hydrogen (or even lithium) with iron, you can get a higher numbered element and some excess energy. See the chart on this page:

https://en.wikipedia.org/wiki/Nuclear_binding_energy

While iron is at the top of the curve, that just means you won't see iron-iron fusion. There really is no reason the lighter (common) elements can't fuse with the heavier elements.

This is also the idea the LENR (low energy nuclear reaction, formerly known as cold-fusion) guys are considering. If you fuse Hydrogen with Nickel62 to produce Coppper63 you could get some energy out. Notice that Nickel is already heavier than Iron. Some claim to have seen this copper production in hydrogen-nickel cells. The claims are not really relevant - the math supports it as a possibility. Weather it can happen on earth or in a star is open for debate. One key question is how the excess energy would get out as heat, and there are ideas about that.

I for one find it amusing that people don't think something like this is where all the naturally existing heavy elements came from.

scentoni10y ago

Wrong, it really does mean that it takes energy input to fuse iron and hydrogen. Naturally existing heavy elements are the result of supernovas, where a percentage of the energy of the dying star is converted to fusing elements beyond iron.

smaddox10y ago

Indeed. Oblig. hyperphysics: http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin.htm...

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