Friday, October 28, 2016

[qerzxorn] All the superheavy elements

If I understand correctly, the intense neutron flux inside a supernova will produce, via the r-process, all the superheavy elements, not just the ones typically labeled "naturally occurring" up to uranium or so.  Those beyond uranium do get produced, but decay quick enough that there is none left by the time the supernova remnant has recongealed to become (say) planet Earth.  The supernova also produces all the superheavy elements that have not even been discovered yet, so it's not the case that when scientists create a new element on Earth that it might be the first time that element has ever existed in the universe.  In particular, because of the high neutron flux, a supernova produces the neutron rich isotopes of the superheavy elements, which tend to be more stable than the ones produced by fusion of heavy nuclei on earth.  If a nucleus is unstable because it has too many neutrons, it will beta decay until the balance is just right.

If there are any more stable, or long lived, elements, a supernova would have produced them.  This means the hypothesized "island of stability" cannot really be that stable.  But this is at odds with some scientists predicting that the island of stability might contain elements with half lives of a billion years.  Are there isotopes with a nice ratio of protons and neutrons which cannot be reached by the r-process and beta decay?

Of course, there is an upper limit to the r-process, where perhaps cluster decay or spontaneous fission occur before the next neutron can reach the nucleus.

For the core part of the supernova undergoing gravitational collapse into a neutron star, the neutron flux could be even higher, and even heavier elements might very briefly form (still bound by the strong force).  Later, a neutron star itself might be considered a giant nucleus, albeit bound by the gravitational force not strong force.  (Tangentially, "nuclear pasta")

Design a spacecraft, or some other method, to capture and confirm heavy elements produced soon after a supernova.  Maybe go in a few minutes or a day after the event.  This will be pretty difficult: maybe a shield the size of a planet accelerated to relativistic speeds toward the Wolf-Rayet star or white dwarf, having guessed when the supernova will go off, or triggering it, so that the craft arrives at just the right moment.

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