How did the creation of the universe depend on Beryllium-8?
During the first few minutes after the Big Bang, the temperature and density was dropping very rapidly by millions of degrees per second. We know that every element has its own threshold for 'fusion', but in the Big Bang, these elements had to be made systematically beginning with the lightest ones. The Big Bang seems to have had the required temperature and density ranges to produce the following elements:
Protons Neutrons Weight Half-life .............................................................. Hydrogen 1 0 1 stable Deuterium 1 1 2 stable Tritium 1 2 3 12.26 years Helium-3 2 1 3 stable Helium-4 2 2 4 stable Helium-5 2 3 5 10^-21 seconds Lithium-5 3 2 5 4 x 10^-22 seconds Helium-6 2 4 6 0.8 seconds Lithium-6 3 3 6 stable Lithium-7 3 4 7 stable Beryllium-7 4 3 7 53.6 days Lithium-8 3 5 8 0.86 seconds Beryllium-8 4 4 8 5 x 10^-14 seconds Beryllium-9 4 5 9 stable Boron-9 5 4 9 Decays instantly Beryllium-10 4 6 10 2.5 x 10^6 years Boron-10 5 5 10 stable Carbon-10 6 4 10 19.1 seconds Boron-11 5 6 11 stable ..............................................................................But the problem is that heavier elements and isotopes require greater temperatures and densities to form them because they have more and more protons to provide electrostatic resistance during the collision and fusion process. Also, many isotopes are not stable, and if their half-lives are SHORTER than the time between fusion collisions, the isotope will decay away before there is time for the next collision to use it to build the next heaviest element. Since the temperature and density of the universe was rapidly declining, there will exist a 'last element' produced in this race against time. That race seems to have ended with beryllium whose 4 protons put up quite a big fight against further thermonuclear fusion into still heavier elements. Also, there is a race against time for the half-lives of the particles. As you can see from the above table, there was a big bottleneck with helium-5, lithium-5 and helium- 6. The elements below an atomic weight of 5 were synthesized in large numbers so that today, helium-4 constitutes nearly 25 % of the composition of the universe. But the next few stable elements, lithium-6, lithium-7 and beryllium-9 had to go through several more bottlenecks to be synthesized. Calculations predict that compared to hydrogen, lithium-7 makes up about 8 x 10^-10 of the universe as a primordial element, beryllium-7 makes up 2 x 10^- 11, and beryllium-9 is 8 x 10^-15. Their abundances are so 'astronomically' small that they can hardly be detected.
If the helium-5 and lithium-5 and beryllium-8 half lives had been longer, then more of the heavier elements would have had time to form, but there would still have been other bottlenecks further up the ladder to surmount, and remember, the universe is continuing to cool and become less dense as it gets older, so the required conditions for creating these heavier elements would have existed for shorter and shorter times.
Copyright 1997 Dr. Sten Odenwald
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