What is the Atomic Weight 5 Barrier?

Question

According to Evolutionary Physics, at the Big Bang elemental particles were blasted out. Soon hydrogen was formed with atomic weights of 1,2, and 3. Then isotopes of hyrogen formed helium with atomic weight 4 through fusion. Then Helium was bombarded with isotopes of hydrogen and produced lithium with atomic weights of 6,7,8. And so on and so on... Until all the elements were formed.

My problem is that Helium (AW-4) is so stable that nothing can fuse with it to form lithium. In fact the absence of an isotope of helium at atomic weight 5, accents the fact. If this is the case, how did we get the other 100 elements?

Answer 1

Stellar Fusion. Stellar Fusion can make elements up to Iron. After that they can't fuse anything more heavy. In really big stars, this limit causes the star to collapse, rebound, and explode, and it is thought that this explosion is powerful enough to fuse the other heavier elements.

Lately though, it seems that Supernovae are no longer enough, and there are physicists looking for other methods of fusion because stellar models predict that supernovae might not produce enough elements to explain the current observed amount of heavy elements out there....

So I guess it's still up in the air.

Answer 2

While some elements are formed in stars by one-step-at-a-time proton and neutron capture processes, the major energy-producing fusion processes after the proton-proton reaction that fuses hydrogen into helium involve reactions between more complex nuclei.

For example, after a star has used up the available hydrogen, it starts fusing helium-4 nuclei together three at a time to form carbon, in what is called the triple alpha process. Two He-4's make beryllium-8, but that is unstable.

The fact that some elements are more readily produced than others explains why some elements are scarcer than others. Thus, lithium, beryllium, and boron are less common than a number of heavier elements.

Answer 3

5Li is scarce because its binding energy is so much lower than that of 4He. When 5Li forms, it rapidly (half life 10^-22 sec) emits a proton for form 4He.