- #36
mfb
Mentor
- 37,194
- 14,034
D+D is extremely rare. For every deuterium nucleus there are ~1017 protons around for p+D -> He-3 + photon. It does happen, so some tritium is produced. But then you have the same problem again: Deuterium is extremely rare. p+T -> He-4 + photon is much more likely than D+T -> He-4 + n. I guess a few neutrons are produced via this reaction path, but the total number must be really small.phyzguy said:The proton-proton cycle fuses protons to deuterium. D + D fuses to He3 + n or T + p with equal probability, and of course D + T gives He3 + n. So, given the size of the sun, many free neutrons are produced.
You don't have to start with hydrogen. The Sun contains all long-living isotopes already from its formation, for most elements you just have to add one more neutron and wait for a decay, or just wait for a decay.Vanadium 50 said:That's not as big a number as it looks. Uranium requires 237 nucleon additions. What does that mean for the probability of each nucleus to glom on another nucleon? Is it 0.1%? 1%? 10%? No - it has to be 71%, otherwise you don't get all the way to uranium.
The fraction of induced fission of U-235 should be tiny, but there is spontaneous fission. I said this many posts ago already.Vanadium 50 said:That said, I believe every (natural) element is present in the sun, but for another reason: uranium fission. The tiny bit of primordial U-235 in the sun is exposed to neutrons and will fission.
If the Sun would have started with hydrogen exclusively it wouldn't contain uranium by now. Probably not even iron.DaTario said:but in order to be complete, if those heavy elements were not present, would the natural ascending (starting basically from H) processes of nucleosynthesis provide all the elements?