In reply to Michel Jullian's message of Fri, 23 May 2008 01:42:01 +0200: Hi, [snip] >I am sure it can! What's your take on the reason why deuterons fuse more >easily than identically charged protons BTW? Jones proposed a reason that >didn't convince me, namely that the extra neutron does some screening. [snip] The reason I have seen elsewhere is that the extra neutron increases the nuclear binding force, which of course helps to pull the nuclei together (at short range). I think if you look at quantum calculations of the cross section of similar types of reactions, you will see that increased energy of the reaction usually results in a larger cross section (which is just a restatement of what I just said about the nuclear binding force).
(Note this is only true where apples are being compared with apples - you can only compare reactions that have the same energy disposal mechanisms, and also both reaction must either involve or not involve the weak force. E.g. the D-D reaction can be compared to the D-T reaction, but not to the P-P reaction. In the former case we see that the cross section of the D-T reaction is larger because the extra neutron results in a greater binding energy. Both D-D and D-T dispose of their energy through particle emission. You see the same thing when comparing the P-D reaction to the P-T reaction. Both lose energy through gamma emission, but the P-T reaction has a larger cross section because of the greater binding energy. BTW, it isn't clear from your question when you refer to protons whether you are referring to the P-P reaction or the P-D reaction. The former has an extremely low cross section because a weak force conversion reaction is required. IOW while a proton might more easily tunnel, it still has to undergo a weak force reaction while in the nucleus. P-D has a lower cross section than D-D because it can't dispose of the energy of the reaction through particle emission. It has to dump the energy through gamma-ray emission and this is thousands of times slower than particle emission, which in turn results in a much lower cross section. Or alternatively, you can think of such reactions as more likely to simply "fall apart" again ( a form of particle emission where there is no net energy release), than to emit a gamma ray. Regards, Robin van Spaandonk The shrub is a plant.
