-----Original Message----- From: [email protected]
>Actually The neutron has mass slightly larger than that of a proton: >939.565378 MeV compared to 938.272046 MeV. Consequently, a deuteron has >slightly more mass than a diproton. >That is one of the many reasons why the reaction on the Sun, the one that >results in a deuteron is extraordinarily rare. It is basically endothermic. The mass of two protons is 2.014552933 amu. The mass of a deuteron is 2.01355362 amu. RVS: Note that the deuteron is actually lighter than the two protons. IOW this reaction is exothermic. Not exactly true, Robin. Once again - the deuteron does NOT form directly from two protons! Never. There is a required step which you are leaving out, where outside energy is brought in. The deuteron forms only from a diproton, which itself has formed from two protons PLUS added mass from outside the reactants. If that mass has not been added, which is the vast majority of the time, there is no reaction. IOW without added mass-energy which is brought in above the rest mass of the reactants, the reaction is endothermic. With the added mass the reaction appears exothermic, but that is due to added mass-energy from outside the reactants. Semantics allows either depiction - exothermic or endothermic, depending on whether one is looking at protons or diprotons. Since you were looking at protons, the reaction is endothermic based on their rest mass. This is similar to the situation with an accelerator - where a beam of atoms forms a new element which has an unfavorable energy balance - but the beam momentum adds the necessary mass-energy to make it happen. Protons in the sun can be accelerated locally to high energies. Jones
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