I read that the SNF accounts for 99.9% of the mass of an atom.

So if 4 hydrogen atoms become 1 helium atom during nuclear fusion does that change the proportion of SNF as we have 4 SNFs becoming 1 SNF and 12 particles becoming 6 particles. Is it now 99.8% or something?

Thanks. (I'm just a curious layman, this question may make no sense :))

  • $\begingroup$ Please note that the Strong Nuclear Force ( your SNF in the question I suppose), as a force is not a conserved quantity.. Energy and momentum are, but a force is defined in physics in different units, massmeter/(secondsecond) so are not comparable quantities.that can be compared in interactions. $\endgroup$
    – anna v
    Mar 22, 2020 at 12:40

1 Answer 1


If the amount of mass due to strong interactions changed when four hydrogen atoms went through the chain of reactions necessary to form a helium atom, then the mass of four hydrogen atoms would be different from the mass of a helium atom. So let's see if this is the case.

Wikipedia tells us that the mass of a helium atom is 4.002602 atomic mass units. The mass of a hydrogen atom is 1.00782504 amu, so four hydrogen atoms is 4.03130016 amu, and we find that the masses are indeed different.

This is of course why nuclear fusion produces energy. When four hydrogen atoms combine to form a helium atom the mass decreases by about 0.029 amu. That mass is converted to energy and emitted as the kinetic energy of the reaction products.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.