[Physicist]

One of the things that was discovered is that the mass of any nucleus is always less than the sum of the individual particles (called nucleons) that make it up. The difference (residual) is due to the “Binding Energy” of the nucleus. This binding energy is directly related to the strength of the strong force. Note: This is why there is a release of energy when an atom is split. (nuclear fission).

"Binding energy" is a negative energy. If the mass of a nucleus were always less than any sum of its potential components, then it would always take energy to split a nucleus. This is true for any nucleus below iron. For nuclei above iron, the binding energy becomes less and less; the strong nuclear force creates stable minima in which very heavy nuclei can exist, but these are but local minima sitting high on the electromagnetic hill. A uranium nucleus is heavier than thorium plus helium.

Doc Smith, in the classic novel Triplanetary, made the error of taking binding energy to be a positive, exploitable energy. Accordingly, the aliens used iron as fuel for their starships, iron having the maximum binding energy...sucking it, if necessary, out of the hemoglobin of human beings! In reality, iron is the one nucleus that can't be used for fuel, but I'm glad I didn't know that as a 12-year-old just the same.

[FreeTheHostages]

In reality, iron is the one nucleus that can't be used for fuel, but I'm glad I didn't know that as a 12-year-old just the same.

LOL. Hmm, I distinctly recall based on an experience of mine as a 12-year old -- my coffee ice cream landed on a corroding iron railing of a bridge in a small Vermont town and I greedily tried to retrieve and consume it -- that iron (especially when it's oxidizing and getting all weirdly brown and just turning rusty-colored, disguising itself well in the ice cream) does NOT taste good. I convulsed immediately, never did swallow, and still can't the taste completely off my tongue.

OK, that was totally off track but there you are. Iron tastes bad. Or, to be scientifically precise, at least when you're 12 years old and you attempt to consume it in a partially oxidized form in combination with coffee ice cream.

[RadioAstronomer]

Binding energy" is a negative energy. If the mass of a nucleus were always less than any sum of its potential components, then it would always take energy to split a nucleus. This is true for any nucleus below iron. For nuclei above iron, the binding energy becomes less and less; the strong nuclear force creates stable minima in which very heavy nuclei can exist, but these are but local minima sitting high on the electromagnetic hill. A uranium nucleus is heavier than thorium plus helium.

One Of the interesting things about the curve of binding energy is the elements that are created in stellar processes:

The weak force is the force that induces beta decay via interaction with neutrinos. A star uses the weak force to “burn” (nuclear fusion). Three processes we observe are proton-to proton fusion, helium fusion, and the carbon cycle. Here is an example of proton-to-proton fusion, which is the process our own sun uses: (two protons fuse -> via neutrino interaction one of the protons transmutes to a neutron to form deuterium -> combines with another proton to form a helium nuclei -> two helium nuclei fuse releasing alpha particles and two protons). The weak force is also necessary for the formation of the elements above iron. Due to the curve of binding energy (iron has the most tightly bound nucleus), nuclear forces within a star cannot form any element above iron in the periodic table. So it is believed that all higher elements were formed in the vast energies of supernovae. In this explosion large fluxes of energetic neutrons are produced which produce the heavier elements by nuclei bombardment. This process could not take place without neutrino involvement and the weak force.