# How is binding energy actually measured?

How, exactly does one measure binding energy?

Or, assuming binding energy is calculated from mass defect and $E = mc^{2}$, then, how is mass defect measured?

I know one can be calculated from the other (with eternal gratitude to my personal hero Einstein), but I'm curious how the first to be discovered was accurately quantified.

You don't measure binding energy directly. You measure masses for stable nuclides (and certainly for long-lived radionuclides, like $\rm^{40}K$ or $\rm^{14}C$, and possibly for long-lived isomers). You measure energies absorbed or released in reaction between nuclides where you know the mass. And from laddering these energies and masses all the way up from the nucleon to the actinides, you come up with a self-consistent picture of all the binding energies.
• Yes, I mentioned mass in my original question. Assuming the mass is measured (and energy is calculated), then how can one accurately measure the mass? If we're talking about the decay of radionuclides, then I suppose the total energy released in a decay can give clues to the masses of the decay products. But what about e.g. everyone's favorite most-stable nucleus, $^{56}$Fe? How did scientists determine its mass defect and/or binding energy to begin with? – pr1268 Aug 17 '16 at 4:48