Chemistry · Chapter 21

Inside the Nucleus

Dial in a proton count and a neutron count. The plot shows you whether that nuclide is one of the 251 stable ones or whether it has to decay, and the curve below shows how tightly its nucleons are held.

The band of stability neutrons up, protons across

The chosen nuclide marked on a plot of neutrons against protons

Binding energy per nucleon peak sits near iron-56

Binding energy per nucleon against mass number

Measured values. The climb on the left is why fusion pays. The slow fall on the right is why fission pays.

Your nuclide

Fe-56 stable
Mass number A = Z + N: 56
Protons Z: 26   Neutrons N: 30
Neutron to proton ratio: 1.15
Centre of the band at this Z: N = 30.4

What it does next

Prediction
Stable
Iron-56 sits inside the band, so it has no reason to change.

How tightly it is held

8.79MeV per nucleon
Total binding energy: 492 MeV
Mass defect: 0.5283 u
Share of the iron-56 peak: 100.0%

Mass defect comes straight from the binding energy, since 931.5 MeV is worth 1 u.

Jump to a real nuclide

Each small dot on the plot is a real stable nuclide. The shaded strip is a smooth sweep through those dots.