# Why does the binding energy curve ever decrease?

So the way I understand binding energy is that if I have two nucleons and I let the come together, they’ll decrease their potential energy as they move closer and this will speed them up as they’re flying towards eachother. Therefore, binding energy is the energy that you must remove from the nucleons so that they stay together and don’t fly past eachother rather than a energy you put in to hold them together. But by that logic, wouldn’t adding nucleons always increase the binding energy then? For example, if I have nickel-62 and I want to add a nucelon to it, then as the nucleon and nickel atom move closer together with a certain kinetic energy, I have to remove that kinetic energy for them to stay together which would be the binding energy. Therefore, binding energy should continuously increase but the curve decreases at nickel-62, so is my understanding that binding energy is the amount of energy you take out wrong?

• The usual binding energy curve shows the mean binding energy per nucleon, not the total binding energy of the nucleus. – PM 2Ring Feb 13 at 1:57
• Trying to add a proton to a nucleus is harder than you seem to think... – Jon Custer Feb 13 at 3:35
• Related post by OP: physics.stackexchange.com/q/460457/2451 – Qmechanic Feb 13 at 7:07

## 1 Answer

A qualitative argument is : because there are two forces entering into the binding of individual nucleons into ensembles: the strong force (attractive), the electromagnetic (repulsive) and neutrons can act as a |"shield" for an electromagnetic repulsion, it is not strange that there exists a maximum in the curve.

In section 2.5 here a derivation using the liquid drop model is described. It is also in the wikipedia article .