Nuclear Physics – Binding in the Nucleus Inside an atomic nucleus, protons and neutrons are held together predominantly by which interaction?

Introduction / Context:
Nuclear stability arises from a strong, short-range attraction that overcomes the electrostatic repulsion between protons. This question asks you to identify the nature of that binding interaction in standard textbook language.

Given Data / Assumptions:

• Nucleons = protons + neutrons.
• Protons repel via Coulomb force, yet nuclei are bound.
• The binding force must be much stronger at femtometre scales but short-ranged.

Concept / Approach:
The modern view describes the strong nuclear force (residual strong interaction) between nucleons, often modelled historically as an “exchange force” (Yukawa meson exchange). In introductory treatments, “exchange forces” captures this short-range, saturating attraction. Gravitational and magnetic forces are far too weak at nuclear scales, and Coulomb forces are repulsive among protons, not binding.

Step-by-Step Solution:

Verification / Alternative check:
Potential form is short-ranged (falls rapidly beyond ~1–2 fm). This explains why distant nucleons do not bind strongly and why nuclear forces saturate, consistent with measured binding energies per nucleon.

Why Other Options Are Wrong:

• gravitational forces: Incredibly weak at subatomic masses.
• coulombic forces: Repel protons; cannot be the net binder.
• magnetic forces: Too weak and not the primary binding mechanism.

Common Pitfalls:
Answering “Coulombic” because it is a familiar term. Remember: Coulomb explains repulsion, not nuclear cohesion; the strong (exchange) interaction does the binding.

Final Answer:
exchange forces