Strong Nuclear Force Notes

Discovery of Fundamental Forces

• Built on work of Dalton, Thompson, Rutherford, and Bohr

• 20th-century scientists discovered that protons & neutrons (nucleons) are held together in the nucleus by the Strong Nuclear Force

Strong Nuclear Force

• One of the Four Fundamental Forces

  • Others: Gravity, Electromagnetic Force, Weak Nuclear Force

• Strongest of the four forces

• Shortest range – only acts when particles are extremely close

How Does the Strong Nuclear Force Work?

• Like charges repel (+ vs. + or - vs. -)

• Unlike charges attract (+ vs. -)

• Protons in the nucleus are all positively charged, so they should repel each other (repulsive force)

How Do Protons in an atomic nucleus Stay Together?

• strong nuclear force is created by nucleons exchanging particles called mesons.

Conditions for strong nuclear force to work

• As long as mesons are exchanged, the Strong Nuclear Force holds nucleons together

• nucleons must be extremely close together, in order for exchange to happen.

• If a proton or neutron gets close enough to another nucleon → Meson exchange happens → Particles stick together

• 
  If Nucleons Are Too Far Apart

  • Strong Nuclear Force weakens

  • Electromagnetic force (repulsion between protons) takes over → Particles move apart

Electrostatic Repulsion (Barrier to Strong Force)

• Dotted line around a nucleon (proton or neutron) represents the electrostatic repulsion (proton repelling proton)

• To activate the Strong Nuclear Force, a nucleon must cross this barrier

Proton-Proton Repulsion

• As a proton approaches another proton, it feels increasing repulsion due to the electromagnetic force

• To overcome this repulsion and allow meson exchange, nucleons must get extremely close

Overcoming barriers to create strong nuclear force and to get Nucleons to get 2 nucleons close together to begin exchange mesons.

✔ Extremely high speed (high temperature) 🔥
✔ Immense pressure (forced closer together) 💥

Role of Neutrons in strong nuclear force

• Neutrons have no charge → They do not contribute to electrostatic repulsion

• Neutrons separate protons → This weakens the repulsive force between protons forcing nucleons to stay bound together

• neutrons can participate in meson exchange

Role of neutrons in experiment

Better than protons for this task because:
✔ No charge → Not repelled by the positively charged nucleus
✔ Can easily pass through the electrostatic repulsion barrier

Changing the Number of Neutrons Affects the Nucleus

• Mass changes → Creates radioactive isotopes

• Energy changes → Can trigger chain reactions (used in nuclear reactors & atomic bombs 💥)