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Topic 7: Atomic, nuclear and particle physics

See the guide for this topic.

7.1 – Discrete energy and radioactivity

When the electrons within an atom jump from one atomic energy level to a lower energy level, energy is released in the form of light. Likewise, light is absorbed when the electrons within an atom jump from one atomic energy level to a higher energy level.

The amount of energy absorbed or released can be calculated by the difference in energy (eV) between the two energy levels.

Alpha particles

 An alpha particle is a helium nucleus.

Beta particles

 A beta particle is an electron or a positron.

Gamma rays

See previous section (Radioactive decay).

Short-term effects Long-term effects
Ÿ   Radiation burn

Ÿ   Nausea and vomiting

Ÿ   Diarrhea

Ÿ   Headache

Ÿ   Cancer

Ÿ   Genetic mutations

Different isotopes of a given element have the same atomic number (atomic number defines the type of element) but different mass numbers because they have different numbers of neutrons.

Background radiation comes from natural sources and artificial sources.

Average composition and exposure of background radiation

7.2 – Nuclear reactions

The unified atomic mass unit (μ) is commonly used in nuclear physics. It is defined as one twelfth of the mass of a carbon-12 atom.

Mass defect

Nuclear binding energy

where E is energy in J, m is mass in kg, and c is the speed of light in m/s


The nuclear binding energy curve

Nuclear fission

Nuclear fusion

7.3 – The structure of matter

where u represents up quarks, d represents down quarks, c represents charm quarks, s represents strange quarks, (t represents top quarks), b represents bottom quarks, and the line above the representative letter of the quarks indicate its corresponding antiquarks.

See previous section in 7.2 (Fundamental forces and their properties).

Exchange particles of the four fundamental forces are gluons, photons, W+ bosons, W- bosons, Z0 bosons, and gravitons.

See previous section in 7.2 (Fundamental forces and their properties).

Some examples of Feynman diagrams

For a comprehensive guide on how to draw Feynman diagrams, visit

Quarks and gluons (massless subatomic particles that transmit the force binding quarks together in a hadron) are color-charged particles. Similar to electrically-charged particles which interact by exchanging photons in electromagnetic interactions, color-charged particles exchange gluons in strong force interactions. Note that color charge has nothing to do with visible colors. It is just an expression.

When two quarks are close to each other, they exchange gluons and create a strong color force field that binds quarks together. The force field gets stronger as the quarks get further apart. Quarks constantly change their color charges as they exchange gluons with other quarks. There are 3 color charges and 3 corresponding anti-color charges.

Just as mixing red, blue, and green visible colors yield white, mixing red, blue, and green color charges yield color neutral.

Color confinement is a phenomenon that color-charged particles cannot be isolated singularly and therefore cannot be directly observed. The color-charged quarks are said to be confined in groups (hadrons) with other quarks which composite to color neutral and cannot be distinguished separately. This is because the color force increases as the color-charged quarks are pulled apart.

TL;DR: Color confinement or quark confinement is the phenomenon when isolated quarks and gluons cannot be observed.

In addition to the three generations of leptons and quarks (see previous section (Quarks, leptons and their antiparticles)), there are four classes of bosons and an additional highly massive boson called the Higgs boson. This particle was proposed in 1964 to explain the process which particles can acquire mass and was identified with the Large Hadron Collider (LHC).


The Large Hadron Collider (LHC) is the world’s largest and most powerful particle collider, the largest and most complex experimental facility ever built, and the largest single machine in the world. It was built by CERN in collaboration with over 10000 scientists and engineers from over 100 countries along with hundreds of universities and laboratories.

Our changing views of the atom model

Summary of fundamental particles and interactions

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