Physics (5054)
Topic 10 of 10Cambridge O Levels

Nuclear Physics & Radioactivity

Atomic structure, alpha/beta/gamma radiation, half-life, fission and fusion

An atom has a nucleus (protons + neutrons) surrounded by electrons in shells. Isotopes are atoms with the same number of protons but different neutrons.


Radioactive decay is when unstable nuclei emit radiation:

  • Alpha (α): 2 protons + 2 neutrons (helium nucleus). Stopped by paper. Most ionising. Least penetrating.
  • Beta (β): High-speed electron from the nucleus. Stopped by aluminium. Medium ionising.
  • Gamma (γ): Electromagnetic wave. Stopped by thick lead. Least ionising. Most penetrating.

    • Half-life = time for half the radioactive atoms to decay (or activity to halve). After 3 half-lives: 1/8 remains.


    Nuclear Fission: Heavy nucleus (e.g. uranium-235) splits into two smaller nuclei + neutrons + energy. Used in nuclear power stations. Chain reaction when neutrons hit more nuclei.


    Nuclear Fusion: Light nuclei (e.g. hydrogen) join to form heavier nucleus + energy. Powers the Sun. Requires extreme temperature and pressure.

    Key Points to Remember

    • 1Alpha stopped by paper, beta by aluminium, gamma by thick lead
    • 2Half-life: time for activity to halve
    • 3Fission: heavy nucleus splits, releases energy
    • 4Fusion: light nuclei join, powers the Sun

    Pakistan Example

    Radiation in Pakistan — From PINSTECH to Cancer Treatment

    Pakistan's PINSTECH nuclear research centre in Islamabad studies radioactive isotopes. Hospitals like Shaukat Khanum use gamma radiation in radiotherapy to kill cancer cells. Pakistan's nuclear power plants (KANUPP in Karachi, Chashma in Punjab) use uranium fission to generate electricity.

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