Radioactive Decay (Oxford AQA IGCSE Physics)

Revision Note

Radioactive Decay

Unstable nuclei

  • Some atomic nuclei are unstable

  • Carbon-14 is an isotope of carbon which is unstable

    • It has two extra neutrons compared to stable carbon-12

Carbon-12 and Carbon-14

The nucleus of carbon-14 contains an imbalance of protons and neutrons and is unstable, IGCSE & GCSE Physics revision notes
Carbon-12 is stable, whereas carbon-14 is unstable. This is because carbon-14 has two extra neutrons
  • Some isotopes are unstable because of their large size or because they have too many or too few neutrons

Radiation

  • Unstable nuclei can emit radiation to become more stable

    • Radiation can be in the form of a high-energy particle or wave

Radiation emitted from a nucleus

Radioactive decay of a nucleus by the emission of radiation, IGCSE & GCSE Physics revision notes
Unstable nuclei decay by emitting high-energy particles or radiation
  • As the radiation moves away from the nucleus, it takes some energy with it

    • This reduces the overall energy of the nucleus

    • This makes the nucleus more stable

  • The process of emitting radiation is called radioactive decay

  • Radioactive decay is a random process

    • This means it is not possible to know exactly when a particular nucleus will decay

Worked Example

Which of the following statements is not true?

A

Isotopes can be unstable because they have too many or too few neutrons

B

The process of emitting particles or waves of energy from an unstable nucleus is called radioactive decay

C

Scientists can predict when a nucleus will decay

D

Radiation refers to the particles or waves emitted from a decaying nucleus

Answer:  C

  • Answer A is true. The number of neutrons in a nucleus determines the stability

  • Answer B is true. This is a suitable description of radioactive decay

  • Answer D is true. Radiation is about emissions. It is different to radioactive particles

  • Answer C is not true

    • Radioactive decay is a random process

    • It is not possible to predict precisely when a particular nucleus will decay

Examiner Tip

The terms unstable, random and decay have very particular meanings in this topic. Remember to use them correctly when answering questions!

Detecting radiation

  • Radiation that is emitted from an unstable nucleus can be detected in different ways

    • For example, photographic film changes colour when exposed to radiation

  • A Geiger-Muller tube is a device used to detect radiation

A Geiger-Muller tube

Geiger-Muller tube, also called a Geiger counter, for IGCSE & GCSE Physics revision notes
This Geiger-Muller Tube is connected to a Geiger Counter. This a common way of detecting radiation and measuring a count-rate
  • Within the Geiger-Muller tube, ions are created by radiation passing through it

  • The Geiger-Muller tube can be connected to a Geiger counter

  • This counts the ions created in the Geiger-Muller tube

  • The count rate is the number of decays recorded each second by a detector

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