Radioactive Decay (HT only)
Unstable Nuclei
- Some atomic nuclei are unstable
- This is because of an imbalance in the forces within the nucleus
- Forces exist between the particles in the nucleus
- Carbon-14 is an isotope of carbon which is unstable
- It has two extra neutrons compared to stable carbon-12
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
Unstable nuclei decay by emitting high energy particles or waves
- 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
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- 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!