Radioactive Decay (Oxford AQA IGCSE Combined Science Double Award)
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
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
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
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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