Radioactive Emissions
- Some atomic nuclei are unstable and radioactive
- This is because of an imbalance of protons or neutrons in the nucleus
- Carbon-14 is an example of an isotope of carbon which is unstable
- This is because it has two extra neutrons compared to a stable nucleus of carbon-12
Stable and Unstable Isotopes of Carbon
Carbon-12 is stable, whereas carbon-14 is unstable because it has two extra neutrons
- Unstable nuclei can emit radiation to become more stable
- Radiation can be in the form of a high-energy particle or wave
- This process is known as radioactive decay
- As the radiation moves away from the nucleus, it takes some energy with it
- This makes the nucleus more stable
Radioactive Decay of a Nucleus
Unstable nuclei decay by emitting high energy particles or waves
Detecting Radiation
- Radioactive decay is a random and spontaneous process
- This means it is not possible to know exactly when a particular nucleus will decay
- This is important to understand when undertaking experimental work involving radioactive decay
- A common device used to measure and detect radiation is called a Geiger-Müller tube
- Each time it absorbs radiation, it transmits an electrical pulse to a counting machine
- This makes a clicking sound or displays the count rate
- The greater the frequency of clicks, or the higher the count rate, the more radiation the Geiger-Müller tube is absorbing
- Therefore, it matters how close the tube is to the radiation source
- The further away from the source, the lower the count rate detected
A Geiger-Müller Tube
A Geiger-Müller tube (or Geiger counter) is a common type of radiation detector
- To reduce the effect of random fluctuations in the measurements:
- Readings should be repeated and averages taken
- Background radiation must be subtracted from the readings
- The readings should be taken over a long period of time
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
Exam Tip
The terms unstable, random and decay have very particular meanings in this topic. Remember to use them correctly when answering questions!
