Additional Physics Topic 6

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  • Created by: Hannah
  • Created on: 20-11-12 18:17

A GM tube is a tube which detects ionising radiation. An ionising radiation such as alpha, beta and gamma are placed inside of the tube. The particles in the air become charge due to the ionising radiation and begin to move. This creates a flow of charge which is current. Current is electrical energy which is converted into sound energy. This is how you get the clinking sound so this means that we can count the number of ionised particles.

Background radiation is the ionisng radiation constantly present in the natural enviroment of the Earth which is emitted by natural and artifical sources.


  • Radon gas from the ground. Certain underground rocks, such as granite can caus higher levels of background radiation at the surface. These typically contain radioactive radon gas which gets trapped inside peoples home. The radon concentration varies across the UK as it depends on the type of rock that your house is built on. Therefore, the amount of radon gas that people is exposed to differs from region to region.  
  • Cosmic rays- these come mostly from the sun, but the Earth's atmosphere protects us from the large amount of this energy and the magnetic field deflects the cosmic rays away from us
  • Gamma rays from rocks


  • Nuclear Power and testing
  • Food and Drink
  • Medical sources.

Radon gas accounts for 50.1% of the background radition. Grounds and buildings are 13.5%, Medical use is 14.3%, Food and drink is 11.6%, Cosmic rays are 10% and other sources are 0.5%.

Radon gas occurs when the atoms of uranium 238 decay. You cannot see, hear, taste or feel radon gas so when it is inhaled, it will emith alpha particles which damage the internal lung surface and it also dislodges the electrons that hold the DNA together which can cause a number of chemical changes in the body. This can lead to cancer. The most effective way of protecting yourself against radon gas it to fit air pumps into the person's property which vents the gas into the atmosphere.

The activity (symbol A) of a source is the rate of decay of a nuclei. It is measured in the unti Becquerel (Bq).

For example, if a sample has an activity of 1000Bq, it means that their is 1000 nuclei decaying every second.

The activity depends on:

  •  the mass of the sample: if we double the the mass , we double the activity. It means that the mass and the activity are directly proportional.
  • how long the sample lasts: if we double the time a sample lasts, we halve the activity. This is indirectly proportional.

As the unstable nuclei disspears, the activity will decrease as a whole, so the longer the source lives, then the less reactive it will become. Some isotopes, only takes a few hours before it has nearly all decayed away as for others, some will last for a millon years.

Each radioactive element has it own particular decay rate, which is called half life. Half-life is used…


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