GCSE PHYSICS - What is Background Radiation? - Radioactivity is a Random Process

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Background Radiation.

What is Background Radiation?

Radioactive nuclei (the source of radioactivity) are all around us.
Radioactive nuclei come from both natural and man made sources.

Natural radioactivity is found in the air, the ground and the sea.
Everything living is radioactive and food is also radioactive.
Radioactivity comes from rocks, particularly granite (see below).
Radiation also comes from space. Some comes from the Sun.
Some comes from other galaxies in space as gamma ray bursts.
These bursts may come from a distant star during a supernova.

Some man made radioactivity in the environment comes from
nuclear weapons testing and accidents at nuclear power stations.

All of this radioactivity is called the background radiation.
The level of this radiation (called the background count) is low.
If you switch on a Geiger counter it will detect this background
radiation and give a reading in Becquerels (Bq) for the level.

Radioactive Decay is a Random Process.

The background count is not constant but keeps going up and
down. This is because radioactive decay is a random process.
Remember the phrase, radioactive decay is a random process.
It will be useful in the exams. A random process
means that you don't know when the decay will happen.

On average, the background count might be 0·4 Bq.
At any one time, the background count might be 0, 1, 2 or 3 Bq.
To get an accurate reading for the background count
(or other radioactive source) you need to calculate the
average value of a large number of readings
which have been taken over a long period of time.

The background count is different in different parts of the country.
It is affected by the release of radioactive radon from rocks (granite).

When a Bq value for a radioactive material is given,
the background count is subtracted first.
The background count is subtracted because otherwise
the value would represent the radioactive source
plus the background count. This is particularly important if
the source is a weak emitter of radioactivity, where the
background count is a significant amount of the total reading.

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