Headings Radioactivity Search
Questions 
gcsescience.com 15 gcsescience.com
Background Radiation.
Radioactive nuclei (the source of radioactivity) are all
around us.
They are found naturally in the
air, the ground and the sea.
Everything living (and food) is
also radioactive.
Radiation also comes from space.
Some comes from the Sun,
some comes from all directions as gamma ray bursts.
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 for the
level.
The reading is not
constant but keeps going up and down.
This is because radioactive decay is a
random process
(remember this phrase, 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.
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 might be a
significant amount of the total reading.
Headings Radioactivity Search
Questions
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