Background Radiation

Some substances give out radiation all the time, whatever is done to them. These substances are said to be __________. Radioactivity occurs as a result of changes in the __________ of atoms (nuclear changes). When an unstable nucleus __________ (disintegrates):

• it emits __________;
• a __________ atom, with a different number of protons, is formed.

There are radioactive substances all around us, including in the ground, in the air, in building materials and in food. Radiation also reaches us from __________. The radiation from all these sources is called __________ radiation.

Source		Percentage
__________	Radon gas	50.0%
	Ground and buildings	14.0%
	Food and drink	11.5%
	Cosmic rays	10.0%
__________	Medical	14.0%
	Nuclear power & weapons	0.3%
	Other	0.2%

There are regional __________ in background radiation, as the map indicates. This is manily due to the release of __________ from some igneous rocks as urainium decays.

When conducting experiments we must measure the __________ background radiation and take it away from our results. In order for this to give results with an acceptable degree of accuracy, the background radiation should be no more than 10% of the activity.

The Earth's atmosphere and magnetic field protects us from the cosmic rays produced by the Sun.