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====Sources of Background Radiation====
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|[[File:BackgroundRadiation.png|center|300px]]
| style="height:20px; width:300px; text-align:left;" |'''Food''':
Many of our foods contain small quantities of radioactive isotopes. Figure A shows a Banana containing Potassium-40, a gamma emitter. The Potassium-40 in your body means the average person emits around 108 gamma rays every second.
'''The Ground''': Rocks under the ground have small quantities of radioactive isotopes and so gamma rays are being emitted from beneath our feet all the time.
'''Radon Gas''': Rocks containing Uranium decay by alpha emission to Radium and then Radium decays into Radon. This gas escapes through cracks in the ground and we breath in the radioactive radon.
'''[[Cosmic Ray]]s''': The explosions of stars throughout space sends out extremely fast moving particles. Many of these arrive at earth. When they do they are usually stopped by atoms in the atmosphere. However some few will make it to the ground, so we are constantly bombarded by tiny pieces of debris from exploding stars.
'''Medical Uses''': Modern medicine uses a number of techniques which rely on radioactive isotopes or other sources of ionising radiation. There is a limited number of X-rays, CAT scans and PET scans you are allowed to have in a year in order to stop you receiving a dangerous dose.
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