Atoms and ionising radiation

Isotopes are different forms of the same element. 

Isotopes are atoms with the same number of protons but a different number of neutrons.

They have the same atomic number but have a different mass number.

The atomic number is the number of protons in an atom.

Mass number is the number of protons + the number of neutrons in an atom.

Carbon-12 and carbon-14 are good examples of isotopes.

Radioactive substances give out radiation from the nuclei of their atoms.

This process is random and this means if you have 1000 unstable nuclei, you can't say when any of them is going to decay and nothing can be done to make the decaying process happen.

It's unnafected by physical conditionslike temperature or by chemical bonding.

Radioactive substances spit out one or more of the three types of radiation - alpha, beta or gamma. 

Background radiation comes from many sources.

Background radiation is present all the time and is everywhere we go.

Background radiation comes from:

Radioactivity of naturally occuring unstable isotopes which are all around us - in the air, in food, in building materials and in the rocks under our feet.

Radiation from space, which is known as cosmic rays. These come from the sun.

Radiation due to man-made sources like nuclear weapons tests, nuclear accidents (like what happend at Chernobyl) or dumped nuclear waste.