Go back to Nuclear Radiation & Radioactivity
The words "radioactivity" and "radiation" come from "radius".
RADIATION means any sort of an energy form spreading out from a centre. Radio waves, light, infrared light and microwaves are all examples of radiation. These types of radiation are all related, they are members of the ELECTROMAGNETIC SPECTRUM and all travel at the speed of light, 3 x 108ms-1.
The radiation associated with radioactivity, however, is far more violent, that is, energetic. This radiation is classed as IONISING RADIATION as the radiation from the nuclei can easily destroy molecules by stripping away electrons from their atoms - ionising them. (Other Ionising Radiation includes UV light and X-rays. Both of these are members of the Electromagnetic Spectrum.)
The radiation from nuclear processes are not
necessarily members of the Electromagnetic Spectrum. Two forms are actually
"particles"- but come from the nucleus itself as the change occurs.
The three common natural types of radiation from nuclear decay are;
α radiation (alpha) 
- a helium atom nucleus. This is a "slow" moving particle, with a
short range in air. Alpha particles are extremely dangerous inside
the body but not very dangerous outside as they cannot penetrate the skin.
The speed of αradiation
is about 0.1 of the speed of light.
The radiation has two elementary positive charges
and the particle has considerable mass.
β radiation (beta) -
an electron 
or β- ejected
from the nucleus when a neutron changes spontaneously to a proton. These
are moving fast, about 0.9 of the speed of light, they can get through
skin and have a reasonably long range in air (about one metre ).
These have only a little mass, and are negatively charged.
βradiation is dangerous
if ingested.
γ radiation (gamma) 
; this is a very energetic form of electromagnetic radiation. Compared to
light , each bit (photon) has 1 million times as much energy ( or 1 thousand
times more energy than an X-ray photon).
They travel at the speed of light. They happily travel through centimetres of lead and travel easily through air. They are a danger to the human body even when not ingested due to this penetrative ability.
Gamma radiation
has no charge associated with it.
Nuclear decays and reactions produce other forms of radiation as well. Some are from artificial elements, some are products of splitting atoms.
Neutrinos, antineutrinos, 
,
; weird neutral particles
which are emitted with electrons in beta decay. They can be ignored for
the purpose of this course.
β+ ; an antielectron
or positron 
. It
has all the same characteristics of a normal electron except for having
the same charge as the proton and the disconcerting habit, if it meets
an ordinary electron, of turning itself and the electron into gamma rays!
(All "antimatter" will do this on meeting the matter counterpart!)
n;
a neutron,- emitted as a side product of nuclear fission. Solo neutrons
have a half life of about 10 minutes. They easily pass through steel plating
and large doses finally have deadly consequences. Neutron bombs are fission
bombs with less blast but more leaky neutrons. They therefore do less damage
to factories but kill very satisfactorily.
All radiation can be absorbed to "negligible" levels by sufficient material and, of course, the further one is from the source, the smaller the received dosage. (Recall that radiation means spreading out from a centre. The further from that centre you are the more the radiation energy has spread out.)
Because of the energy of the radiation, radioactive sources can fog photographic film. This technique is used to crudely monitor dosage for people who work with the materials.