There are four types of radiation commonly arising from the use of radioactive agents. They vary in lethality and effects and the type and amount of shielding required to protect against them.

Alpha radiation

Alpha radiation is the result of radioactive decay of certain specific radionuclides. Alpha radiation is basically particulate in nature. Alpha particles are composed of two protons and two neutrons, making them physically equivalent to the nucleus of a helium atom. Because alpha particles are comparatively large and heavy, they are not able to travel far - no more than a few inches through air. However, also as a result of their size and weight they are very destructive if they do contact living tissue. This is most likely to occur if the affected person inhales dust which contains alpha emitting metal particles. A single grain of dust containing an alpha emitter will almost certainly cause cancer if inhaled.

Beta radiation

Beta radiation is the result of radioactive decay of certain nuclides, but by a different mechanism than alpha emission. Some materials may emit both during their decay. Beta radiation is basically particulate in nature. Beta particles are composed of single electrons. Because beta particles are comparatively small and light, they are slightly more penetrating than alpha particles. Beta radiation can be detected up to several feet from the source, but a single sheet of ordinary paper will block it completely. Beta radiation is not as damaging as alpha radiation, but is still likely to cause cancer if an emitter is inhaled.

Gamma radiation

Will not turn you into the Incredible Hulk. Gamma radiation is produced by many natural processes, and some radioactive decay events will emit gamma rays. Gamma radiation is basically electromagnetic radiation, just as is light, radio waves and X-rays. It has a very short wavelength and high energy. Because of this, it is very penetrating. Shielding against gamma radiation requires thick layers of lead or concrete. Most radiation sickness in the aftermath of a nuclear attack will be due to the immediate exposure to gamma radiation from the initial blast¹, from continued exposure to residual gamma emitters in fallout, and exposure to gamma emitters near the centre of the blast by people entering that area in the immediate aftermath of the blast.

Neutron radiation

Neutron radiation is a by-product of fission and fusion reactions and certain types of radioactive decay. Neutron radiation is simply a stream of high energy neutrons, uncharged heavy-ish subatomic particles. Because of its lack of charge, neutron radiation is quite penetrating (although not as much as gamma), but because it is also a basically quite massive particle it is also more immediately damaging. This led in the seventies to the development of the high-yield neutron bomb which was aimed to minimise blast damage but maximise the delivered neutron radiation dose - leaving buildings standing but killing the occupants.