Summary
Types of Radiation:
Alpha Particles
Alpha particles can be shielded by a sheet of paper or by human skin. However, if radionuclides that emit alpha particles are inhaled, ingested, or enter your body through a cut in your skin, they can be very harmful.
Beta Particles
Beta particles cannot be stopped by a sheet of paper. Some beta particles can be stopped by human skin, but some need a thicker shield (like wood) to stop them. Just like alpha particles, beta particles can also cause serious damage to your health if they enter your body. For example, if ingested, some radionuclides that emit beta particles might be absorbed into your bones and cause damage.
Gamma and X-Rays
Gamma rays are the most penetrating of the three types of radiation listed here. Gamma rays usually accompany beta, and some alpha rays. Gamma rays will penetrate paper, skin, wood, and other substances. To protect yourself from gamma rays, you need a shield at least as thick as a concrete wall. This type of radiation causes severe damage to your internal organs. (X-rays fall into this category, but they are less penetrating than gamma rays.)[1]
Copyright status
This image has been released into the public domain by its author, Tungsten. This applies worldwide.In some countries this may not be legally possible; if so:Tungsten grants anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law.
Source
http://commons.wikimedia.org/wiki/Image:Alfa_beta_gamma_radiation.png
