Gamma Rays!!! Below we find an electron (top) smashing into an anti-electron, called a positron(bottom), and releasing a high energy gamma ray! This ray might go on to form twin mesons, but not in this picture. Gamma radiation occurs when a particle changes to a lower energy state and is forced to give up some of it's surplus energy to do so. When this energy is released, it may be in the form of a photon. Very high energy photons are called Gamma Rays. Gamma rays have frequencies of greater than 10 exahertz and energies greater than 100 keV!!! These incredibly powerful photons tear through normal matter, such as pine cones, a platypus, or your DNA, changing the configuration of anything they touch. Student - "So... light is made of photons and so are Gamma rays... so Gamma rays are light?" Teacher - "No. Soda cans are aluminum and so is foil, but are they the same?" Student - "No..." Teacher - "A photon with lots of energy may be a gamma ray, but at a lower energy it may be light." Student - "Oh, I see! I can stop light with my hand. Can my hand stop gamma rays?" Teacher - "No... It may take many feet of lead to stop gamma rays!!!" Student - "Will gamma radiation give me super powers?" Teacher - "It will give you cancer... not quite a super power..." Teacher Monologue: "The ability of a material to stop a ray or particle of radiation is based upon the average probability of deflection and incidence. As a particle moves past atoms, it looses energy as it is deflected and refracted about. As rays of energy pass atoms they collide and come to a crashing end. It is much like flying a hang glider through a forest. If you do it many times, you are stupid... but you might have a change of hitting the first tree or perhaps making it a good distance. Likewise, a gamma ray might be stopped by the very first atom of lead in a wall or make it ten miles! What we are looking for is how much lead is needed to stop, on average, a give percent of the radiation. We choose lead because it is very dense and bonds relatively close to other lead atoms. Uranium, ironically, makes a good shield. Air actually stops things too! Remember, all rays and particles in out atmosphere can bump into an atom of oxygen, nitrogen, carbon, or other things." Student - "Duh... ok!"