Gamma rays are like X rays, only much more energetic and harmful to humans. Fortunately for us, the gamma radiation produced in outer space and by our sun is absorbed by our atmosphere and we are shielded from its effects.

It is not possible to create images of gamma-emitting objects in space. When incoming gamma photons strike a large crystal of sodium iodide, they are converted into visible photons that can be counted. Thus gamma sources can be located in space, but not imaged.

1. Gamma rays are produced on earth by the decay of radioactive elements and in nuclear reactors. If your school has a Geiger or scintillation counter, you may observe the presence of gamma rays from an appropriate radioactive element. Be sure your instructor helps you with this activity!

2. If you have a gamma source available, place sheets of lead foil between the source and the counter. Observe the count rate as you place more and more sheets of foil over the source. How many sheets are required to reduce the count rate by one half? How thick is the stack of lead sheets needed to reduce the count rate by one half?

3. If you were an astronaut living on the proposed Space Station, how would you protect yourself from gamma radiation from space? How long do you think you could stay on the station without risking your health?

©1997 Exploratorium