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
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 scintilation
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
Created 1997 The Exploratorium
Regents of the University of California