C.T.R. WILSON / SCIENCE PHOTO LIBRARY C.T.R. WILSON / SCIENCE PHOTO LIBRARY
Cloud chamber photograph of the track of a fast beta ray. Beta rays are electrons moving at high speed; they are emitted during radioactive decay - beta decay - of certain radioactive materials, & they can also be knocked out of atoms by X-rays or gamma rays. The beta ray travels up the picture; it leaves a faint, intermittent track because it is fast-moving. The denser, squiggly tracks in the picture are produced by less energetic electrons which have been knocked from atoms in the cloud chamber's gas by invisible X-rays. The photo was taken by English physicist C.T.R. Wilson, the inventor of the cloud chamber, & was published in 1923.
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