C.T.R. WILSON / SCIENCE PHOTO LIBRARY C.T.R. WILSON / SCIENCE PHOTO LIBRARY
Cloud chamber photograph of the final portion of the track of an alpha particle. The photo was taken in 1912 by English physicist C.T.R. Wilson, the inventor of the cloud chamber, & was one of the earliest pictures made with the instrument. The picture shows that the track changes direction where the alpha particle collides with atoms in the air inside the cloud chamber. Finally, close to its end, the track becomes fainter as the positively charged alpha particle captures electrons & loses its charge. Alpha particles are now known to be nuclei of helium atoms. They form one of the three types of radiation - with beta & gamma rays - emitted by radioactive materials.
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