SCIENCE PHOTO LIBRARY SCIENCE PHOTO LIBRARY
In a series of classic cloud chamber experiments in the late 1920s, English physicist Patrick Blackett obtained clear evidence of how alpha particles scatter from atomic nuclei of different masses. In this false-colour version of one of his pictures, alpha particles stream upwards through the chamber. One of them (yellow) scatters a nucleus (also yellow) in the helium gas filling the chamber. The two particles move off at a 90- degree angle, revealing that they have the same mass - alpha particles are helium nuclei. Compare with photos A132/004 & A132/005.
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