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Subatomic particle tracks: coloured bubble chamber photograph from CERN, the particle physics lab at Geneva. A positive kaon, coming from the top, decays near the centre into three pions. Two are positive pions which curve clockwise in the bubble chamber's magnetic field, towards bottom right & top left. Each decays into a positive muon (short kink at the end of each pion track) which decays in turn into a positron that forms a spiral track. The third, negative pion describes a shallow anticlockwise curve downwards before decaying to a negative muon (short kink). The other tracks and spirals are not part of this event. (KEYSTONE/SCIENCE PHOTO LIBRARY/GORONWY TUDOR JONES, UNIVERSITY OF BIRMINGHAM)