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Radioactivity analysis. Researcher checking river water for ionising radiation levels. He is using a conductivity meter which works by passing an electric current between two electrodes (lower left) in the water. The presence of ionising radiation, comprising charged particles and gamma rays, causes the water's conductivity to increase. This work is being carried out by the French government agency, l'Institut de Protection et de Secrete Nucleaire (IPSN). Photographed near the Tinee River, France. (KEYSTONE/SCIENCE PHOTO LIBRARY/PASCAL GOETGHELUCK)