Dr Lothar Koch, German nuclear chemist. Koch is head of the nuclear chemistry department of the European Trans-Uranium Institute (ETUI) at Karlsruhe, Germany. This is the laboratory where samples of contraband nuclear materials (such as plutonium) picked up by Customs or Police officers are tested in order to determine their place of origin. This may be achieved by using a glow discharge mass spectrometer to detect and quantify any impurities such as americium or gallium in the sample. The presence and quantity of impurities acts as a 'signature', allowing the country of origin or even the source production facility to be identified. Photographed in 1994.