Hans Geiger (1882-1945) worked closely with Ernest Rutherford (1871-1935) to develop radiation measuring devices. In this early example a low presure gas is held in a copper cylinder fitted with a handle. An electrical current is then applied between the copper casing and a thin wire running along its centre. The particle entering the cylinder causes a burst of electric current which is registered on a counter. This particular Geiger counter was used by James Chadwick, the discoverer of the neutron.
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