I.

Introduction

Uranium, symbol U, chemically reactive radioactive metallic element that is the main fuel used in nuclear reactors. Uranium is a member of the actinide series in the periodic table (see Periodic Law). The atomic number of uranium is 92.

Uranium was discovered in 1789 in the mineral pitchblende by the German chemist Martin Heinrich Klaproth, who named it after the planet Uranus. It was first isolated in the metallic state in 1841. The radioactive properties of uranium were first demonstrated in 1896 when the French physicist Antoine Henri Becquerel produced, by the action of the fluorescent salt potassium uranyl sulfate, an image on a photographic plate covered with a light-absorbing substance. The investigations of radioactivity that followed Becquerel's experiment led to the discovery of radium and to new concepts of atomic organization. See Atom; Nuclear Energy.