[2]These devices, which will be frequently mentioned later in these pages, are described in detail in a companion booklet _Power from Radioisotopes_. [3]See _Nuclear Reactors_, another booklet in this series, for a description of the fission process and how reactors operate. [4]For a full discussion of other aspects of this topic, see _Fallout from Nuclear Tests_, another booklet in this series. [5]For a full discussion of this topic, and the safety measures taken by the AEC in connection with it, see _Radioactive Wastes_, another booklet in this series. [6]Radioisotopes, unstable forms of ordinary atoms, are distinguishable by reason of their radioactivity, not by their biological or chemical activity. [7]The time in which half of the atoms in a quantity of radioactive material lose their radioactivity. [8]For more details of these studies, see _Atoms, Nature, and Man_, a companion booklet in this series. [9]Gamma rays are high-energy electromagnetic radiation, similar to X rays, originating in the nuclei of radioactive atoms. [10]Instruments that detect and measure radiation by recording the number of light flashes or scintillations produced by the radiation in plastic or other sensitive materials. [11]A method involving use of nuclear reactors or accelerators for identifying extremely small amounts of material. See _Neutron Activation Analysis_, a companion booklet in this series. [12]A picogram is one trillionth (10⁻¹²) of a gram. [13]For an explanation of how similar instruments work, see _Radioisotopes in Industry_, a companion booklet in this series. [14]For a discussion of proposed nuclear merchant submarines, see _Nuclear Power and Merchant Shipping_, another booklet in this series. [15]These are described in _Power Reactors in Small Packages_, another booklet in this series. [16]See _Power from Radioisotopes_, a companion booklet in this series, for a more complete discussion of radioisotopes in use. [17]For an explanation of how these will function, see _Nuclear Energy for Desalting_, another booklet in this series. [18]See _Food Preservation by Irradiation_, another booklet in this series, for a full account of this installation. [19]Details are described in _Plowshare_, another booklet in this series. This booklet is one of the “Understanding the Atom” Series. Comments are invited on this booklet and others in the series; please send them to the Division of Technical Information, U. S. Atomic Energy Commission, Washington, D. C. 20545. Published as part of the AEC’s educational assistance program, the series includes these titles: