National Geographic : 1954 Jan
72 National Geographic Photographer Robert F. Sisson Uranium Atom's Tightly Clustered Core Is the Main Source of Atomic Energy Shown in Boston's Museum of Science, this model depicts radioactive uranium 235, whose nucleus consists of 92 protons and 143 neutrons. Nonfissionable uranium 238 carries three additional neutrons. Both are isotopes, or variants, of Nature's heaviest element. Balls bunched in the center represent the protons and neutrons, which are mysteriously bound together by atomic energy's terrific force. Splitting of the nucleus releases energy far greater than that of any chemical reaction. Wire-strung balls swinging like planets around a sun represent uranium's 92 electrons. Hydrogen, in contrast, has one. True scale would place the outermost electrons 3,000 feet from center.