By the late 1890s, it had become obvious to scientists that John Dalton's (1766-1844) concept of a solid, indivisible atom was incorrect. In 1897 Joseph J. Thomson (1856-1940) showed that even smaller particles--electrons--could be removed from an atom. A decade later, Ernest Rutherford (1871-1937) identified another structure within the atom, a central body that he called the nucleus. The next stage in learning about the composition of matter seemed to be to explore this new structure, the atomic nucleus.

During the late 1910s, Rutherford himself carried out some of the earliest experiments in this area. He directed alpha particles from naturally radioactive materials at gases confined within a glass tube. He found that the alpha particles collided with and broke apart the nuclei of the gaseous atoms. These experiments constituted the first example of atom smashing, the process by which an atomic nucleus is broken apart in...