One of the most important tools of nuclear science is the particle accelerator. Prior to its invention in 1932, the only known sources of particles that could induce nuclear reactions were the natural alpha particle emitters, for example radium. In fact, the only type of nuclear reaction known during that period was that of an alpha particle interacting with a nucleus and producing a proton. Today the use of natural alpha emitters to induce nuclear reactions is largely of historical interest because accelerators produce higher intensities and higher energies of not only alpha particles, but of most elements between hydrogen and uranium.