Ernest Rutherford's discovery of the atomic nucleus in 1911 neatly solved one problem in atomic theory--the relative distribution of positive and negative charges in the atom. Consequently, new questions regarding the structure and composition of the nucleus itself were raised.

One method for answering that question was pursued by Rutherford himself. He directed alpha particle s from naturally radioactive materials at the nuclei of atoms, attempting to "blow apart" those nuclei. The products obtained from such an experiment, Rutherford felt, would reveal the body's composition.

Although Rutherford achieved some success with this research, he also recognized certain limitations. The number and energies of the particles available from natural sources limited his control over the experiment. He had to use whatever particles his source provided him. At the time, no technique was available for accelerating alpha particles, protons, or other particles by artificial means that would give an investigator precise...