3: Tandem van de Graff accelerators are used to accelerate nuclear particles to high energies. Beams of these particles can be used to study nuclear reactions and nuclear structure. Another use for such beams is the treatment of cancerous tumors. It turns out charged particles lose energy as they interact with matter by ionizing the medium they pass through. One of the more fortunate aspects of this energy loss is that most of the energy is dumped right at the end of the particle's path. If one tunes the energy of a particle beam so that the average range of the particle through the body is just sufficient to reach the tumor, most of the energy is released in the tumor, destroying only the tissue you would like to destroy. Cool, huh?!