When a charged particle moves through matter it loses energy primarily to excitation and ionization of the atoms in the medium. It also loses some energy due to collisions with nuclei in the medium. As it loses energy, it moves more slowly and eventually stops. The distance it travels is called its range. The range depends on many parameters that include the charge, mass and initial energy of the particle, and the density, ionization potential and atomic number of the atoms in the medium. In this experiment, you will use cardboard, copper foil, aluminum plate and lead sheet to block beta particles. If you had equal thicknesses of each substance, which would be most effective blocker? Which would be the least effective blocker?