There are Z protons in the nucleus of an atom, where Z is the atomic number of the element. An α particle carries a charge of +2e. In a scattering experiment, an α particle, heading directly toward a nucleus, will come to a halt when all the particle's kinetic energy is converted to electric potential energy. In such a situation, how close will an α particle with a kinetic energy of 6.40×10−13 J come to a nucleus with atomic number Z = 68? Number Units
