An alpha particle (two protons, two neutrons) moves into a stationary gold atom (79 protons, 118 neutrons), passing through the electron region that surrounds the gold nucleus like a shell and headed directly toward the nucleus (Fig. below). The alpha particle slows until it momentarily stops when its center is at radial distance r =9.23 fm from the nuclear center. Then it moves back along its incoming path. What was the kinetic energy Ki of the alpha particle when it was initially far away? Assume that the only force acting between the alpha particle and the gold nucleus is the (electrostatic) Coulomb force and treat each as a single charged particle. Alpha particle Gold nucleus Lightshot

An alpha particle (two protons, two neutrons) moves into a stationary gold atom (79 protons, 118 neutrons), passing through the electron region that surrounds the gold nucleus like a shell and headed directly toward the nucleus (Fig. below). The alpha particle slows until it momentarily stops when its center is at radial distance r =9.23 fm from the nuclear center. Then it moves back along its incoming path. What was the kinetic energy Ki of the alpha particle when it was initially far away? Assume that the only force acting between the alpha particle and the gold nucleus is the (electrostatic) Coulomb force and treat each as a single charged particle. Alpha particle Gold nucleus Lightshot