In the Rutherford Gold Foil experiment, alpha particles (with a charge of 2e and a mass of 6.645x10-27 kg) were shot directly at a thin sheet of gold with a speed of 9.290x106 m/s from very far away. They found that most of the time the alpha particles traveled straight through the thin sheet, but sometimes they would bounce directly back. The alpha particle would only bounce back when its path was aimed directly at a gold nucleus (otherwise it would pass through the empty space between nuclei). This is actually how we discovered the gold nucleus has 79 protons centered in the middle of the atom (rather than spread out even through the atom). What is the closest distance that this alpha particle could get before bouncing back?