Rolling for Rutherford

A local student conducts the Rolling for Rutherford experiment at Sunday’s Fermilab Family Open House. In 1909, Ernest Rutherford conducted an experiment that led him to determine that an atom’s nucleus was a tiny volume compared to the size of the entire atom. He aimed alpha particles (two protons and two neutrons) at a metal foil and observed the patterns made by the recoiling alpha particles. At the open house, children conducted a larger-scale version of this indirect measurement: They determined the radius of a ball by rolling a “probe” ball (Rutherford’s alpha particle) at a row of hidden “target” balls (Rutherford’s metal foil), counting the number of times the probe collides with the target. Inputting their data into the appropriate equation, they got excellent experimental results: The calculated value of the ball’s radius was 1.39 centimeters, with a deviation of a mere 0.7 percent from the measured value of 1.4 centimeters. Photo: Cindy Arnold