Detection of High-Angle Alpha Particle Scattering through Gold Foil

In the beginning of the 20th century, physicists had begun to determine the structure of atoms. J.J. Thomson had discovered the presence of electrons negatively charged particles with a mass much less than the overall mass of the electron using cathode rays[1]. Thomson further hypothesized that the full structure of the atom consisted of electrons surrounded by a ”soup” of positive charge. This structure predicts small deflections during scattering events, detailed further in Section II. This behavior was tested by Ernest Rutherford, and experimental results were shown to disagree with Thomson’s predictions. To reflect newfound results, Rutherford proposed a new model of the atom, the Rutherford model, which consisted of a densely-packed positive charge (now known as a nucleus) in the center. This refutal of Thomson’s ”plum pudding” model in favor of this alternative theory was a crucial step in the progress towards our modern day understanding of the atom. In this experiment, we measure the scattering of α particles emitted from an Am 241 source through gold foil. Through geometric considerations and calibration procedures, we determine the data trends that both the Rutherford and Thomson theories predict for our measurements. Finally, by comparing the two predictions to our experimental data, we conclude that Rutherford scattering is able to successfully describe our data.