The proton was discovered by Ernest Rutherford through the gold foil experiment, says the Purdue University College of Science. The results of the experiment led Rutherford to conclude that the positive charge and the mass of an atom are concentrated in a tiny fraction of the overall volume. In 1920, Rutherford proposed that the positively charged particle in an atom’s nucleus be called a proton.
The Purdue University College of Science notes that after the discovery of radioactivity, Rutherford began to study the alpha particles emitted by uranium metal and its compounds. Rutherford discovered that a narrow beam of alpha particles broadened as it passed through a thin film of mica or metal. When the foil was bombarded with alpha particles, Geiger, who was Rutherford’s assistant, found that there was a tiny scattering on the order of one degree.
The results of the study were the same as Rutherford’s expectations. He was able to confirm that the alpha particle had a significant mass and moved very quickly. He expected that the alpha particles would pass through the metal foil just like how a rifle bullet would penetrate a bag of sand. Eventually, Rutherford concluded that the positive charge and the atom’s mass were concentrated in a small fraction of the total volume. In 1911, he published the results and also presented a model for the structure of the atom that includes the proton, according to the Purdue University College of Science.