Discovery of the positron. This cloud chamber image was taken during the 1932 work by US physicist Carl David Anderson (1905-1991) that led to the discovery of the positron. This particle is the opposite of the electron and the first antimatter particle to be discovered. The image shows the curved track of a positive particle entering the cloud chamber from below. The particle is known to be positive because of the direction in which it bends in the chamber’s magnetic field. The track is too faint to be caused by a proton, and is more like an electron’s track, hence it had to be the predicted positron. These results were published in 1933