How did Ernest Rutherford distinguish alpha rays from beta rays?

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radioactivity Figure 1: Radioactive decay of beryllium-7 to lithium-7 by electron capture (EC; see text).

Ernest Rutherford distinguished between alpha and beta rays by observing their varying abilities to penetrate matter. While investigating uranium radiation, he placed the source near thin foils and discovered that the radiation was more complex than previously assumed.1

He observed that one type of radiation was easily absorbed or blocked by a very thin foil, while another type frequently penetrated the same material. For the sake of simplicity, he named these two types alpha and beta, respectively. It was later determined that the alpha particle is equivalent to the nucleus of a helium atom, whereas the beta particle is identical to an electron or its positive counterpart, the positron.12