Ernest Rutherford, for example, a young New Zealander studying under J. J. Thomson at the Cavendish Laboratory in Cambridge, discovered through experiments with uranium that uranic rays were of two distinct types. The ones he dubbed “alpha rays” played the primary role in ionizing gases, but they did not travel far and could be blocked altogether by a sheet of paper. The “beta rays,” on the other hand, ionized only weakly but were extremely penetrating. They could pass through metal screens and cover considerable distances. Adherents of the new science had also learned that radioactivity was
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