The Chemical Nature of the Alpha Particles from Radioactive Substances

The text is a Nobel lecture by Ernest Rutherford, dated December 11, 1908, on the chemical nature of the alpha particles from radioactive substances. The lecture says that an attempt will be made to give a brief historical account of the development of our knowledge of the α-rays, and to trace the long and arduous path trodden by the experimenter in the attempts to solve the difficult question of the chemical nature of the α-particles.

The lecture quotes the conclusion that the uranium radiation is complex and that at least two distinct types of radiation are present. The lecture says that Bragg showed that the α-particle, on account of its great energy of motion, was not deflected from its path, but travelled in nearly a straight line, ionizing the molecules in its path. The lecture calls it remarkable that a chemically inert element like helium should play such a prominent part in the constitution of the atomic systems of uranium and thorium and radium.