Ernest Rutherford

“ The energy of motion of the α-particles is converted into heat. On this view the radium is subject to a fierce and unceasing bombardment by its own particles and is heated by its own radiation. This was confirmed by the work of Rutherford and Barnes in 1903, who showed that three quarters of the heating effect of radium was not directly due to the radium but to its product, the emanation, and that each of the different substances produced in radium gave out heat in proportion to the energy of the α-particles expelled from it. ”

“ If, however, the α-particle carried a charge equal to twice that of the hydrogen atom, the mass of the α-particle would work out at nearly four, i.e. a mass nearly equal to that of the atom of helium.
I suggested that, in all probability, the α-particle was a helium atom which carried two unit charges. On this view, every radioactive substance which emitted α-particles must give rise to helium. This at once offered an explanation of the fact observed by Debierne that actinium as well as radium produced helium. ”

“ In this lecture 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. α-rays were first observed in 1899 as a special type of radiation and during the last six years there has been a persistent attack on this great problem, which has finally yielded to the assault when the resources of the attack seemed almost exhausted. ”

“ In the meantime, further investigation had disclosed that the α-particles produced most of the ionization observed in the neighbourhood of an unscreened radioactive substance, and that most of the energy radiated was in the form of α-rays. It was calculated by Rutherford and McClung in 1901 that one gram of radium radiated a large amount of energy in the form of α-rays. ”

“ The power possessed by the radioactive bodies of apparently spontaneously projecting large masses with enormous velocities supports the view that the atoms of these substances are made up, in part at least, of rapidly rotating or oscillating systems of heavy charged bodies, large compared with the electron. ”

“ THE CHEMICAL NATURE OF THE ALPHA PARTICLES FROM RADIOACTIVE SUBSTANCES ”