Alpha particles:
1898 Rutherford showed there was more than one type of radiation (alpha and beta). Read a biography of Rutherford.
1899 Several experimenters showed that the two radiations could be deviated by magnetic field.
1900 P.Curie found a component of the radiation which was not deflected by magnetic fields.
1900 Villard showed that this non-deviable component had very long range; he had identified gamma rays.
1900-02 Soddy and Rutherford showed that radiation was atomic disintegration producing new kinds of matter.
1903-04 Soddy and Ramsay studied radium emanations and showed that helium was produced.
1903 Rutherford's experiments on alpha rays, deflecting them with magnetic and electric fields. He found they were positive particles, found that their charge/mass ratio was half that of a hydrogen ion. Read "Alpha as a Particle..."
1908 Rutherford and Geiger found that the actual charge of an alpha particle was twice the charge of an electron.
1908 Rutherford and Royds showed that alpha particles had the same absorption spectrum as helium gas.
Beta particles:
1900 Becquerel deflected beta-rays with a magnetic field and showed they were negative.
1900 The Curies used an electrometer to show that beta-rays were negative.
1900 Becquerel showed deflection of beta-rays by electric fields; they had a range of velocities, but he was able to calculate an average velocity and estimate their charge/mass ratio.
1902 Kaufmann tried measuring charge/mass with combined electric and magnetic fields.
1909 Bucherer, with more precise measurements, concluded that the beta-particle was a fast-moving electron.
Gamma rays:
1906 Rontgen's discovery and study of X-rays, followed over the next few years by various studies of methods of detecting X-rays by Rontgen, Thomson, Rutherford, Geiger... Rontgen won the first ever Nobel prize for Physics in 1901
1913 von Laue of the University of Munich, and his students - W.Friedrich and P.Knipping,were able to demonstrate diffraction (like light) of X-rays when they were passed through crystals. Their experiments demonstrated the wave nature of X-rays and the regular structure of atoms within crystals.VonLaue won the 1914 Nobel prize for Physics.
Around these years, gamma rays were shown to have the same properties as X-rays.
The last section of this article describes the discovery of all three kinds of rays.
So by now radioactive emanations were known to be of three kinds - positive particles with characteristics like helium, negative particles that behaved like electrons, and a radiation similar to X-rays.
