Ernest Rutherford - Scientific Research

Scientific Research

During the investigation of radioactivity he coined the terms alpha ray and beta ray in 1899 to describe the two distinct types of radiation emitted by thorium and uranium. These rays were differentiated on the basis of penetrating power. From 1900 to 1903 he was joined at McGill by the young Frederick Soddy (Nobel Prize in Chemistry, 1921) and they collaborated on research into the transmutation of elements. Rutherford and Soddy demonstrated that radioactivity was often the spontaneous disintegration of atoms into other types of atoms (one element spontaneously being changed to another). This would suggest that radioactivity was a nuclear phenomenon, but the nucleus of the atom was not then known (Rutherford himself would later deduce it in 1911).

While studying radioactivity, he noticed that a sample of radioactive material invariably took the same amount of time for half the sample to decay—its "half-life"—and created a practical application using this constant rate of decay as a clock, which could then be used to help determine the age of the Earth, which turned out to be much older than most of the scientists at the time believed.

In 1903, Rutherford considered a type of radiation discovered (but not named) by French chemist Paul Villard in 1900, as an emission from radium, and realised that this observation must represent something different from his own alpha rays and beta rays, due to its very much greater penetrating power. Rutherford therefore gave this third type of radiation the name of gamma ray, which was retained by the scientific community. All three of Rutherford's terms are in standard use today (other types of radioactive decay have since been discovered, but Rutherford's three types are among the most common).

In Manchester, he continued to work with alpha radiation. In conjunction with Hans Geiger, he developed zinc sulfide scintillation screens and ionisation chambers to count alphas. By dividing the total charge they produced by the number counted, Rutherford decided that the charge on the alpha was two. In late 1907, Ernest Rutherford and Thomas Royds allowed alphas to penetrate a very thin window into an evacuated tube. As they sparked the tube into discharge, the spectrum obtained from it changed, as the alphas accumulated in the tube. Eventually, the clear spectrum of helium gas appeared, proving that alphas were at least ionised helium atoms, and probably helium nuclei.