Francis William Aston Biography

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World of Scientific Discovery on Francis William Aston

Aston was born in Harbonne, England, on September 1, 1877. His father was a farmer and metal merchant and his mother, the daughter of a gun-maker. He attended Malvern and Mason's Colleges and spent the years between 1903 and 1908 as a research student in physics at Birmingham University.

Between 1910 and 1919, Aston worked with Joseph J. Thomson at the Cavendish Laboratory at Cambridge University. This period was interrupted by World War I, during which time Aston served as an engineer at the Royal Aircraft Establishment.

Aston's primary field of research was determined early in his career at the Cavendish. In 1912, Thomson was studying the positive rays produced when electrical current is passed through a gas in a glass ("cathode") tube. The effect had first been observed in 1886 by Eugen Goldstein (1850-1930), who called the rays channel rays. Thomson found that, when neon was used in the tube, a pair of positive (or "channel") rays was produced.

Thomson thought that his results meant either that the neon was contaminated with (1) a compound, neon hydride, or (2) a previously unknown element. He set Aston to the task of deciding which of these two explanations--if either--was correct.

Aston's approach was to construct an improved form of Thomson 's cathode tubes. The mass spectrograph he built used electrical and magnetic fields to separate a beam of positive rays into distinct lines, in much the same way that a spectroscope separates white light into colored bands. When neon was analyzed with the mass spectrograph, it produced two clear and distinct lines, one representing an atomic weight of 20 and one a weight of 22.

Aston concluded that neither of Thomson's explanations was correct. Instead, he adopted a concept recently proposed by the English chemist Frederick Soddy. Soddy had demonstrated that the atoms of radioactive elements could exist in two or more forms, all with the same number of protons, but with different masses. He called those forms isotope s.

Aston decided that the two neon lines produced in the spectrograph represented isotopes of neon, with masses of 20 and 22. He suggested designating the isotopes as Ne²⁰ and Ne²².

Aston took his results to mean that Prout's hypothesis was correct. A century earlier, the English chemist William Prout had suggested that all atoms were made of varying numbers of hydrogen atoms. Since the atomic weight of hydrogen is nearly 1, it follows that the atomic weights of all other elements should be integers. When research failed to confirm this conclusion, Prout's hypothesis was rejected.

Now, however, Aston could explain that discrepancy. Any element 's observed atomic weight was the weighted average of all its isotopes. Neon's observed atomic weight of 20.2, for example, reflected the presence of 90 percent neon-20 atoms and 10 percent neon-22 atoms in nature.

In later years, Aston continually improved his mass spectrograph and analyzed most of the known elements. Eventually he identified 212 of the 287 stable isotopes. Aston received the Nobel Prize in chemistry in 1922 for the invention of the mass spectrograph and for the knowledge of isotopes it led to. He was elected a fellow of Trinity College, Cambridge, in 1919 and spent the rest of his life at that institution. He died in Cambridge on November 20, 1945.