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THE MASS SPECTROGRAPH
6. Neon Problems

Francis William Aston

"There is scarcely a research in nuclear physics which does not use his work, directly or indirectly, and usually many times over." - G.P. Thomson

On 1st September 1877 Francis William Aston was born at Harborne, a few miles from Birmingham. He was the third child in a family of seven, and enjoyed playing with mechanical toys in his youth.

Aston was first educated at Harborne Vicarage School, but began to study science at Malvern College, where he demonstrated his ability in chemistry, physics and mathematics. Aston was at Malvern for two years before entering Mason College, Birmingham, in 1893.

At Mason College, Aston was taught chemistry by Tilden and Frankland, and physics by Poynting. In 1898 he was awarded the Forster Scholarship and worked in collaboration with Frankland to publish his first paper in 1901.

For financial reasons Aston left the college and began working as a fermentation chemist at a brewery in Wolverhampton, where he stayed for three years. In 1903 Aston decided to return to the college, which had now become the University of Birmingham. With Röntgen's recent discovery of X-rays, Aston's interests had turned to physics, and he began studying the properties of gas discharges.

In 1908 Aston's father died, leaving Aston enough money to travel around the world. The following year Professor J.J. Thomson invited Aston to move to the Cavendish Laboratory and work as Thomson's assistant. Aston had been recommended to Thomson by his former teacher Poynting, and was happy to accept the Cambridge post which would leave him more time for research. Since his discovery of the electron Thomson had been analysing positive rays, and had developed a method of measuring atomic weights by using combinations of magnetics and electric fields to produce curves on a photographic plate. Aston helped to further refine these experiments.

Thomson and Aston found an unexpected effect when they investigated the element neon. Instead of showing only one curve on the photograph, it showed two, suggesting that the element was made up of two different types of atoms which were chemically identical but of different mass, named isotopes. This interested Aston, and he devoted the rest of his career to developing the mass spectrograph capable of accurately measuring these chemical isotopes.

Aston's work was interrupted by the First World War, when he worked as a chemist at Farnborough in the Royal Aircraft Factory, investigating the canvas used to cover aeroplanes. In 1914 he crashed in an experimental aeroplane, but escaped unhurt. He lived in a civilian mess with other scientists including Frederick Lindemann and J.J.'s son George Thomson. Lindemann was sceptical of Aston's isotope hypothesis, but Aston's opinion wouldn't be swayed and he enjoyed this opportunity to discuss his ideas with close friends.

After the war Aston returned to the problem of the neon isotopes, and constructed his first mass spectrograph. The apparatus clearly showed the two types of neon, and also showed isotopes for chlorine and many other elements. It was an almost immediate success, and Aston received quick acclaim. He was elected a fellow of Trinity College, Cambridge, in 1920, and lived there for the rest of his life. The following year he was elected to the Royal Society, and in 1922 he won the Nobel Prize for Chemistry in 1922.

Aston continued to improve his mass spectrograph, and succeeded in analysing most of the chemical elements. In all but a few cases he made the first isotopic analysis. His first spectrograph had established the 'whole number rule', that the masses of all elements except hydrogen are a whole number of atomic mass units. The improved accuracy of his second spectrographs measured the differences from this rule, which gave details of the forces holding atoms together. Aston's third and final mass spectrograph had an accuracy of 1 in 100,000.

In later years other scientists began building mass spectrographs, but there 'are few instances in modern science in which the first discoverer of a major field of research has had it his own way for such a long time'. Modern spectrographs have an accuracy of about 1 in a billion.

Aston had many interests outside his work. He enjoyed sport, especially winter sports, and was an enthusiastic skier and rock climber. He would take annual visits to Switzerland and Norway for long skiing exhibitions, until he began to suffer from a heart condition in late 1934. He played tennis at tournament class, and golf in a famous foursome with the other Cavendish physicists Ernest Rutherford, Ralph Fowler and G.I. Taylor.

Aston combined his love of sport with a love of travelling. He once cycled two hundred miles in a single day. He considered 'surf-riding', which he learnt in Honolulu, to by the finest sport in the world. He would combine this love of travelling with his scientific work, and would often go on expeditions to see eclipses around the world. He was also musical and could play the cello, piano or violin.

Aston enjoyed life and was interested in the world. He was precise and conservative, but could accept new ideas with great relish. He gave good occasional lectures but didn't teach, as it took too much time away from his research.

Aston published many papers and wrote his book 'Isotopes' in 1922, later reprinted as 'Mass Spectra and Isotopes'. As well as his Nobel prize he won the Hughes and the Royal Medals from the Royal Society, and was given honorary degrees by Birmingham and Dublin.

Aston never married and lived in Trinity College for thirty-five years, until he died on 20th November 1945.

Read a biography of Aston at the Nobel e-museum:
www.nobel.se/chemistry/laureates/1922/aston-bio.html

Reference:
'Dr. Francis William Aston, F.R.S.', G.P. Thomson, Nature 157, 290 (1946)
'Francis Aston and the mass spectrograph', Gordon Squires, Dalton Transactions 23, 3893 (1998)