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Aston, Francis William

masses mass atomic spectrograph

(1877–1945) British chemical physicist: invented mass spectrograph.

After graduating in chemistry in Birmingham, Aston worked for 3 years as a chemist in a nearby brewery. In his leisure at home he designed and made an improved vacuum pump and in 1903 he turned to physics as a career, working on discharge tubes in Birmingham and, from 1909, in Cambridge as assistant. They worked on the ‘positive rays’ which Thomson had found to be generated within one part of a vacuum tube through which an electric discharge is passed. Aston and Thomson believed that their experiments on positive rays from tubes containing neon gas showed it to contain atoms with masses of about 20 and 22 units. Proof of this, and extension of the work, was interrupted by the First World War.

Aston’s war work at the Royal Aircraft Establishment linked him with a talented group of physicists, including and H Glauert (1892–1934). Soon after the war he devised a mass spectrograph which was able to separate atoms of similar mass and measure these masses accurately (his third spectrograph to 1 in 10 5 ; 1 in 10 9 is now easily available on commercial machines). Aston showed clearly that over 50 elements consisted of atoms of similar but different relative atomic mass (eg for S; 32, 33 and 34) but the same atomic number (ie nuclear charge). The Aston rule is that the masses are approximately integers; the apparent deviations of relative atomic masses of the elements from integers results from the presence of these isotopes.

Aston found that isotopic masses are not exactly integral (by about 1%) and he related the discrepancy (the ‘packing fraction’) to the force binding the nucleus together. Atomic energy generation from nuclear reactions, on Earth or in the stars, can be calculated from packing fractions.

The modern mass spectrograph has played a central part in nuclear physics and radiochemistry, and more recently in exact analysis in organic chemistry. Aston was a ‘one device’ investigator, but he chose a device whose value has been immense.

He was a shy man, a poor teacher, with a passion for sports and for sea travel. He won the Nobel Prize for chemistry in 1922.

Aston, Peter (George) [next] [back] Astaire, Fred (originally Frederick E.Austerlitz Jr.)

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