Francis W. Aston was an English chemist and physicist whose motto--"Make more, more, and yet more measurements"--summed up the hard work and dedication he brought to a lifetime of achievement. Among his most important contributions were detailed observations of atomic phenomena with a mass spectrograph that he built himself. This device allowed him to articulate the theory that the atomic weight of each element is a whole number, but that most elements have isotopes (atoms of the same element with the same number of protons in their nucleus, but different numbers of neutrons). For these insights he received the 1922 Nobel Prize in chemistry. From evidence he gathered in the 1920s, Aston went on to note that the weights of atoms vary minutely from whole numbers in proportion to the density of their nuclei.
Francis William Aston was born on September 1, 1877, in Harborne, Birmingham, England, the third of seven children. His parents were William Aston, farmer and metal merchant, and Fanny Charlotte Hollis Aston, the daughter of a gunmaker. From an early age Aston showed great scientific curiosity, performing experiments in his makeshift laboratory on the family farm. In 1893 he graduated from high school at the top of his class in math and science. While at Mason College (which became the University of Birmingham), he worked with P. F. Frankland in organic chemistry and optics, issuing a paper in 1901 on his results. Lacking scholarship money for continued studies, he went to work for a brewing company as resident chemist in the early 1900s. He also performed experiments in electricity with sophisticated devices he built at home.
For this work he was awarded a scholarship in 1903 to the new University of Birmingham. There he discovered a phenomenon, now called the Aston space, that appears in electrical currents passed through gases at low pressures. In 1910, working with Joseph John Thomson both at Cambridge University and the Royal Institution in London, he began experiments on the gas neon. When his work was interrupted by World War I, Aston returned to Cambridge. In 1919 he became a fellow of Trinity College, Cambridge, where he stayed for the rest of his life. That same year he managed to perfect the mass spectrograph. In this instrument, a beam of neon atoms directed onto a photographic plate angled away from the flow of atoms created a distinctive pattern when the heavier atoms deflected farther down the plate than the lighter atoms. Taking the average of these deflections, Aston was able to calculate the proportion of heavier to lighter atoms in the element neon. From this information Aston deduced that most elements are mixtures of isotopes and that the weights of atoms are always whole numbers (the whole number rule). He posited that isotopic constituents accounted for the fractional weights observed for some atoms.
Not one to rest on his 1922 Nobel Prize laurels, Aston built larger and even more accurate spectrographs. From a new round of observations taken with one of these instruments in 1927, Aston measured fractional deviations from the whole number rule. He discovered that the tighter the packing of the particles in an atomic nucleus, the greater a fraction of its mass became converted to energy devoted to keeping the nucleus together. He incorporated these "packing fractions " into calculations from which physicists and chemists have derived essential information about the abundance and stability of the elements.
Politically conservative, Aston preferred working alone to collaborating with colleagues. He never married, preferring to keep busy with outdoor sports, traveling by sea and becoming an accomplished photographer and amateur musician. He also loved animals. Aston acquired some financial skills, leaving behind a large estate to Trinity College and various scientific enterprises. He held many honorary degrees and received, in addition to the Nobel Prize, awards such as the 1938 Royal Medal of the Royal Society, of which he was a member, and the 1941 Duddell Medal and Prize of the Institute of Physics. He died on November 20, 1945, in Cambridge.
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