Francis William Aston

British chemist and physicist (1877–1945)

Aston was born in Harborne, England, the son of a metal merchant. He was educated at Mason College, the forerunner of Birmingham University, where he studied chemistry. From 1898 until 1900 he did research under P. F. Frankland on optical rotation. He left Birmingham in 1900 to work in a Wolverhampton brewery for three years. During this time he continued with scientific research in a home laboratory, where he worked on the production of vacua for x-ray discharge tubes. This work came to the notice of J. H. Poynting of the University of Birmingham who invited Aston to work with him. He remained at Birmingham until 1910 when he moved to Cambridge as research assistant to J. J. Thomson. He became a research fellow at Cambridge in 1920 and stayed there for the rest of his life, apart from the war years spent at the Royal Aircraft Establishment, Farnborough. Aston's main work, for which he received the Nobel Prize for chemistry in 1922, was on the design and use of the mass spectrograph, which was used to clear up several outstanding problems and became one of the basic tools of the new atomic physics.

Thomson had invented an earlier form of spectrograph in which a beam of positive rays from a discharge tube passed through a magnetic and an electric field, which deflected the beam both horizontally and vertically. All particles (ions) with the same mass fell onto a fluorescent screen in a parabola. Aston improved the design by using a suitable magnetic field, so that ions of the same mass were focused in a straight line rather than a parabola. Different ions were deflected by different amounts, and the spectrograph produced a photographic record of a series of lines, each corresponding to one type of ion. The deflections allowed accurate calculation of the mass of the ions.

Aston's first spectrograph was ready in 1919 and with it he was soon able to throw light on one outstanding problem about the nature of the elements. In 1816 William Prout had put forward his hypothesis that all elements are built up from the hydrogen atom and that their atomic weights are integral multiples of that of hydrogen. Although receiving considerable support it was eventually rejected when it was found that many elements have non-integral weights (e.g. chlorine: 35.453). Frederick Soddy in 1913 had introduced the idea of isotopes; that is, the same chemical element in different forms having differing weights. Aston established that isotopes are not restricted to radioactive elements but are common throughout the periodic table. He also saw that they could explain Prout's hypothesis. Thus he found that neon was made from the two isotopes ²⁰Ne and ²²Ne in the proportion of 10 to 1. This will give a weighted average of 20.2 for a large number of neon atoms. The value of 35.453 for chlorine can be similarly explained. The whole-number rule is his principle that atoms have a mass that is equivalent to a whole number of hydrogen atoms.

Aston then went on to determine as many atomic weights as accurately as his instruments would allow. His first spectrograph was only suitable for gases but by 1927 he had introduced a new model capable of dealing with solids. From 1927 to 1935 he resurveyed the atomic weights of the elements with his new instrument.

In the course of this activity he found some minor discrepancies with the whole-number rule. Thus the atomic weight of hydrogen is given not as 1 but 1.008, of oxygen–16 as 15.9949 and of oxygen–17 as 16.99913. Aston attempted to show why these values are so tantalizingly close to the integral values of Prout – why the isotopes of oxygen are not simple 16 and 17 times as massive as the hydrogen atom. He argued that the missing mass is in fact, by the mass–energy equivalence of Einstein, not really missing but present as the binding energy of the nucleus. By dividing the missing mass by the mass number and multiplying by 10,000, Aston went on to calculate what was later called the ‘packing fraction’ and is a measure of the stability of the atom and the amount of energy required to break up or transform the nucleus.

Thus, contained in Aston's work were the implications of atomic energy and destruction and he believed in the possibility of using nuclear energy – he also warned of the dangers. He lived just long enough to see the dropping of the first atomic bomb in August 1945.

The British chemist and physicist Francis William Aston (1877-1945) invented the mass spectrograph and discovered the isotopic complexity of the elements.

Francis Aston was born on Sept. 1, 1877, at Harborne, Birmingham, where his father was a metal merchant and ran a small farm. He studied chemistry at Mason College (which later became the University of Birmingham). In his spare time he trained himself in the various arts of apparatus construction, especially glassblowing. When his scholarship expired, he took a post with a brewery firm. After 3 years he returned to the University of Birmingham. In 1910 an invitation arrived from J. J. Thomson to join him at the Cavendish Laboratory, Cambridge.

Separation of the Isotopes

Thomson was examining positive "rays" produced in electric-discharge tubes at low pressure. These were in fact atoms stripped of some or all of their outer electrons and thus carried an overall positive charge. Thomson had obtained parabolic tracks by submitting the rays to the simultaneous application of magnetic and electrostatic fields. With Aston's help he discovered that neon gas had a small component that gave a separate parabolic track. Since each parabola was characterized by a unique mass-charge ratio, deductions concerning particle masses could be made, and it was concluded that the atomic masses of the major and minor components of neon were 20 and 22 respectively.

Aston then attempted to separate the two components by physical means and to measure their densities on a quartz microbalance of his own devising. In 1913 he achieved a partial separation by submitting the gas to repeated diffusions through pipe clay; small, but significant, differences in gas density were found for the two samples obtained.

Mass Spectrograph

Gradually, the concept of isotopes was becoming clearer and more generally accepted, and in 1919 Aston worked out some ideas on a new instrument which could give results indicative of mass alone. Unlike Thomson's apparatus, Aston's invention employed magnetic and electrostatic fields producing opposite deflections in the same plane. By focusing the beams through fine slits, Aston obtained a series of lines, each of which corresponded to a definite particle mass. The series of lines was a mass spectrum, and the original instrument was the first mass spectrograph.

With this equipment Aston began an examination of the isotopic composition of more than 50 elements. In those cases where neither the element nor any of its available compounds were volatile, he utilized a solid product containing the element as the anode of his discharge tube. In almost every case the isotopic mass was a whole number within the limits of experimental accuracy (1 in 1000). The only notable exception was hydrogen, 1.008. Thus isotopy was not a rare phenomenon, as some workers had supposed, but widespread and affecting most elements. Aston was led by these integral isotopic weights to conclude that all nuclei are composed of protons (of unit weight) and of negligibly light electrons.

The importance of precise values for the isotopic masses led Aston to design an improved mass spectrograph in 1925, with an accuracy of 1 in 10,000. A later instrument (1927) gave an accuracy improved by a factor of 10. With this refined apparatus he discovered a great many new isotopes, often present in only very small amounts in the natural element.

Assessment of His Work

Many important consequences flowed from Aston's work on the mass spectrograph. As he himself recognized, the fractional isotopic weight of hydrogen implied that if it were converted to helium substantial amounts of the mass would be converted into energy. Using Albert Einstein's relativity relationship, Aston predicted that the energy liberated in a nuclear reaction of this kind would be enormous. His opinions were justified when the first atomic bomb was exploded a few months before his death.

The more immediate importance of the mass spectrograph was its ability to give data on nuclear masses with great precision, thus laying the foundations of the atomic energy industry. More recently, the mass spectrometer has proved an indispensable tool for structural investigations in organic chemistry.

The importance of Aston's work was quickly recognized, and in 1921 he was elected a fellow of the Royal Society. The following year he received the Nobel Prize in chemistry. His authoritative book Isotopes first appeared in 1922 and was followed by many other editions up to 1941. His other book, Mass Spectra and Isotopes, appeared in 1933.

Other Interests

In addition to his work at the Cavendish Laboratory, Aston made some valuable scientific contributions to the study of astronomical eclipses. In 1925 he photographed the sun's corona from Sumatra. He made expeditions to study the solar eclipses of 1932 and 1936 in Canada and Japan respectively, though clouds prevented direct observations. However, Aston was able to study the polarization of the light in the neighborhood of the eclipsed sun.

Aston never married. He was often accompanied on his travels by his sister, Helen, to whom he was deeply devoted. He died at Trinity College, Cambridge, on Nov. 20, 1945.

Further Reading

There is no full-length biography of Aston. Edvard Farber, ed., Great Chemists (1961), contains a short biography, and an old but still useful source, Bernard Jaffe, Crucibles: The Lives and Achievements of the Great Chemists (1932), offers an adequate account of Aston's life and work. The Nobel Foundation's Nobel Lectures, Including Presentation Speeches and Laureates' Biographies: Chemistry, 1922-1941 (1967) contains a brief biography and a résumé of the work for which Aston received the prize. F. J. Moore, A History of Chemistry, revision prepared by William T. Hall (1939), includes a brief sketch of Aston and places his work in historical perspective.

Aston, W[illiam] G[eorge] (1841-1911), philologist, born in Derry and educated at QUB. He wrote grammars of Japanese, a translation of the chronicles of Japan (Nohongi, 1896) and studies of Japanese culture, A History of Japanese Literature (1899) and Shinto, the Way of the Gods (1905).

Francis William Aston
Born	1 September 1877(1877-09-01) Harborne, Birmingham
Died	20 November 1945 (aged 68) Cambridge
Nationality	United Kingdom
Fields	Chemistry, physics
Institutions	University of Cambridge
Alma mater	University of Birmingham University of Cambridge
Doctoral advisor	J. J. Thomson
Known for	Mass spectrograph Whole Number Rule
Notable awards	Nobel Prize for Chemistry (1922)

Francis William Aston (1 September 1877 – 20 November 1945) was a British chemist and physicist who won the 1922 Nobel Prize in Chemistry "for his discovery, by means of his mass spectrograph, of isotopes, in a large number of non-radioactive elements, and for his enunciation of the whole-number rule."^[1][2]

Contents 1 Early life 2 Research 3 Private life 4 Notes 5 External links

Early life

Francis Aston was born in Harborne, now part of Greater Birmingham, on 1 September 1877. He was the third child and second son of William Aston and Fanny Charlotte Hollis. He was educated at the Harborne Vicarage School and later Malvern College in Worcestershire where he was a boarder. In 1893 Francis William Aston began his university studies at Mason College (later part of the University of Birmingham) where he was taught physics by John Henry Poynting and chemistry by Frankland and Tilden. From 1896 on he conducted additional research on organic chemistry in a private laboratory at his father’s house. In 1898 he started as a student of Frankland financed by a Forster Scholarship; his work concerned optical properties of tartaric acid compounds. He started to work on fermentation chemistry at the school of brewing in Birmingham and was employed by W. Butler & Co. Brewery in 1900. This period of employment ended in 1903 when he returned to the University of Birmingham under Poynting as an Associate.

Research

With a scholarship from the University of Birmingham he pursued research in physics following the discovery of X-rays and radioactivity in the mid-1890s. Aston studied the current through an electronic discharge tube (a gas-filled tube with electrodes under high vacuum). The research, conducted with self-made discharge tubes, led him to investigate the volume of the Crookes dark space now known as Aston dark space.^[3][4][5]

After the death of his father, and a trip around the world in 1908, he was appointed lecturer at the University of Birmingham in 1909 but moved to the Cavendish Laboratory in Cambridge on the invitation of J. J. Thomson in 1910.

Joseph John Thomson revealed the nature of the cathode ray and then discovered the electron and he was now doing research on the positively charged "Kanalstrahlen" discovered by Eugen Goldstein in 1886. The method of deflecting particles in the "Kanalstrahlen" by magnetic fields, discovered by Wilhelm Wien in 1908, and electric fields were used to separate the different ions by their charge and mass. The first sector field mass spectrometer was the result of these experiments. The ions followed a parabolic flight path and were recorded on photographic plates from which their exact mass could be determined by the mass spectrometer.

It was speculations about isotopy that directly gave rise to the building of a mass spectrometer capable of separating the isotopes of the chemical elements. Aston initially worked on the identification of isotopes of the element neon and later chlorine and mercury. First World War stalled and delayed his research on providing experimental proof for the existence of isotopes by mass spectroscopy and during the war Aston worked at the Royal Airforce Establishment in Farnborough as a Technical Assistant working on aeronautical coatings.

After the war he returned to research at the Cavendish Laboratory in Cambridge, and completed building his first mass spectrograph (now mass spectrometer) that he reported on 1919. Subsequent improvements in the instrument led to the development of a second and third instrument of improved mass resolving power and mass accuracy. These instruments employing electromagnetic focusing allowed him to identify 212 naturally occurring isotopes. In 1921, Aston became a fellow of the Royal Society and received the Nobel Prize in Chemistry the following year.

His work on isotopes also led to his formulation of the Whole Number Rule which states that "the mass of the oxygen isotope being defined [as 16], all the other isotopes have masses that are very nearly whole numbers," a rule that was used extensively in the development of nuclear energy. The exact mass of many isotopes was measured leading to the result that hydrogen has a 1% higher mass than expected by the average mass of the other elements. Aston speculated about the subatomic energy and the use of it in 1936.

Isotopes^[6] and Mass-spectra and Isotopes^[7] are his most well-known books.

Private life

In his private life he was a sportsman, cross-country skiing and skating in winter time, during his regular visits to Switzerland and Norway; deprived of these winter sports during the First World War he started climbing. Between the ages of 20 and 25 he spent a large scale of his spare time cycling. The new invention of motorized vehicles he constructed a combustion engine of his own in 1902 and participated in the Gordon Bennett Race in Ireland in 1903. Not content with these sports he also engaged in swimming, golf, especially with Rutherford and other colleagues in Cambridge,^[8] tennis, winning some prizes at open tournaments in England Wales and Ireland and learning surfing in Honululu in 1909. Coming from a musical family, he was capable of playing the piano, violin and cello at a level such that he regularly played in concerts at Cambridge. He visited many places around the globe on extensive travel tours starting from 1908 when he visited and ending with a trip to Australia and New Zealand in 1938-1939.^[9][10]

Aston was a skilled photographer and interested in astronomy. He joined several expeditions to study solar eclipses in Benkoeben in 1925, Sumatra in 1932, Memphri in Canada in 1936 and Kamishri in Japan. He also planned to attend expeditions to South Africa in 1940 and Brazil in 1945 in later life. Aston died in Cambridge on 20 November 1945.

The lunar crater Aston was named in his honour.

Notes

1. ^ "The Nobel Prize in Chemistry 1922". Nobel Foundation. http://nobelprize.org/nobel_prizes/chemistry/laureates/1922/. Retrieved 2008-04-14. 
2. ^ Squires, Gordon (1998). "Francis Aston and the mass spectrograph". Dalton Transactions: 3893–3900. doi:10.1039/a804629h. http://www.rsc.org/publishing/journals/DT/article.asp?doi=a804629h. Retrieved 2007-12-06. 
3. ^ Francis William Aston (1907). "Experiments on a New Cathode Dark Space in Helium and Hydrogen". Proceedings of the Royal Society of London. Series A 80 (535): 45–49. doi:10.1098/rspa.1907.0072. http://links.jstor.org/sici?sici=0950-1207%2819071209%2980%3A535%3C45%3AEOANCD%3E2.0.CO%3B2-1. 
4. ^ Francis William Aston (1907). "Experiments on the Length of the Cathode Dark Space with Varying Current Densities and Pressures in Different Gases". Proceedings of the Royal Society of London. Series 79 (528): 80–95. doi:10.1098/rspa.1907.0016. http://links.jstor.org/sici?sici=0950-1207%2819070424%2979%3A528%3C80%3AEOTLOT%3E2.0.CO%3B2-Z. 
5. ^ Francis William Aston (1911). "The Distribution of Electric Force in the Crookes Dark Space". Proceedings of the Royal Society of London. Series A 84 (573): 526–535. doi:10.1098/rspa.1911.0005. http://links.jstor.org/sici?sici=0950-1207%2819110126%2984%3A573%3C526%3ATDOEFI%3E2.0.CO%3B2-N. 
6. ^ Aston, Francis William (1922). Isotopes. London: E. Arnold. pp. 152. 
7. ^ Aston, Francis William (1933). Mass-Spectra and Isotopes. London: Edward Arnold. 
8. ^ KM Downard (2007). "Cavendish's Crocodile and Dark Horse - The Lives of Rutherford and Aston in Parallel". Mass Spectrometry Reviews 26 (5): 713–723. doi:10.1002/mas.20145. 
9. ^ George de Hevesy (1948). "Francis William Aston. 1877-1945". Obituary Notices of Fellows of the Royal Society 5 (16): 634–650. http://links.jstor.org/sici?sici=1479-571X%28194805%295%3A16%3C634%3AFWA1%3E2.0.CO%3B2-H. 
10. ^ KM Downard (2007). "Francis William Aston - the man behind the mass spectrograph". European Journal of Mass Spectrometry 13 (3): 177–190. doi:10.1255/ejms.878. 

External links

• Annotated bibliography for Francis Aston from the Alsos Digital Library for Nuclear Issues
• Aston biography from Nobel Prize site
• Aston biography from Cambridge

v • d • e Nobel Laureates in Chemistry Jacobus van 't Hoff (1901) · Emil Fischer (1902) · Svante Arrhenius (1903) · William Ramsay (1904) · Adolf von Baeyer (1905) · Henri Moissan (1906) · Eduard Buchner (1907) · Ernest Rutherford (1908) · Wilhelm Ostwald (1909) · Otto Wallach (1910) · Marie Curie (1911) · Victor Grignard / Paul Sabatier (1912) · Alfred Werner (1913) · Theodore Richards (1914) · Richard Willstätter (1915) · Fritz Haber (1918) · Walther Nernst (1920) · Frederick Soddy (1921) · Francis Aston (1922) · Fritz Pregl (1923) · Richard Zsigmondy (1925) Complete roster · 1901–1925 · 1926–1950 · 1951–1975 · 1976–2000 · 2001–present

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