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Summary Article: Soddy, Frederick (1877-1956)
From The Hutchinson Dictionary of Scientific Biography

Place: Italy

Subject: biography, chemistry

English chemist who was responsible for major advances in the early developments of radiochemistry, being mainly concerned with radioactive decay and the study of isotopes. For this work he was awarded the 1921 Nobel Prize for Chemistry. He was also a controversial character, holding firm views - with which very few people agreed - about the relationship between science and society.

Soddy was born in Eastbourne, Sussex, on 2 September 1877, the youngest of seven children. He attended Eastbourne College and became much influenced by his chemistry teacher R E Hughes, with whom he published his first scientific paper in 1894 (at the age of only 17). He went to the University College of Wales at Aberystwyth for a year after leaving school, winning an open scholarship to Merton College, Oxford, in 1895. He graduated with top honours three years later; William Ramsay was his external examiner. He spent two years doing research at Oxford, but achieved little of note.

Then in 1900, at the age of 23, he applied for but was refused the professorship of chemistry at the University of Toronto in Canada. He followed this up with a personal visit, which did little to promote his case, and visited Montréal on his way back to the UK. There he was offered a junior demonstrator's post at McGill University, in Ernest Rutherford's department. Soddy accepted and formed a fruitful partnership with Rutherford.

Soddy returned to London in 1902 and worked with Ramsay at University College. In 1904 he went on a brief tour of Australia as an extension lecturer for London University and on his return took up an appointment as a lecturer in physical chemistry at the University of Aberdeen, where he developed the theory of isotopes. In 1914 he was promoted to the chair in chemistry, finally achieving the professorship he had striven for since 1900. During World War I he was involved in research aimed at contributing to the war effort.

Then in 1919 he was appointed Dr Lee's Professor of Chemistry at Oxford, in the hope that he would build up an active research group in the field of radiochemistry. Soddy was instrumental in modernizing the laboratories and active in teaching, but he did little further original research. His interests turned increasingly to political and economic theory and, although he wrote prolifically on these subjects, he was unable to raise the interest or enthusiasm of others, particularly the university authorities. He retired early, in 1936, soon after the death of his wife, which affected him deeply. He travelled in Asia for a while, visiting thorium mines. During and after World War II he became increasingly concerned with how atomic energy was being put to use (as early as 1906 he had realized the tremendous potential in the energy locked up in uranium), and tried to arouse a more active sense of social responsibility among his fellow scientists to halt what he saw as a dangerous trend in the development of human society. He died in Brighton on 22 September 1956.

Soddy's first major scientific contribution, the disintegration law, was the result of his work with Rutherford in Montréal. They postulated that radioactive decay is an atomic or subatomic process, a theory that was immediately accepted. They proposed that there are two radioactive decay series beginning with uranium and thorium and both ending in lead, in which a parent radioactive element breaks down into a daughter element by emitting either an alpha particle or a beta particle. Soon a third series, beginning with actinium, was also demonstrated; it too ends in lead. (A fourth series beginning with neptunium and ending with bismuth was not discovered until after World War II.)

Soddy and Rutherford also predicted that helium should be a decay product of radium, a fact that Soddy and Ramsay proved spectrographically in 1903. In 1911 Soddy published his alpha-ray rule, which states that the emission of an alpha particle from an element results in a reduction of two in the atomic number (Russel's beta-ray rule holds that the emission of a beta particle causes an increase of one in atomic number). The displacement law, introduced by Soddy in 1913, combines these rules and explains the changes in atomic mass and atomic number for all the radioactive intermediates in the decay processes.

Also in 1913 Soddy and Theodore Richards in the USA independently demonstrated the occurrence of different forms of lead in minerals from different sources. These could be added to the plethora of chemically inseparable ‘elements’ that displayed different radioactive properties - there were far more new elements than there were available places in the periodic table. Then Soddy brought order to chaos by proposing that the inseparable elements are in fact identical substances (in the chemical sense), differing only in atomic weight (relative atomic mass) but having the same atomic number. He named the multiple forms isotopes, meaning same place because they occupied the same place in the periodic table. It is now known that all the elements above bismuth (atomic number 83) have at least one radioactive isotope, as do many lighter elements (such as phosphorus). The existence of isotopes also explained anomalies in atomic-weight determinations, which were often found to be caused by the existence of isotopes in elements that were neither radioactive nor formed by radioactive decay.

Soddy was a scientist of great foresight; he predicted the use of isotopes in geological dating and the possibility of harnessing the energy of radioactive nuclei. He was capable of thorough experimentation and dramatic interpretation of the results, having the courage to propose unifying hypotheses. The change in interest that overtook him in middle life was a consequence of what he regarded as the disturbing events that were taking place in the world around him.

© RM, 2018. All rights reserved.

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