Frederick Soddy (1877 – 1956) and the Law of Radioactive Decay

  August 10, 2021   Read time 3 min
Frederick Soddy (1877 – 1956) and the Law of Radioactive Decay
The British chemist Frederick Soddy collaborated with Ernest Rutherford (1871–1937) to discover the law of radioactive decay and then independently developed the concept of the isotope. Soddy was born on September 2, 1877, at Eastbourne, Sussex, England.

He received his early professional education at Eastbourne College and the University of Wales, Aberystwyth. In 1895, Soddy won a scholarship to the Merton College of Oxford University. He graduated from that institution in 1898 with first honors in chemistry. After two years of generally routine postgraduate research at Oxford University, he traveled to Canada and worked as a demonstrator in the chemistry department from 1900 to 1902 at McGill University, Montreal. By good fortune, Soddy came in contact with Rutherford, who was at McGill conducting research on the newly discovered phenomenon of radioactivity. They collaborated on a series of important papers in which they introduced the theory of radioactive decay— a scientific principle of great importance in nuclear technology. They also performed an early investigation of the gaseous emanation of radium.

By 1903, Soddy had left Canada, returned to England, and found a position working with the Scottish chemist Sir William Ramsay (1852–1916) at University College in London. Soddy and Ramsay used spectroscopic techniques to demonstrate that the element helium was being released during the radioactive decay of radium. This result made an important connection—namely, that alpha particles emitted during the radioactive decay of radium (and other heavy nuclei) are really helium nuclei.

From 1904 to 1914, Soddy was a lecturer in physical chemistry and radioactivity at the University of Glasgow, Scotland. In this period, Soddy made his greatest contributions to nuclear technology. In particular, he evolved the so-called Displacement Law by suggesting that the emission of an alpha particle from an element causes that element to move back (or “displace itself”) two places in the periodic table. Pursuing this line of thinking further, Soddy reached his intellectual peak in 1913 when he proposed the concept of the isotope, using this word (derived from ancient Greek and meaning “same place”) for the first time in the February 28 issue of Chemical News. In a brilliant integration of available experimental data on radioactivity, he postulated that certain elements exist in two or more forms that have different atomic weights but nearly indistinguishable chemical characteristics.

Soddy’s work allowed scientists to unravel the bewildering variety of “new” radioactive elements, such as mesothorium 1 (MsTh1; actually, the radioisotope radium-228 within the thorium decay series) and radioactinium (RdAc; the radioisotope thorium-227 within the actinium decay series), which had been discovered during the previous decade. The isotope concept made things fit together a bit more logically on the periodic table. Soddy’s work also prepared the scientific community for Rutherford’s identification of the proton and his speculation about the possible existence of a neutron in 1919. However, the isotope hypothesis only became completely appreciated when James Chadwick (1891–1974) discovered the neutron in 1932.

In 1914, Soddy received an appointment as professor of chemistry at the University of Aberdeen, Scotland. He turned his attentions away from radioactivity and conducted chemical research in support of the British war effort during World War I. Beyond this point in his career, Soddy never contributed significantly to the field of nuclear technology. In 1919, he left Aberdeen to become a professor of chemistry at Oxford University. He remained in that position until 1937, when he retired following the sudden death of his wife due to a heart attack.

Soddy received the 1921 Nobel Prize in chemistry for his “investigations into the origin and nature of isotopes.” Although he had made some excellent contributions to nuclear technology between 1900 and 1914, once he left the University of Glasgow, he basically abandoned any further technical contributions to the field. Soddy attempted, instead, to use his status as a Nobel laureate to champion a variety of social and political causes, but his point of view on such volatile topics as Irish autonomy and women’s rights did not gain general acceptance. After his retirement from Oxford University, he continued to write on social and economic issues and remained generally favorable regarding the use of nuclear energy. Soddy died on September 22, 1956, in Brighton, England.