Ernest Rutherford

British physicist

• Born: August 30, 1871; Nelson, New Zealand
• Died: October 19, 1937; Cambridge, England

British physicist Ernest Rutherford is known as the father of nuclear physics. His experiments with radiation, description of the structure of the atom, and initial success at artificially splitting the atom laid the foundation for nuclear weapons and power generation.

Primary field: Physics

Specialties: Atomic and molecular physics; nuclear physics; radiochemistry

Early Life

Ernest Rutherford was born on August 30, 1871, in Nelson, New Zealand, one of twelve children. His grandfather moved to rural New Zealand from Scotland in 1843, and Rutherford’s father, James Rutherford, worked as a wheelwright and farmer. His mother, Martha Thompson, was a school teacher and emigrated from England in 1855.

Rutherford attended rural primary schools before his admission to Nelson College (a secondary school) in 1887. He excelled academically, and won a scholarship to Canterbury College at the University of New Zealand in 1889. He earned his bachelor’s degree in 1892. He continued on a mathematics scholarship and earned a master’s degree in 1893. His university work was primarily concentrated in research on magnetism and electrical technology.

In 1894 Rutherford won an 1851 Exhibition Science Scholarship and was accepted as a graduate research student at Trinity College at the University of Cambridge to work in the Cavendish Laboratory with physics professor J. J. Thomson, who would be credited with the discovery of the electron in 1897.

Life’s Work

Rutherford began working in the field of radiation and studied the conductivity of gases that were ionized by bombardment with X-rays. In 1896, he began conducting similar experiments using radiation from uranium. He noted two distinct types of rays: one consisting of positively-charged particles that did not penetrate matter, and another of negatively-charged particles (later shown to be high-speed electrons) that easily penetrated matter. He would later name these alpha and beta rays. These experiments marked the beginning of Rutherford’s lifelong study of radioactivity and atomic particles.

Rutherford received his research degree from Cambridge in 1897. The next year, he accepted the position of the Macdonald Chair of Physics at McGill University in Montreal, Canada. There, he studied the radioactive decay of thorium. About three times as common but significantly less radioactive than uranium, its decay produces an isotope of radon (then called thoron). Radon was the last of the noble (inert) gases to be isolated. During his time in Montreal, Rutherford married Mary Georgina Newton in 1900. They would have one daughter, Eileen.

In working with radon, Rutherford noted that radiation dissipated in geometrical progression with time. In 1905, he would extend this predictable “half-life” principal to use radium to date rocks, a process later extensively used with carbon-14 to date biological material. These experiments provided the first accurate formulation and proof of the process by which radioactive elements break down at the atomic level as heavy atoms release radiation and create new, slightly lighter atoms. For example, radium becomes lead-206, and carbon-14 decays to become nitrogen-14.

Rutherford documented his work in numerous published research papers, and was elected to England’s Royal Society in 1903. He published the book Radioactivity in 1904. His Silliman Lectures at Yale University were collected in the 1906 work Radioactive Transformations.

In 1907, Rutherford took a position as the Langworthy Professor of Physics at the University of Manchester in England. In 1908 he received the Nobel Prize in Chemistry for his “investigations into the disintegration of the elements, and the chemistry of radioactive substances.” Beginning in the year after winning the Nobel, Rutherford entered a period in which he made many of his most significant discoveries. Working with German physicist Hans Geiger, he conducted further experiments in bombarding elements with radiation. By that time, Rutherford had named alpha particles and recognized that they were ionized helium atoms, stripped of their electrons. He began measuring the scattering of alpha particles when shot through thin sheets of metal.

In 1906, J. J. Thomson had extended his discovery of the electron to propose a new theory of the structure of the atom. In what was termed the “plum pudding model,” he conjectured that the atom contained numerous electrons (“plums”) spread throughout a positively-charged “pudding.”

However, in Rutherford’s experiments, the scattering of alpha particles was not uniform as predicted by Thomson’s model. In 1909, using very thin gold leaf, Rutherford, Geiger, and research assistant Ernest Marsden noted that some particles actually bounced backwards. It was impossible that electrons would cause such deflection, due to their small electrical force.

By 1911, Rutherford deduced that the only likely explanation for a force great enough to cause this scattering was that the positive charge in the atom is contained in a very small area, rather than being spread out. He was able to mathematically deduce by the degree of scattering that this positive nucleus must be extremely compact. Although not yet complete, this was the beginning of the first accurate model of the atom.

In 1912, another of Thomson’s former students, Niels Bohr, helped Rutherford refine his model of the atom by applying quantum theory to describe how electrons generally remain in stable orbits around the nucleus. Although this refinement is credited to Bohr, this theory is often referred to as the Rutherford-Bohr model of the atom. With H. G. Moseley, Rutherford extended his use of radiation to determine the atomic number (equal to the number of protons) of various elements.

In 1919, Rutherford announced that in experiments begun two years earlier, he had artificially “split” the atom by bombarding normally stable nitrogen with alpha particles to create fast protons (hydrogen) and an isotope of oxygen. Shortly after this discovery, he accepted an offer to succeed Thomson as the Cavendish Professor of Physics at the University of Cambridge.

Over the next two decades, Rutherford either directly or indirectly set into motion many of the pivotal discoveries of nuclear physics. In 1920, he predicted the existence of the neutron, an uncharged particle just slightly heavier than the proton. Because of the difficulty in physically detecting an uncharged particle, it was not until 1932 that Rutherford’s student at Cambridge, James Chadwick, would prove its existence.

After successfully lobbying the British government for funding in 1929, Rutherford oversaw John Cockcroft and Ernest T. S. Walton’s development of one of the first high-energy particle accelerators, a linear accelerator used to bombard elements with artificially accelerated protons. The cyclotron, a circular accelerator, was developed about the same time in the United States by Ernest Lawrence.

Along with Chadwick and Charles Drummond Ellis, Rutherford published Radiation from Radioactive Substances in 1930. Later works by Rutherford include The Artificial Transmutation of the Elements (1933) and The Newer Alchemy (1937).

Impact

The first nuclear fusion reaction was created at Rutherford’s Cambridge lab, as announced in 1934 by Marcus Oliphant and Paul Harteck. They bombarded concentrated heavy water (deuterium) with deuterons to produce tritium and helium. This process would lead to the creation of the hydrogen bomb, first detonated in 1952.

Although Enrico Fermi had unknowingly created atomic fission as early as 1934, fission was first detected in 1938 by Otto Hahn, one of Rutherford’s former students at McGill University. Hahn’s work was the precursor to the Manhattan Project, the atomic weapons program in the United States during World War II. Commercial fission power plants were introduced by the mid-1950s.

Rutherford himself anticipated neither the rapid development of nuclear weaponry nor nuclear power, as he was accustomed to the low-level radiation typified by the natural decay of heavy elements. It was not until physicist Leó Szilárd and others perfected means of instigating fission chain reactions that the vast energy of heavy elements could be released almost in an instant, instead of over millions of years.

J. Robert Oppenheimer, scientific director of the Manhattan Project, was one of Rutherford’s students at Cambridge. Students and research associates of Rutherford to win the Nobel Prize include James Chadwick, John Cockcroft, Ernest T. S.Walton, Patrick M. S. Blackett, G. P. Thomson (J. J. Thomson’s son), Edward V. Appleton, Francis W. Aston, and Cecil Powell.

In 1931, Rutherford was granted peerage as First Baron Rutherford of Nelson, New Zealand, and Cambridge, and became a member of the House of Lords, making his popular title Lord Rutherford. He died on October 19, 1937, at the age of sixty-six, due to complications from a hernia. His ashes are interred in Westminster Abbey in London.

Bibliography

Heilbron, John L. Ernest Rutherford and the Explosion of Atoms. New York: Oxford UP, 2003. Print. A biography of Rutherford that discusses his research and contributions to the field of physics, including his work with radioactivity and his discovery of atomic structure.

Reeves, Richard. A Force of Nature: The Frontier Genius of Ernest Rutherford. New York: Norton, 2008. Print. Discusses Rutherford’s life and the influence of his scientific work on history and politics. Contains information on his discovery of atomic structure.

Roberts, John. “Ernest Rutherford: Father of Nuclear Physics.” Nuclear Future 7.4 (2011): 28–31. Print. Presents information on the atomic nucleus and nuclear physics related to nuclear decay, nuclear magnetic resonance, radiocarbon dating, and fission.

Walker, Phil. “The Atomic Nucleus.” New Scientist 1 Oct. 2011: i–viii. Print. Describes Rutherford’s influence on the field of science as related to atomic theory and nuclear physics.