Ernest Rutherford


The Lord Rutherford of Nelson

Rutherford c. 1920s
Born
Ernest Rutherford

(1871-08-30)30 August 1871
Died19 October 1937(1937-10-19) (aged 66)
Cambridge, England
Resting placeWestminster Abbey
Alma mater
Known for
Spouse
Mary Georgina Newton
(m. 1900)
Children1
Awards
Scientific career
Fields
Institutions
Academic advisors
Doctoral students
Other notable students
President of the Royal Society
In office
1925–1930
Preceded byCharles Scott Sherrington
Succeeded byFrederick Gowland Hopkins
Signature

Ernest Rutherford, 1st Baron Rutherford of Nelson, OM, PRS, HonFRSE (30 August 1871 – 19 October 1937) was a New Zealand physicist who was a pioneering researcher in both atomic and nuclear physics. Rutherford has been described as "the father of nuclear physics", and "the greatest experimentalist since Michael Faraday". In 1908, he was awarded the Nobel Prize in Chemistry "for his investigations into the disintegration of the elements, and the chemistry of radioactive substances." He was the first Oceanian Nobel laureate, and the first to perform the awarded work in Canada.

Rutherford's discoveries include the concept of radioactive half-life, the radioactive element radon, and the differentiation and naming of alpha and beta radiation. Together with Thomas Royds, Rutherford is credited with proving that alpha radiation is composed of helium nuclei. In 1911, he theorized that atoms have their charge concentrated in a very small nucleus. This was done through his discovery and interpretation of Rutherford scattering during the gold foil experiment performed by Hans Geiger and Ernest Marsden, resulting in his conception of the Rutherford model of the atom. In 1917, he performed the first artificially-induced nuclear reaction by conducting experiments where nitrogen nuclei were bombarded with alpha particles. As a result, he discovered the emission of a subatomic particle which he initially called the "hydrogen atom", but later (more accurately) named the proton. He is also credited with developing the atomic numbering system alongside Henry Moseley. His other achievements include advancing the fields of radio communications and ultrasound technology.

Rutherford became Director of the Cavendish Laboratory at the University of Cambridge in 1919. Under his leadership, the neutron was discovered by James Chadwick in 1932. In the same year, the first controlled experiment to split the nucleus was performed by John Cockcroft and Ernest Walton, working under his direction. In honour of his scientific advancements, Rutherford was recognized as a Baron in the peerages of New Zealand and Britain. After his death in 1937, he was buried in Westminster Abbey near Charles Darwin and Isaac Newton. The chemical element rutherfordium (104Rf) was named after him in 1997.

Early life and education

Ernest Rutherford was born on 30 August 1871 in Brightwater, a town near Nelson, New Zealand. He was the fourth of twelve children of James Rutherford, an immigrant farmer and mechanic from Perth, Scotland, and his wife Martha Thompson, a schoolteacher from Hornchurch, England. Rutherford's birth certificate was mistakenly written as 'Earnest'. He was known by his family as Ern.

When Rutherford was five he moved to Foxhill and attended Foxhill School. At age 11 in 1883, his father moved the Rutherford family moved to Havelock, a town in the Marlborough Sounds. The move was made to be closer to the a flax mill the father was operating near the Ruapaka Stream. Ernest studied at Havelock School.

In 1887, on his second attempt, he won a scholarship to study at Nelson College. On his first examination attempt, he received 75 out of 130 marks for geography, 76 out of 130 for history, 101 out of 140 for English, and 200 out of 200 for arithmetic, totalling 452 out of 600 marks. With these marks, he had the highest of anyone from Nelson. When he was awarded the scholarship, he had received 580 out of 600 possible marks. After being awarded the scholarship, Havelock School presented him with a five-volume set of books titled The Peoples of the World. He studied at Nelson College between 1887 and 1889, and was head boy in 1889. He also played in the school's rugby team. He was offered a cadetship in government service, but he declined as he still had 15 months of college remaining.

In 1889, after his second attempt, he won a scholarship to study at Canterbury College, University of New Zealand, between 1890 and 1894. He participated in its debating society and the Science Society. At Canterbury, he was awarded a complex BA in Latin, English, and Maths in 1892, a MA in Mathematics and Physical Science in 1893, and a BSc in Chemistry and Geology in 1894.

Thereafter, he invented a new form of radio receiver, and in 1895 Rutherford was awarded an 1851 Research Fellowship from the Royal Commission for the Exhibition of 1851, to travel to England for postgraduate study at the Cavendish Laboratory, University of Cambridge. In 1897, he was awarded a BA Research Degree and the Coutts-Trotter Studentship from Trinity College, Cambridge.

Scientific career

Rutherford in 1892, aged 21

When Rutherford began his studies at Cambridge, he was among the first 'aliens' (those without a Cambridge degree) allowed to do research at the university, and was additionally honoured to study under J. J. Thomson.

With Thomson's encouragement, Rutherford detected radio waves at 0.5 miles (800 m), and briefly held the world record for the distance over which electromagnetic waves could be detected, although when he presented his results at the British Association meeting in 1896, he discovered he had been outdone by Guglielmo Marconi, whose radio waves had sent a message across nearly 10 miles (16 km).

Work with radioactivity

Again under Thomson's leadership, Rutherford worked on the conductive effects of X-rays on gases, which led to the discovery of the electron, the results first presented by Thomson in 1897. Hearing of Henri Becquerel's experience with uranium, Rutherford started to explore its radioactivity, discovering two types that differed from X-rays in their penetrating power. Continuing his research in Canada, in 1899 he coined the terms "alpha ray" and "beta ray" to describe these two distinct types of radiation.

In 1898, Rutherford was accepted to the chair of Macdonald Professor of physics position at McGill University in Montreal, Canada, on Thomson's recommendation. From 1900 to 1903, he was joined at McGill by the young chemist Frederick Soddy (Nobel Prize in Chemistry, 1921) for whom he set the problem of identifying the noble gas emitted by the radioactive element thorium, a substance which was itself radioactive and would coat other substances. Once he had eliminated all the normal chemical reactions, Soddy suggested that it must be one of the inert gases, which they named thoron. This substance was later found to be 220Rn, an isotope of radon. They also found another substance they called Thorium X, later identified as 224Rn, and continued to find traces of helium. They also worked with samples of "Uranium X" (protactinium), from William Crookes, and radium, from Marie Curie. Rutherford further investigated thoron in conjunction with R.B. Owens and found that a sample of radioactive material of any size invariably took the same amount of time for half the sample to decay (in this case, 1112 minutes), a phenomenon for which he coined the term "half-life". Rutherford and Soddy published their paper "Law of Radioactive Change" to account for all their experiments. Until then, atoms were assumed to be the indestructible basis of all matter; and although Curie had suggested that radioactivity was an atomic phenomenon, the idea of the atoms of radioactive substances breaking up was a radically new idea. Rutherford and Soddy demonstrated that radioactivity involved the spontaneous disintegration of atoms into other, as yet, unidentified matter.

In 1903, Rutherford considered a type of radiation, discovered (but not named) by French chemist Paul Villard in 1900, as an emission from radium, and realised that this observation must represent something different from his own alpha and beta rays, due to its very much greater penetrating power. Rutherford therefore gave this third type of radiation the name of gamma ray. All three of Rutherford's terms are in standard use today – other types of radioactive decay have since been discovered, but Rutherford's three types are among the most common. In 1904, Rutherford suggested that radioactivity provides a source of energy sufficient to explain the existence of the Sun for the many millions of years required for the slow biological evolution on Earth proposed by biologists such as Charles Darwin. The physicist Lord Kelvin had argued earlier for a much younger Earth, based on the insufficiency of known energy sources, but Rutherford pointed out, at a lecture attended by Kelvin, that radioactivity could solve this problem. Later that year, he was elected as a member to the American Philosophical Society, and in 1907 he returned to Britain to take the chair of physics at the Victoria University of Manchester.

In Manchester, Rutherford continued his work with alpha radiation. In conjunction with Hans Geiger, he developed zinc sulfide scintillation screens and ionisation chambers to count alpha particles. By dividing the total charge they produced by the number counted, Rutherford decided that the charge on the alpha particle was two. In late 1907, Ernest Rutherford and Thomas Royds allowed alphas to penetrate a very thin window into an evacuated tube. As they sparked the tube into discharge, the spectrum obtained from it changed, as the alphas accumulated in the tube. Eventually, the clear spectrum of helium gas appeared, proving that alphas were at least ionised helium atoms, and probably helium nuclei. Ernest Rutherford was awarded the 1908 Nobel Prize in Chemistry "for his investigations into the disintegration of the elements, and the chemistry of radioactive substances".

Model of the atom

Top: Expected results: alpha particles passing through the plum pudding model of the atom undisturbed.
Bottom: Observed results: a small portion of the particles were deflected, indicating a small, concentrated charge. Diagram is not to scale; in reality the nucleus is vastly smaller than the electron shell.

Rutherford continued to make ground-breaking discoveries long after receiving the Nobel prize in 1908. Along with Hans Geiger and Ernest Marsden in 1909, he carried out the Geiger–Marsden experiment, which demonstrated the nuclear nature of atoms by measuring the deflection of alpha particles passing through a thin gold foil. Rutherford was inspired to ask Geiger and Marsden in this experiment to look for alpha particles with very high deflection angles, which was not expected according to any theory of matter at that time. Such deflection angles, although rare, were found. It was Rutherford's interpretation of this data that led him to formulate the Rutherford model of the atom in 1911 – that a very small charged nucleus, containing much of the atom's mass, was orbited by low-mass electrons.

In 1912, Rutherford was joined by Niels Bohr (who postulated that electrons moved in specific orbits). Bohr adapted Rutherford's nuclear structure to be consistent with Max Planck's quantum theory, and the resulting Rutherford–Bohr model is considered valid to this day.

Piezoelectricity

During World War I, Rutherford worked on a top-secret project to solve the practical problems of submarine detection. Both Rutherford and Paul Langevin suggested the use of piezoelectricity, and Rutherford successfully developed a device which measured its output. The use of piezoelectricity then became essential to the development of ultrasound as it is known today. The claim that Rutherford developed sonar, however, is a misconception, as subaquatic detection technologies utilize Langevin's transducer.

Discovery of the proton

Together with H.G. Moseley, Rutherford developed the atomic numbering system in 1913. Rutherford and Moseley's experiments used cathode rays to bombard various elements with streams of electrons and observed that each element responded in a consistent and distinct manner. Their research was the first to assert that each element could be defined by the properties of its inner structures – an observation that later led to the discovery of the atomic nucleus. This research led Rutherford to theorize that the hydrogen atom (at the time the least massive entity known to bear a positive charge) was a sort of "positive electron" – a component of every atomic element.

It was not until 1919 that Rutherford expanded upon his theory of the "positive electron" with a series of experiments beginning shortly before the end of his time at Manchester. He found that nitrogen, and other light elements, ejected a proton, which he called a "hydrogen atom", when hit with α (alpha) particles. In particular, he showed that particles ejected by alpha particles colliding with hydrogen have unit charge and 1/4 the momentum of alpha particles.

Rutherford returned to the Cavendish Laboratory in 1919, succeeding J. J. Thomson as the Cavendish professor and the laboratory's director, posts that he held until his death in 1937. During his tenure, Nobel prizes were awarded to James Chadwick for discovering the neutron (in 1932), John Cockcroft and Ernest Walton for an experiment that was to be known as splitting the atom using a particle accelerator, and Edward Appleton for demonstrating the existence of the ionosphere.

Development of proton and neutron theory

In 1919–1920, Rutherford continued his research on the "hydrogen atom" to confirm that alpha particles break down nitrogen nuclei and to affirm the nature of the products. This result showed Rutherford that hydrogen nuclei were a part of nitrogen nuclei (and by inference, probably other nuclei as well). Such a construction had been suspected for many years, on the basis of atomic weights that were integral multiples of that of hydrogen; see Prout's hypothesis. Hydrogen was known to be the lightest element, and its nuclei presumably the lightest nuclei. Now, because of all these considerations, Rutherford decided that a hydrogen nucleus was possibly a fundamental building block of all nuclei, and also possibly a new fundamental particle as well, since nothing was known to be lighter than that nucleus. Thus, confirming and extending the work of Wilhelm Wien, who in 1898 discovered the proton in streams of ionized gas, in 1920 Rutherford postulated the hydrogen nucleus to be a new particle, which he dubbed the proton.

In 1921, while working with Niels Bohr, Rutherford theorized about the existence of neutrons, (which he had christened in his 1920 Bakerian Lecture), which could somehow compensate for the repelling effect of the positive charges of protons by causing an attractive nuclear force and thus keep the nuclei from flying apart, due to the repulsion between protons. The only alternative to neutrons was the existence of "nuclear electrons", which would counteract some of the proton charges in the nucleus, since by then it was known that nuclei had about twice the mass that could be accounted for if they were simply assembled from hydrogen nuclei (protons). But how these nuclear electrons could be trapped in the nucleus, was a mystery. Rutherford is widely quoted as saying, regarding the results of these experiments: "It was quite the most incredible event that has ever happened to me in my life. It was almost as incredible as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you."

In 1932, Rutherford's theory of neutrons was proved by his associate James Chadwick, who recognized neutrons immediately when they were produced by other scientists and later himself, in bombarding beryllium with alpha particles. In 1935, Chadwick was awarded the Nobel Prize in Physics for this discovery.

Re-evaluation of nuclear transmutation credit

From as early as 1948 to at least 2017, there was a long-standing myth that Rutherford was the first scientist to observe and report an artificial transmutation of a stable element into another element: nitrogen into oxygen. It was thought by many people to be one of Rutherford's greatest accomplishments. The New Zealand government even issued a commemorative stamp in the belief that the nitrogen-to-oxygen discovery belonged to Rutherford. Beginning in 2017, many scientific institutions corrected their versions of this history to indicate that the credit for the discovery belongs to Patrick Blackett, who undertook this research at Rutherford's suggestion and with his help and advice. Rutherford did detect the ejected proton in 1919 and interpreted it as evidence for disintegration of the nitrogen nucleus (to lighter nuclei). In 1925, Blackett showed that the actual product is oxygen and identified the true reaction as 14N + α → 17O + p. Rutherford therefore recognized "that the nucleus may increase rather than diminish in mass as the result of collisions in which the proton is expelled".

Later years and honours

Rutherford received significant recognition in his home country of New Zealand. In 1901, he earned a DSc from the University of New Zealand. In 1916, he was awarded the Hector Memorial Medal. In 1925, Rutherford called for the New Zealand Government to support education and research, which led to the formation of the Department of Scientific and Industrial Research (DSIR) in the following year. In 1933, Rutherford was one of the two inaugural recipients of the T. K. Sidey Medal, which was established by the Royal Society of New Zealand as an award for outstanding scientific research.

Additionally, Rutherford received a number of awards from the British Crown. He was knighted in 1914. He was appointed to the Order of Merit in the 1925 New Year Honours. Between 1925 and 1930, he served as President of the Royal Society, and later as president of the Academic Assistance Council which helped almost 1,000 university refugees from Germany. In 1931 was raised to the peerage as Baron Rutherford of Nelson, decorating his coat of arms with a kiwi and a Māori warrior. The title became extinct upon his unexpected death in 1937.

Personal life and death

The young Rutherford made his grandmother a wooden potato masher, which was believed to have been made during the school holidays. It has been held in the collection of the Royal Society since 1888.

In 1900, Rutherford married Mary Georgina Newton (1876–1954), to whom he had become engaged before leaving New Zealand, at St Paul's Anglican Church, Papanui in Christchurch. They had one daughter, Eileen Mary (1901–1930), who married the physicist Ralph Fowler. Rutherford's hobbies included golf and motoring.

For some time before his death, Rutherford had a small hernia, which he neglected to have fixed, and it became strangulated, rendering him violently ill. Despite an emergency operation in London, he died four days afterwards, at Cambridge on 19 October 1937 at age 66, of what physicians termed "intestinal paralysis". After cremation at Golders Green Crematorium, he was given the high honour of burial in Westminster Abbey, near Isaac Newton and other illustrious British scientists such as Charles Darwin.

Legacy

A statue of a young Ernest Rutherford at his memorial in Brightwater, New Zealand.

Rutherford is considered to be among the greatest scientists in history. At the opening session of the 1938 Indian Science Congress, which Rutherford had been expected to preside over before his death, astrophysicist James Jeans spoke in his place and deemed him "one of the greatest scientists of all time", saying:

In his flair for the right line of approach to a problem, as well as in the simple directness of his methods of attack, [Rutherford] often reminds us of Faraday, but he had two great advantages which Faraday did not possess, first, exuberant bodily health and energy, and second, the opportunity and capacity to direct a band of enthusiastic co-workers. Great though Faraday's output of work was, it seems to me that to match Rutherford's work in quantity as well as in quality, we must go back to Newton. In some respects he was more fortunate than Newton. Rutherford was ever the happy warrior – happy in his work, happy in its outcome, and happy in its human contacts.

Nuclear physics

Rutherford is known as "the father of nuclear physics" because his research, and work done under him as laboratory director, established the nuclear structure of the atom and the essential nature of radioactive decay as a nuclear process. Patrick Blackett, a research fellow working under Rutherford, using natural alpha particles, demonstrated induced nuclear transmutation. Later, Rutherford's team, using protons from an accelerator, demonstrated artificially-induced nuclear reactions and transmutation.

Rutherford died too early to see Leó Szilárd's idea of controlled nuclear chain reactions come into being. However, a speech of Rutherford's about his artificially-induced transmutation in lithium, printed in the 12 September 1933 issue of The Times, was reported by Szilárd to have been his inspiration for thinking of the possibility of a controlled energy-producing nuclear chain reaction.

Rutherford's speech touched on the 1932 work of his students John Cockcroft and Ernest Walton in "splitting" lithium into alpha particles by bombardment with protons from a particle accelerator they had constructed. Rutherford realized that the energy released from the split lithium atoms was enormous, but he also realized that the energy needed for the accelerator, and its essential inefficiency in splitting atoms in this fashion, made the project an impossibility as a practical source of energy (accelerator-induced fission of light elements remains too inefficient to be used in this way, even today). Rutherford's speech in part, read:

We might in these processes obtain very much more energy than the proton supplied, but on the average we could not expect to obtain energy in this way. It was a very poor and inefficient way of producing energy, and anyone who looked for a source of power in the transformation of the atoms was talking moonshine. But the subject was scientifically interesting because it gave insight into the atoms.

The element rutherfordium, Rf, Z=104, was named in honour of Rutherford in 1997.

Publications

Articles

  • "Disintegration of the Radioactive Elements" Harper's Monthly Magazine, January 1904, pages 279 to 284.

See also

Footnotes

  1. ^ See the article on Kelvin for details of his arguments.

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