Ernest Rutherford, 1st Baron Rutherford of Nelson, OM FRS (30 August 1871 – 19 October 1937) was a New Zealand-born British physicist who became known as the father of nuclear physics. Encyclopædia Britannica considers him to be the greatest experimentalist since Michael Faraday (1791–1867).
In early work he discovered the concept of radioactive half-life, proved that radioactivity involved the transmutation of one chemical element to another, and also differentiated and named alpha and beta radiation. This work was done at McGill University in Canada. It is the basis for the Nobel Prize in Chemistry he was awarded in 1908 "for his investigations into the disintegration of the elements, and the chemistry of radioactive substances".
Rutherford moved in 1907 to the Victoria University of Manchester (today University of Manchester) in the UK, where he and Thomas Royds proved that alpha radiation is helium ions.[5][6] Rutherford performed his most famous work after he became a Nobel laureate. In 1911, although he could not prove that it was positive or negative, he theorized that atoms have their charge concentrated in a very small nucleus, and thereby pioneered the Rutherford model of the atom, through his discovery and interpretation of Rutherford scattering in his gold foil experiment. He is widely credited with first "splitting the atom" in 1917 in a nuclear reaction between nitrogen and alpha particles, in which he also discovered (and named) the proton.[9]
Rutherford became Director of the Cavendish Laboratory at Cambridge University in 1919. Under his leadership the neutron was discovered by James Chadwick
in 1932 and in the same year the first experiment to split the nucleus
in a fully controlled manner, performed by students working under his
direction, John Cockcroft and Ernest Walton. After his death in 1937, he was honoured by being interred with the greatest scientists of the United Kingdom, near Sir Isaac Newton's tomb in Westminster Abbey. The chemical element rutherfordium (element 104) was named after him in 1997.
Ernest Rutherford was the son of James Rutherford, a farmer, and his wife Martha Thompson, originally from Hornchurch, Essex, England.[10] James had emigrated to New Zealand from Perth, Scotland, "to raise a little flax and a lot of children". Ernest was born at Brightwater, near Nelson, New Zealand. His first name was mistakenly spelled 'Earnest' when his birth was registered.[11]
He studied at Havelock School and then Nelson College and won a scholarship to study at Canterbury College, University of New Zealand where he participated in the debating society and played rugby.[12] After gaining his BA, MA
and BSc, and doing two years of research during which he invented a new
form of radio receiver, in 1895 Rutherford was awarded an 1851 Research Fellowship from the Royal Commission for the Exhibition of 1851,[13] to travel to England for postgraduate study at the Cavendish Laboratory, University of Cambridge.[14]
He was among the first of the 'aliens' (those without a Cambridge
degree) allowed to do research at the university, under the inspiring
leadership of J. J. Thomson,
and the newcomers aroused jealousies from the more conservative members
of the Cavendish fraternity. With Thomson's encouragement, he managed
to detect radio waves at half a mile and briefly held the world record
for the distance over which electromagnetic waves could be detected,
though when he presented his results at the British Association meeting in 1896, he discovered he had been outdone by another lecturer, by the name of Marconi.
In 1898 Thomson offered Rutherford the chance of a post at McGill University in Montreal, Canada. He was to replace Hugh Longbourne Callendar who held the chair of Macdonald Professor of physics and was coming to Cambridge.[15]
Rutherford was accepted, which meant that in 1900 he could marry Mary
Georgina Newton (1876–1945) to whom he had become engaged before leaving
New Zealand; they had one daughter, Eileen Mary (1901–1930), who
married Ralph Fowler. In 1900 he gained a DSc from the University of New Zealand. In 1907 Rutherford returned to Britain to take the chair of physics at the University of Manchester.
At Cambridge, Rutherford started to work with J. J. Thomson on the
conductive effects of X-rays on gases, work which led to the discovery
of the electron which Thomson presented to the world in 1897. Hearing of 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, he coined the terms alpha ray and beta ray in 1899 to describe the two distinct types of radiation. He then discovered that thorium
gave off a gas which produced an emanation which was itself radioactive
and would coat other substances. He found that a sample of this
radioactive material of any size invariably took the same amount of time
for half the sample to decay – its "half-life" (11½ minutes in this case).
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 thorium
emanations. Once he had eliminated all the normal chemical reactions,
Soddy suggested that it must be one of the inert gases, which they named
thoron (later found to be an isotope of radon).
They also found another type of thorium they called Thorium X, and kept
on finding traces of helium. They also worked with samples of "Uranium
X" from William Crookes and radium from Marie Curie.
In 1902, they produced a "Theory of Atomic Disintegration" to account
for all their experiments. Up till then atoms were assumed to be the
indestructable 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 types of atoms (one element spontaneously being changed to another).
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 Manchester, he continued to work with alpha radiation. In conjunction with Hans Geiger, he developed zinc sulfide scintillation screens
and ionisation chambers to count alphas. By dividing the total charge
they produced by the number counted, Rutherford decided that the charge
on the alpha 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.
Rutherford performed his most famous work 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 deflecting 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, of a type not expected from any theory of matter
at that time. Such deflections, though rare, were found, and proved to
be a smooth but high-order function of the deflection angle. 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 [7] nucleus, containing much of the atom's mass, was orbited by low-mass electrons.
Before leaving Manchester in 1919 to take over the Cavendish
laboratory in Cambridge, Rutherford became, in 1919, the first person to
deliberately transmute one element into another.[4]
In this experiment, he had discovered peculiar radiations when alphas
were projected into air, and narrowed the effect down to the nitrogen,
not the oxygen in the air. Using pure nitrogen, Rutherford used alpha
radiation to convert nitrogen into oxygen through the nuclear reaction 14N + α → 17O
+ proton. The proton was not then known. In the products of this
reaction Rutherford simply identified hydrogen nuclei, by their
similarity to the particle radiation from earlier experiments in which
he had bombarded hydrogen gas with alpha particles to knock hydrogen
nuclei out of hydrogen atoms. 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 which were whole numbers
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 from the nucleus
that was lighter. Thus, Rutherford postulated hydrogen nuclei to be a
new particle in 1920, which he dubbed the proton.
In 1921, while working with Niels Bohr (who postulated that electrons moved in specific orbits), 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 from 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's theory of neutrons was proved in 1932 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.
Rutherford's 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. Rutherford's
team, using natural alpha particles, demonstrated induced nuclear transmutation, and later, using protons from an accelerator, demonstrated artificially-induced nuclear reactions and transmutation. He is known as the father of nuclear physics. 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 London paper The Times, was reported by Szilárd to have been his inspiration for thinking of the possibility of a controlled energy-producing nuclear chain reaction. Szilard had this idea while walking in London, on the same day.
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.
