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of the atom is concentrated in
this minute centre along with
all the positive charges. To
come to this conclusion, he had conducted his famous gold-
foil experiment along with the coworkers, Hans Geiger and
Ernest Marsden, in which he
had bombarded a thin gold foil
with α-rays and found that most
of the rays passed through it,
while only a few retraced their
paths. So, he visualized most
part of the atom to be almost
empty through which the α-rays
passed and the deflection of
the few was caused by dense
centre (1911). It gave a death
blow to the Thomson’s plum- pudding structure of atom. In
1919, Rutherford discovered
proton, the positively charged
particle which according to him constituted the centre of the
atom and deflected the α-rays.
Later he also put out the idea
that there could be another
type of particle with mass but
no charge. He called it neutron
and imagined it as a pair of negatively charged electron and positively charged proton.
From all these he visualized the planetary model of atom in which the massive protons and neutrons constituted the centre or nucleus, while the electrons with negligible masses moved around it in various orbits as do the planets around the sun. In 1932, James Chadwick discovered neutron. Rutherford also suggested that the numbers of protons in the nucleus are equal to the numbers of electrons moving around it, which matches with the atomic number of the atom. In order to account for the stability of the atom he proposed that the electrons revolve in closed orbits. Thus their centrifugal force balances the force of attraction and keeps them in their paths.
However, according to the classical electromagnetic theory, a moving charge must use some energy. So the electrons should do it. As a consequence, those should lose energy and come closer
Rutherford at Manchester in 1910
during the process fast protons would be emitted. Later, Patrick Blackett proved with the cloud chamber that nitrogen in this process could be transformed in to an oxygen isotope.
Rutherford was an inspiring leader of the Cavendish laboratory that produced many Nobel Laureates like Chadwick, Blackett, Cockcroft, Walton, G.P. Thomson, Appleton,
Powell and Aston. Most of their prize-winning research had begun by Rutherford’s direct or indirect suggestions. He also published several books such as Radioactivity (1904); Radioactive Transformation (1906); The Electrical Structure of Matter (1926); The Artificial Transmutation of Elements (1938); The Newer Alchemy (1937); and Radiation from Radioactive substances (1930, co-authored with James
Chadwick and C.D. Ellis). Rutherford was Knighted in 1914, appointed to the Order of Merit (1925), elected Fellow of the Royal Society (1903) and was its President (1925-1930). He won the Faraday Medal from the Institution of Electrical Engineers (1930) and received the D.Sc. degree from the University of New Zealand as well as honorary doctorates from many other renowned Universities including the Wisconsin, the Pennsylvania, the Oxford, the Cambridge and the Leeds. In 1931 he was made the first Baron Rutherford of
Nelson, New Zealand and Cambridge. Rutherford was married to Mary Newton in 1900 and had a daughter from her. He died in Cambridge on 9 October 1937. His ashes were buried at Westminster Abbey, near the tombs of
Sir Isaac Newton and Lord Kelvin.
Dr Ramesh Chandra Parida is retired professor, Odisha University of Agriculture & Technology and Himansu Sekhar Fatesingh is a Freelance science writer and teacher. Emails: paridanana47@gmail.com; himansu1972@gmail.com
Rutherford with Hans Geiger
and closer to the nucleus and fall into it, destroying the atom. But it does not happen. It was considered as a major drawback of Rutherford’s atomic model.
In 1912, Niels Bohr joined him. He accepted his concept of nuclear structure of atom, adopted it to Max Plank’s quantum theory and postulated that moving electrons do not lose energy as long as they move in certain definite paths each having a specific energy. Those are called as energy levels or orbits. With later improvements, taking into account the Heisenberg’s concepts, it remains valid even today.
In 1913, Rutherford, in association with H.G. Moseley, bombarded cathode rays to atoms of various elements. They showed that the inner structures of those correspond with a group of lines which characterise the element. During his last year at Manchester (1919) he discovered that the nuclei of certain light elements like nitrogen could be “disintegrated” by the impact of energetic α-particles coming from the radioactive source, and
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