100 years of the nuclear atom - Ernest Rutherford’s revolutionary discovery

4 May 2011, Comments: | Views: 4479 | | Category: Legends, Science

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The Rutherford–Bohr model of the hydrogen atom (Z = 1) or a hydrogen-like ion (Z > 1), where the negatively charged electron confined to an atomic shell encircles a small, positively charged atomic nucleus

This month is the centenary of what is arguably the most amazing discovery of the 20th century – that the apparently solid world around us is mainly empty space.

What are this Atoms and whats inside?

 Here's a quick flavour of just how strange an atom is. And remember atoms aren't obscure objects: everything in the world around us is made of atoms; we are made of atoms.

First of all, atoms are ridiculously small - they're about one tenth of a millionth of a millimetre across. That means that a human hair, one of the narrowest things visible to the eye is around a million atoms across. 

Put another way, there are more atoms in a glass of water than glasses of water in all the oceans in the world.  

And the story gets really strange. An atom isn't just tiny, it's over 99.999..% empty space. All the weight of an atom is concentrated in a mind-numbingly tiny object at its centre. It's a trillionth of a centimetre across and is called the nucleus.

To give you a sense of how empty an atom is - if the nucleus was the size of a football, the nearest electron would be half a mile (0.8km) away.If you removed all the empty space from the atoms that make up all the humans on the planet, then you could fit all 6 billion of us inside a single apple.

Yes, atoms the basic structural units of the entire universe are more than 99.9999% empty. (But empty space have quiet different meanings - quantum mechanics never speak of empty space - the electron is not a concentrated particle and it is the probability of finding the electron rather than position- and it's postiion can be any where in the atom with different probabilities and hence called electron cloud). Imagine how it will be when there is no empty space in an atom - the unverse would shrink to 0.00000001 % (you can put 12 zeros between '.' and '1' ).

Who Discovered The Emptiness of the Universe / Atom ?

This astonishing discovery that atoms are mainly empty was made in 1909 at Manchester University by the indefatigable Ernest Rutherford. Rutherford had great courage as a scientist and was prepared to fly in the face of convention.

So when he announced that the atom was mainly empty, he did so knowing his claim flatly contradicted the then known laws of physics. These demanded that all atoms collapse instantly. It was a seismic moment in the history of science.

Forced to explain the atom's mysterious emptiness, scientists had to jettison everything they had believed to be true for the previous two centuries. Their response was to invent an entirely new science, which we now call quantum mechanics..

In May 1911 Philosophical Magazine published a research paper by Ernest Rutherford. He had analysed the results of some measurements by Hans Geiger and Ernest Marsden, who worked with him at Manchester University. The analysis led Rutherford to the conclusion that all the positive electric charge within an atom, and most of the mass, must reside in a tiny central region, with the negatively charged electrons swirling round far away. The central core became known as the atomic nucleus and the study of it led to our understanding of the fundamental particles and forces in the Universe.

Rutherford - A Brief Biography

The Man Who Splitted the Invincible Atom

Ernest Rutherford is one of the most illustrious scientists of all time. 
He is to the atom what Darwin is to evolution, Newton to mechanics, Faraday to electricity and Einstein to relativity. His pathway from rural child to immortality is a fascinating one.

Rutherford's works ensure his immortality. As the The New York Times stated, in a eulogy accompanying the announcement of his unexpected and unnecessary death in 1937. " It is given to but few men to achieve immortality, still less to achieve Olympian rank, during their own lifetime. Lord Rutherford achieved both. In a generation that witnessed one of the greatest revolutions in the entire history of science he was universally acknowledged as the leading explorer of the vast infinitely complex universe within the atom, a universe that he was first to penetrate."

Not for him the fame based on one discovery. He radically altered our understanding of nature on three separate occasions. Through brilliantly conceived experiments, and with special insight, he explained the perplexing problem of radioactivity as the spontaneous disintegration of atoms (they were not necessarily stable entities as had been assumed since the time of the ancient Greeks), he determined the structure of the atom and he was the world's first successful alchemist (he converted nitrogen into oxygen). Or put another way, he was first to split the atom.

  Any of his secondary discoveries, such as dating the age of the Earth, would have given fame to a lesser scientist. For example, the first method invented to detect individual nuclear particles by electrical means, the Rutherford-Geiger detector, evolved into the Geiger-Muller tube. The modern smoke detector, responsible for saving so many lives in house fires, can be traced back to 1899 when, at McGill University in Canada, Rutherford blew tobacco smoke into his ionisation chamber and observed the change in ionisation.

Early Life and Schooling

Ernest Rutherford was born on August 30, 1871, in Nelson, New Zealand, the fourth child and second son in a family of seven sons and five daughters. His father James Rutherford, a Scottish wheelwright, emigrated to New Zealand with Ernest's grandfather and the whole family in 1842. His mother, née Martha Thompson, was an English schoolteacher, who, with her widowed mother, also went to live there in 1855.

Ernest received his early education in Government schools and at the age of 16 entered Nelson Collegiate School. In 1889 he was awarded a University scholarship and he proceeded to the University of New Zealand, Wellington, where he entered Canterbury College*. He graduated M.A. in 1893 with a double first in Mathematics and Physical Science and he continued with research work at the College for a short time, receiving the B.Sc. degree the following year. That same year, 1894, he was awarded an 1851 Exhibition Science Scholarship, enabling him to go to Trinity College, Cambridge, as a research student at the Cavendish Laboratory under J.J. Thomson. In 1897 he was awarded the B.A. Research Degree and the Coutts-Trotter Studentship of Trinity College. An opportunity came when the Macdonald Chair of Physics at McGill University, Montreal, became vacant, and in 1898 he left for Canada to take up the post.

Galore of Discoveries

The Alpha Scattering Experiment which led to the discovery 

Rutherford returned to England in 1907 to become Langworthy Professor of Physics in the University of Manchester, succeeding Sir Arthur Schuster, and in 1919 he accepted an invitation to succeed Sir Joseph Thomson as Cavendish Professor of Physics at Cambridge. He also became Chairman of the Advisory Council, H.M. Government, Department of Scientific and Industrial Research; Professor of Natural Philosophy, Royal Institution, London; and Director of the Royal Society Mond Laboratory, Cambridge.

On his arrival at Cambridge his talents were quickly recognized by Professor Thomson. During his first spell at the Cavendish Laboratory, he invented a detector for electromagnetic waves, an essential feature being an ingenious magnetizing coil containing tiny bundles of magnetized iron wire. He worked jointly with Thomson on the behaviour of the ions observed in gases which had been treated with X-rays, and also, in 1897, on the mobility of ions in relation to the strength of the electric field, and on related topics such as the photoelectric effect. In 1898 he reported the existence of alpha and beta rays in uranium radiation and indicated some of their properties. Otto Hahn, who discovered atomic fission, worked under Rutherford at the Montreal Laboratory in 1905-06.

 At Manchester, Rutherford continued his research on the properties of the radium emanation and of the alpha rays and, in conjunction with H. Geiger, a method of detecting a single alpha particle and counting the number emitted from radium was devised. In 1910, his investigations into the scattering of alpha rays and the nature of the inner structure of the atom which caused such scattering led to the postulation of his concept of the "nucleus", his greatest contribution to physics. According to him practically the whole mass of the atom and at the same time all positive charge of the atom is concentrated in a minute space at the centre.

An inspiring leader of the Cavendish Laboratory, he steered numerous future Nobel Prize winners towards their great achievements: Chadwick, Blackett, Cockcroft and Walton; while other laureates worked with him at the Cavendish for shorter or longer periods: G.P. Thomson, Appleton, Powell, and Aston. C.D. Ellis, his co-author in 1919 and 1930, pointed out "that the majority of the experiments at the Cavendish were really started by Rutherford's direct or indirect suggestion". He remained active and working to the very end of his life.

Rutherford published several books: Radioactivity (1904); Radioactive Transformations (1906), being his Silliman Lectures at Yale University; Radiation from Radioactive Substances, with James Chadwick and C.D. Ellis (1919, 1930) - a thoroughly documented book which serves as a chronological list of his many papers to learned societies, etc.; The Electrical Structure of Matter (1926); The Artificial Transmutation of the Elements (1933); The Newer Alchemy (1937).


Left, lower centre and right: stamps with the nuclear atom, the symbol most associated with Rutherford. Upper centre: a Soviet stamp showing the diagram from Rutherford’s paper of May 1911, illustrating what is now known as Rutherford scattering

Rutherford was knighted in 1914; he was appointed to the Order of Merit in 1925, and in 1931 he was created First Baron Rutherford of Nelson, New Zealand, and Cambridge. He was elected Fellow of the Royal Society in 1903 and was its President from 1925 to 1930. Amongst his many honours, he was awarded the Rumford Medal (1905) and the Copley Medal (1922) of the Royal Society, the Bressa Prize (1910) of the Turin Academy of Science, the Albert Medal (1928) of the Royal Society of Arts, the Faraday Medal (1930) of the Institution of Electrical Engineers, the D.Sc. degree of the University of New Zealand, and honorary doctorates from the Universities of Pennsylvania, Wisconsin, McGill, Birmingham, Edinburgh, Melbourne, Yale, Glasgow, Giessen, Copenhagen, Cambridge, Dublin, Durham, Oxford, Liverpool, Toronto, Bristol, Cape Town, London and Leeds.

Rutherford’s Nobel Prize in Chemistry of 1908 was too recent for physicists to nominate him again for a prize. It was to be 1922 before he was next nominated, unsuccessfully. There have been 27 Nobel prizes awarded for the discovery of, or theories linking, subatomic particles but there was never one for the nuclear atom.

Rutherford married Mary Newton, only daughter of Arthur and Mary de Renzy Newton, in 1900. Their only child, Eileen, married the physicist R.H. Fowler. Rutherford's chief recreations were golf and motoring.

He died in Cambridge on October 19, 1937. His ashes were buried in the nave of Westminster Abbey, just west of Sir Isaac Newton's tomb and by that of Lord Kelvin.

For more on  Rutherford  - > http://www.rutherford.org.nz/

(Src : From Nobel Lectures, Chemistry 1901-1921, Elsevier Publishing Company, Amsterdam, 1966)

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