1908 Age 36 yrs.
The Royal Swedish Academy of Sciences awarded him the Nobel Prize for Physics.
Rutherford along with Thomas Royds identified alpha particles as Helium atoms devoid of electrons. Alpha particle had an atomic mass of 4 and a positive charge of 2.
1909 Age 37 yrs.
Geiger announced that a 20 year old undergraduate, Ernest Marsden was looking for a research project. Important investigations Rutherford assigned to final year students. Here he made an exception. He wished Marsden to measure the deviations of alpha rays scattering through metal foils of various nature.
The assignment included, finding the relationships between the number of particles deflecting at a certain angle and the following:-
- The diameter of the scattering foil.
- Atomic mass of the metal used for scattering.
- The nuclear charge of the alpha source.
- Velocity of alpha particles.
They found gold to be ideal for this as it could be beaten into very thin sheets. The trio devised a zinc sulphide as fluorescent material, a rotating microscope to observe the individual flashes and a counting tube which developed into the Geiger Muller tube later on. They used Radium as the nuclear material instead of Radon gas.
Physicist were unable to explain how the atoms remain electrically neutral with the negatively charged electrons. One explanation given by JJ., was that the two kinds of particles, positives and negatives are scattered just as plums in a pudding. Nobody knew about a positive particles except alpha.
Marsden after getting adjusted to darkness stared at the screen to observe any particles getting reflected. He was such an obedient student, knowing nothing would come, stared at the fluorescent screen from the incident side. To his utter amazement he saw a tiny flash about once in every second. Geiger and Marsden checked the results over and over again only to find that the unbelievable was right. One in a few thousand particles deviated over 90 degrees.
They hesitantly reported to Rutherford “A few alpha particles not only deviated by large angles but about one in a thousand bounced back”.
He couldn’t believe his ears.. Later he has said that, “It was the most incredible event of his life, ‘as if you fired a 15-inch shell at a piece of tissue paper and it came back and hit you"
Rutherford knew that these observations of Geiger and Marsden would be an important landmark in the history of understanding matter. He permitted them to publish the paper on their own names enabling them to get the entire credit. Philosophy Magazine published it.
1910
Rutherford experimenting with Thomas Royds had discovered the nature of the alpha particle. It was 4 times as heavy as the Hydrogen atom and required 2 electrons to neutralize it.
Simple calculations based on statistics of Geiger and marsden showed that the atom was mostly empty space. The core or the central part, (at the time the word ‘nucleus’ had not been adopted.) amounted to only 1/100,000 the size of the atom.
‘Plum pudding model’ could not withstand the latest findings. He went back to history. In 1903 Hantaro Nagaoka had proposed a model with a heavy positive centre and orbiting electron in rings as in the planet Saturn. It was abandoned by the creator in 1908.
1911
Rutherford could not say whether the atom was a disc or a sphere. He did not know whether the core was positive or negative. ( Protons had not been discovered at the time) He could only say mass or the matter was mainly at the centre and the electrons are orbiting as the planets revolve round the sun. This was the ‘Solar model.’
1912
There was strong opposition for this model. They had to explain why the similar charges, clustered at the core do not repel each other and why the orbiting electrons do not lose energy and fall back to the centre. Although he predicted a strong force (now named Nuclear force) holding the similar charges together at the core of the atom electron problem remained unsolved.
The person who came to the rescue was the Danish scientist Niels Bohr. He showed mathematically that electrons can orbit at certain levels in a stable manner.
1916
He had foreseen the nuclear threat to mankind and stated , “I personally hope method of extracting atomic energy will not be discovered until man discovers friendly co-existence”
1930
Rutherford’s daughter Eileen passed away.
1932 The proton–neutron model of the nucleus was proposed by the Russian scientist Dmitry Ivanenko
Fig.4 Rutherford Bohr model of the atom
1937
Ernest Rutherford passed away due to a negligence of his illness. The ashes were buried in Westminster Abbey, in London
1991
‘The Rutherford Origin’, with information displays about Rutherford in a garden setting, was opened on December 6, his birthplace.
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