ERNEST RUTHERFORD
> He was a British-New Zealand chemist and physicist who became known as the father of nuclear physics. 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. He was awarded the Nobel Prize in Chemistry in 1908 "for his investigations into the disintegration of the elements, and the chemistry of radioactive substances". In 1911, he postulated that atoms have their positive charge concentrated in a very small nucleus. and thereby pioneered the Rutherford model, or planetary, 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, and leading the first experiment to "split the nucleus" in a controlled manner by two students under his direction, John Cockcroft and Ernest Walton in 1932. During the investigation of radioactivity he coined the terms alpha and beta in 1899 to describe the two distinct types of radiation emitted by thorium and uranium. These rays were differentiated on the basis of penetrating power. From 1900 to 1903 he was joined at McGill by the young Frederick Soddy (Nobel Prize in Chemistry, 1921) and they collaborated on research into the transmutation of elements. Rutherford had demonstrated that radioactivity was the spontaneous disintegration of atoms.Going through...
> Rutherford tested Thomson's hypothesis by devising his "gold foil" experiment. Ernest Rutherford and his two workers, Hans Gieger and Ernest Marsden had bombarded very thin metal foils with alpha particles from a radioactive source. In an experiment with gold foil, most of the particles went right through the foil with no scattering. However a few particles were deflected sharply. The conclusion of this experiment was that all positive charge and nearly all the mass of an atom are concentrated at the center of the atom in a tiny core called, “nucleus.” Rutherford discovered that the atom is mostly space with a dense positively charged nucleus surrounded by negative electrons. In Manchester he continued to work with alpha radiation, in conjunction with Hans Geiger he developed zinc sulfide scintillation screens and ionization 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 Rutherford 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 were trapped. Eventually, the clear spectrum of helium gas appeared, proving that alphas were at least ionized helium atoms, and probably helium nuclei. Along with Hans Geiger and Ernest Marsden he carried out the Geiger–Marsden experiment in 1909, which demonstrated the nuclear nature of atoms. It was his interpretation of this experiment that led him to formulate the Rutherford model of the atom in 1911 — that a very small positively charged nucleus was orbited by electrons. In Cambridge in 1919 he became the first person to transmute one element into another when he converted nitrogen into oxygen through the nuclear reaction 14N + α → 17O + p. In 1921, while working with Niels Bohr (who postulated that electrons moved in specific orbits), Rutherford theorized about the existence of neutrons, which could somehow compensate for the repelling effect of the positive charges of protons by causing an attractive nuclear force and thus keeping the nuclei from breaking apart. Rutherford's theory of neutrons was proved in 1932 by his associate James Chadwick, who in 1935 was awarded the Nobel Prize in Physics for this discovery. Rutherford reasoned that if Thomson's model was correct then the mass of the atom was spread out throughout the atom. Then, if he shot high velocity alpha particles (helium nuclei) at an atom then there would be very little to deflect the alpha particles.
RUTHERFORD MODEL
>He decided to test this with a thin film of gold atoms. As expected, most alpha particles went right through the gold foil but to his amazement a few alpha particles rebounded almost directly backwards. These deflections were not consistent with Thomson's model. Rutherford was forced to discard the Plum Pudding model and reasoned that the only way the alpha particles could be deflected backwards was if most of the mass in an atom was concentrated in a nucleus. He thus developed the planetary model of the atom which put all the protons in the nucleus and the electrons orbited around the nucleus like planets around the sun. Rutherford's new model for the atom, based on the experimental results, had the new features of a relatively high central charge concentrated into a very small volume in comparison to the rest of the atom and containing the bulk of the atomic mass.
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