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Matter

Rutherford's discovery of the nucleus was the latest event in a long-running scientific debate about the nature of matter. The Greek philosopher Democritus was the first to propose that the world was made up of tiny, indivisible, indestructible particles, which he called atoms, from the Greek word atomos, or indivisible. He believed that atoms were differently shaped and organized depending on the material they made up, but his theory was dismissed by Socrates and later Greek scientists and philosophers, and was not taken seriously again until the 17th century.

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The first proof of the existence of atoms was put toward in 1803 by an English Quaker, John Dalton, who carried out experiments with gases in order to investigate the chemical elements. Substances that cannot be broken down into anything simpler. He declared that each element had a distinctive type of atom, different from the atoms of any other element, and that atoms of each element had a different masses.

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Dalton drew up a pioneering table listing chemical elements and compunds by symbols.

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Another English scientist, Joseph John Thomson, made a vital addition to the understanding of atoms in 1897. He showed that the atom as far from being a solid structure as Dalton had believed, actually contained smaller particles. Thomson, like many other scientist of the period, experimented by passing an electric current through a glass vacuum tube. The electricity produced so-called 'cathode rays' within the tube, and these in turn produced a bright spot at one end of it. Having demonstrated that the cathode rays were deflected both by electric and magnetic fields. Thomson concluded that they consisted of a stream of negatively charged particles, much lighter than atoms. He called the particles as electrons.

The Split

Rutherford made his second celebrated breakthrough of smashing the nucleus of an atom in Cambridge. The simple apparatus he used consisted of a short brass tube which contained a movable arm holding radioactive radium.

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Atom Smasher, An 8 inches sealed brass tube, into which Rutherford introduced gases and radioactive material, made possible a remarkable discovery that atoms could be split.

Rutherford stretched thin metal foil across a window at one end and positioned a screen covered in zinc sulphide next to the foil. The tube was filled with nitrogen through an inlet pipe, and using the zinc sulphide screen, he observed the action of the alpha particles on the gas.

The strip of foil across the window was thick enough to stop the nitrogen atoms and radiation escaping from the tube. But as Rutherford watched the zonc sulphide screen, he saw flashes suggesting that some particles were escaping. Using his judgement as to what kind of particles would be able to pass through the foil, he concluded that they were hydrogen nuclei travelling at high speed.

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Escaping Particles, Rutherfor's experiments led him to a startling conclusion that under the impact of alpha particles from radioactive radium, nitrogen atoms were breaking up and so releasing hydrogen nuclei, later called 'protons'.

He seemed to have achieved what alchemists had struggled to do for centuries, and transmuted matter. It was a huge advance in the long task of unlocking the secrets of the atom.