Nuclear Physics - 1

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1. Great Discovery, Humble Beginning…

The 19th and the 20th centuries were the time for the most breath-taking discoveries and inventions of modern science. What was once considered fiction and everything that was ever dreamt of - flying machines for carrying people non-stop from continent to continent, submarines which could travel under water from Pole to Pole even under ice, rockets to carry us to the other worlds in the universe, apparatus to make it possible to converse over long distances without wires, and what not.

The development of science and technology outran the fantasies of the writers and the dreams of the scientists. One of the miracles of the era was the discovery of a mysterious chemical, a matchbox full of which could produce enough energy to propel a large ship for several years! The secret to its vast energy lies deep inside the matter that surrounds us.

At the turn of the 20th century, little was known about the structure of matter. Not all elements had been discovered, however it had been established that all matter was made of atoms. Atoms were believed to the smallest, and hence indivisible, particles of matter. J J Thomson then discovered the electron, the smallest particle of negative charge and soon Robert Millikan determined the mass of an electron to be 1836 times lighter than an atom of hydrogen, the lightest of all elements. In 1898, Thomson proposed that the indivisible atom was a uniformly distributed positively charged sphere, in which electrons were embedded. This proposal couldn't answer several of the questions raised about the plausibility of positively charged particles, stability of the atom and so on.

Becquerel's Mistake

The phenomenon of the luminescence of certain substances when exposed to sunlight is called fluorescence. The French scientist Henri Becquerel spent many years studying this phenomenon. Once he had observed a photographic film wrapped in a black paper and kept in a drawer was exposed. There was no way this could have happened because the substance (sulphate salt of potassium and uranium) he used could have fluoresced in the darkness of the drawer. When he studied more carefully the reasons for the same, he could establish that the binary salt of uranium and potassium emitted invisible rays that could expose the photographic film even in darkness. Thus, 26 February 1896, marked the discovery of a new physical phenomenon which became the starting point of the whole of new physics of the 20th century. It is interesting to note that all of the physics that followed started from this accidental observation. More to come in the articles to follow…

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