A FAMOUS NEW ZEALANDER

Evening Star, Issue 19062, 3 October 1925, Page 24

A FAMOUS NEW ZEALANDER

, —>■ THE WONDERFUL ATOM SIS E. SUTHESFORS'S RESEARCHES [Written by Professor D. C. H. Flobance', for tlio ‘Evening Star.’J No. IT. Of all the wonderful discoveries that have been made in applied physics during tho past thirty years, mine are more ■wonderful than those which have been made in connection with tho constitution and structure of tho atoms of | matter. Tho physical properties oi llie j atoms used to be approximately ex- ! plained by assuming that the atoms were hard little spheres, all tho atoms of one element being identical with one another, and different from those of any other element. Scientific thought received a shock when Professor Sir Ernest Rutherford first put forward tlurscnsatioual theory that atoms of matter were not the permanent, structures that people had become a* customed to believe, but wore in reality j complex systems, and certain clcmonis ! of which radium is a well-known type wore in a continual state of spontaneous disintegration. Still more striking j was his later achievement of knocking; the atoms to pieces and of seeing wind they were built oi. Our present knowledge of the atom is due primarily to I l,he intuition and experimental skill of J Professor Sir Ernest Rutherford, 0.51.. I F.R.S., who is visiting his native land, I and is giving an account of his cpoch- ; making discoveries. | The problem of taking an atom to pieces is most certainly a tricky one. j Tho radius of an atom of hydrogen is of i the order one hundred millionth of I a centimetre, and its mass is about 1.66 xlO to the power of Although the hydrogen atom is the Tightest of the . elements, I there is something still lighter; lit is tho electron, whoso mass i is l-1850th that of tho hydrogen atom. ; It is a negatively charged particle, and ' tho charge it carries is tho smallest Charge known. Electrons are mm known to pervade tho universe, and (heir size has nothing to do with their importance. Abundant evidence of their importance is given by the part they play in wireless telegraphy, and in X-ray production. An electron can bo easily detached from a hydrogen atom, leaving behind a core which is sometimes called the hydrogen nucleus, or more usually by the name applied to it by Sir I. nest Rutherford—tho proton. It carries the smallest unit of positive charge, equal in magnitude to that of tho electron. It seems certain that every element in the universe is built up of those two fundamental units—the proton, representing the brick, and the electron, representing the cement by means of which all material things are constructed. How was Sir Ernest Rutherford led to take this view of matter? Tho key to this new world of wonders was the phenomenon of radio-activity. Radioactive substances possess tho remarkable property of spontaneously emitting energy and changing into now forms of matter. The atom sometimes explodes with tremendous violence, and a positively-charged particle is hurled out with a velocity of 20,000 miles a second. This atomic projectile is four times as heavy as an atom of hydrogen. It is called an alpha particle. In some cases a negatively-charged particle is ejected with a velocity "renter than 100,000 miles a second. This particle . has been called a beta particle, and is identical with the electron. Besides the alpha and beta particles radioactive substances emit radiant energy in the form of gamma rays, which differ from X-rays only in this respect, that they are of much shorter wavelength and are therefore much more penetrating. When alpha particles strike a suitable phosphorescent screen they produce minute flashes of light. Here we observe the action of one atom at a time. By counting these scintillations Sir Ernest was able to calculate the exact number of atoms contained in a given quantity of matter, Moreover, by collecting the alpha particles in a previously-evacuated vessel, he showed that they were in reality atoms of helium. Where did this atom of helium originate? Sir Ernest suggested that it undoubtedly came from within the radio-active atom, and that there must be a mighty supply of energy in the atomic gun to give this projectile such an enormous velocity. Mass for mass the energy of the projectile is four hundred million times greater than that possessed by a rifle bullet. It was clear then that tho atoms of the radio-active elements, at least, contained positively-charged particles four times the mass of tho hydrogen atom, and ncgaticely-charged particles l-1850th the mass of the hydrogen atom. How these particles were arranged and whether other atoms contained the same constituents no one know. Once more Sir Ernest boldly attacked the problem. Since alpha particles are the most energetic of all projectiles, he conceived the idea of bombarding. and smashing to bits the atoms of suitable elements which were to serve as targets. These targets are inconceivably small, but he had an unlimited supply of bullets, and it seemed quite reasonable to expect that at least one of every million alpha particles would secure a direct; hit. He was not mistaken. A certain proportion of these minute projectiles hit the atoms with such accuracy and with such violence that in some cases a portion was hurled out. Nor was this the only result obtained, for with the heavier elements the colliding alpha particle was sometimes itself hurled back in the direction .from whence it had come. From this experiment was evolved Mio famous Rutherford atom. Sir Ernest made the suggestion that the mass of tho atom is concentrated as a impious which is exceedingly small compared with' the atom itself. The atom is a veritable solar system in miniature. Briefly, the facts are these. All the positive electricity in the form of protons is contained in tho nucleus, which contains practically all the mass of the atom. In most cases tho nucleus contains electrons as well, but the protons always outnumber tho electrons. The nucleus corresponds to our sun. Around tho nucleus wo have electrons revolving in orbits, whose radii are very great compared with the radius of the nucleus. These electrons correspond to the planets of our solar system, and the atoms, instead of being hard and impenetrable, are in comparison as empty as the solar system. This accounts for the fact that an atom of helium can for a certain fraction of a second exist within the atom ol another element. Sir Ernest Rutherford has not only shown us the wonderful structure of the atom, hut has also ■ succeeded in breaking up the atom . for . the first time, and he lias made it evident that' the whole universe is. built up of the two fundamental units—-protons and electrons. He is now .elucidating tho inner secrets of the lindens. “ Lo, these are parts of His ways, hut how little a portion is heard of Him.”