The Fantastic Power in the Atom
The sun has scarcely risen. Here and there its almost horizontal beams slip through the gaps in the eastern range of mountains, mountains like jagged teeth, purple, eroded, teeth, with sudden, unexpected gaps between. The mountain shadows stretch halfway across the barren plateau, apart from them, there is nothing to be seen, but a windswept, dawn-chilled desert.
Then the sun catches a slender mast in the exact centre, a silver needle, gleaming now in its beam, like a vertical strip of fluorescent lighting. Dwarfed though it is by the vastness of the plateau, the mast is a hundred feet high, and whipping in the wind.
The sun moves; the needle vanishes. It has seemed, in the few seconds it was visible, rather like a woman’s hat-pin, with a neat black bulge at the top. Were it not for this bulge, this blob, at the top, one could take it for a wireless transmitting aerial. A long-distance one: there are no listeners here.
At exactly five-twenty, the most terrifying and incomparably the biggest thunderstorm the world has ever known, breaks loose above the lonely plateau. A cloud shoots vertically up, one, two, five, seven miles into the sky, and a ball of solid fire, a million lightning flashes bundled into one, explodes. A noise louder than ever before heard on earth echoes away across the barren lands of New Mexico.
It is 16 July, 1945. Man has unleashed the atom. A new era has dawned with the sun over Alamagordo, an era which will lead either to unprecedented riches and prosperity for all the world, or to the total destruction of that world. Man himself holds the key.
But all this is in the future. For the moment it is enough for the scientists, watching and measuring through systems of mirrors ten miles away, to know that the Second World War, which had bled mankind for almost six long years, is as good as over. For there are three of these terrifying devices, or were until a moment ago, and the United States possesses them all. Within a month the second will drop on the Japanese city of Hiroshima, destroying it completely, with thousands of its inhabitants; days later, the third will do the same for Nagasaki.
Atomos, the Undivided. So the Greeks called it, and the name Atom has persisted, even though we know the atom can be divided, torn down into its separate components, rebuilt in another form. The dividing of the undividable has in fact become almost a commonplace, and at the same time, the greatest single practical development in Physics, and in Chemistry, just as Einstein’s Theory of Relativity, closely related to it, is the greatest theoretical stride forward since the time of Newton.
Till the end of the nineteenth century, scientists were able to regard the atoms of the various elements as completely stable particles. It was true that hydrogen was a very different substance to copper, that mercury bore little resemblance to sulphur or iron, and that therefore the internal arrangements of their atoms, the hydrogen atom, the copper atom, those of mercury, sulphur and iron, must be different, one from the other. Yet no power on earth could take those atoms apart, to find out what went on inside.
Then, in 1902, Ernest Rutherford, the New Zealand-born scientist, showed that various heavier elements like uranium, thorium and radium, which had been observed to emit a kind of radiation, like the luminous hands of a watch, were in fact breaking up to form atoms of a different sort. Uranium and the others, then, were not stable; they broke up, spontaneously, formed other elements.
The old dream of the alchemist was revived. If this transmutation could happen with a few, little-known, elements, could not, for example, lead be turned into gold, iron into silver?
To Ernest Rutherford, though the thought was amusing, there seemed more to his discovery than this. He pressed on over the years, forcing the atom to give up, one by one, its closely guarded secrets. Many scientists have been involved in atomic research, but it is Ernest Rutherford, later Baron Rutherford, he died in 1937— to whom we owe credit for most of what we now know.
In 1895 the young New Zealander had won a scholarship to Cambridge and went to work there under the famous Professor J. J. Thomson in the new and splendid Cavendish Laboratory. It was an exciting time to start: a month after Rutherford put on his white overall for the first time, W. K. Rontgen produced in the laboratory a form of radiation, which for want of a better name he called an “X-ray”, and which seemed to penetrate all but the heaviest matter. If he placed his hands on a piece of photographic film, in the dark, and then directed these rays downwards on to the hand, he found he had taken an astonishing picture of the Inside of the hand, bones, flesh and all.
Then, a few months later, A. H. Becquerel showed that uranium compounds produced, spontaneously, radiation much like Rontgen’s rays. A year later, Thomson himself proved the existence of the long-suspected electron. Now the theory which men like Thomson and Rutherford had nursed for so many years, that all matter had a common origin, was built, as it were, from the same tiny and identical bricks, became a probability. The atom itself must be composed of these tiny electrical charges, but as the electron had been shown to be, always, negatively charged and to move in the direction of any positively charged object, like the positive pole of a battery, whereas the atom normally had no charge, it was obvious to Rutherford that these electrons must be balanced, within the atom, by other, positively charged, particles. It was some years before he established the fact, with his Nuclear Theory.
In the meantime he went on from Cambridge to Canada, where he had been offered, at the age of twenty-seven,, a Professorship at McGill University. His fame spread and soon young men from all over the world came to McGill to work with him. One of the most brilliant was the Englishman Frederick Soddy, and with his help Rutherford in 1902 put forward the revolutionary theory that “radio-activity is a phenomenon accompanying the spontaneous transformation of atoms of radio-active elements into a different kind of matter”. He based his theory on the observation that radioactivity was quite unaffected by heat, cold or chemicals, and the vastly more important one, which ultimately produced the bomb, that “radio-active change is accompanied by an emission of heat of a quite different order of magnitude from that accompanying chemical reactions”.
In fact, as was later proved, each atom produced three million times the energy it might have yielded in a chemical reaction like burning. The new theory was treated with scepticism: it cut right across the long-held theory that all matter is indestructible. Then, three years later, in 1905, Albert Einstein, in a deduction from his Theory of Relativity, showed that there is no essential difference between Mass and Energy and that, as Rutherford had stated, the transformation of a very small Mass would result in the production of huge quantities of Energy.
In 1907, Rutherford decided to accept an offer to return to England and work in what was considered the world’s most up-to-date laboratory, the new one at Manchester University. Here he proved that one of the three forms of radiation emitted by radioactive elements (which had been given the names of alpha, beta and gamma radiation from the first three letters of the Greek alphabet), the radiation of alpha rays, was in fact a stream of actual atoms. The heavy, radio-active, element radium was emitting a high-speed stream of atoms of a lighter element, helium, and these were positively charged, as if one or more electrons had been removed. He showed that 136,000 of these helium atoms were ejected every second from one thousandth of a gramme of radium. In an experiment with a piece of radium sealed into a thick glass tube he was able to show the helium arriving as if by magic on the outside of it.
As in Canada, he found men flocked to join him, work under him, and with their help in Manchester he was able, in 1910, to propound his Nuclear Theory, that nearly all the Mass of an atom is in the nucleus, the small, dense centre, and that this is positively charged, with positive “protons” balancing the negative charges of the electrons circling, at a relatively great distance, around this nucleus. The alpha particles from radio-active elements could, if they collided directly with the nucleus of any atom, transform that atom into a different one, by altering the number of its electrons and the balancing “protons” which were in the nucleus. But as Rutherford had shown, alpha particles have a positive charge and they are therefore repelled by the positively charged nucleus. For this reason very few of them, however forcibly they are emitted, succeed in penetrating an atomic nucleus.
Then in the 1930s the scientist Chadwick and others showed that if neutral particles, carrying no charge, which were believed to exist within the nucleus, alongside the protons, could be isolated and used to bombard an atom, they would not be repulsed by either the positive nucleus nor the circling, negatively charged, electrons surrounding it. When a neutron struck an atom it would pass through these “planetary” electrons and right into the nucleus , if it were aimed correctly.
Neutrons, because they could not be attracted in any way, by either positive or negative forces, were hard to obtain, but eventually it was done, and a whole new field of “atom-smashing”, by “neutron-bombardment”, was opened up. But, until 1939, though the term “atom-smashing” was used, man had only succeeded in knocking out one, two, perhaps four, particles. Then in that year a German woman scientist, Lise Meitner, discovered that if uranium were bombarded by neutrons, the uranium atom appeared to be actually splitting, breaking in half.
Scientists all over the world repeated her experiment, proved it correct. A new kind of nuclear behaviour had been discovered,! the nucleus was not merely being chipped it was being spin. The behaviour was named “fission”.
Soon, experiment showed that a rare form of uranium, given by scientists the number 235, to distinguish it from the more common uranium-238, would split extremely easily. Calculation showed that every uranium-235 nucleus that underwent fission would produce seven thousand times the energy of the neutron that made it break in two.
But this was only the beginning. Heavy nuclei need neutrons to keep them together (the lighter ones, like that of hydrogen, have no neutrons at all). When a massive uranium-235 nucleus breaks into halves, it no longer requires all its neutrons. Not only does the break-up produce, as we have seen, seven thousand times the energy of the neutron that caused it, but it liberates two or three neutrons to go on and do exactly the same thing to other nuclei, and so on.
The “chain reaction” producing the enormous destructive energy of the atomic bomb. And, properly controlled, the slower, longer-lasting energy of the nuclear powerstation.
But, even in 1941, this, though understood, was only a pipe-dream. Then Albert Einstein wrote President Roosevelt that, with the United States now in the war, she could not allow the enemy to develop this possibility of uranium fission into a weapon. She must do it first.
Roosevelt, and the British Government which had encouraged a good deal of independent research into the matter, agreed wholeheartedly and the “Manhattan Project” was born: a secret research programme, costing over its three and a half years some two thousand million dollars, and culminating, in July, 1945, with the test bomb over New Mexico. The problems were immense. It had been discovered that fission went on spontaneously in the rare uranium-235, but that, fortunately for the experimenters, most of the neutrons liberated in a small piece of it found their way through its sides without striking nuclei. There must, though, be a “critical size”, when the quantity of uranium was so great that there would be enough neutrons hitting nuclei to allow the chain reaction to proceed, become self-supporting.
The critical size was calculated. Then, a sufficiently large quantity of 235 had to be separated from uranium-238, an immensely complicated and slow process. Now if two pieces of 235, smaller than the critical size but, together, larger, could be pushed together, the chain reaction would begin, the bomb would explode, go on exploding until all the uranium-235 had disappeared. But as the electron charges of the uranium atoms would tend to repel each other, the two pieces of 235 would have to be forced together at a speed approaching that of a bullet through the air.
They were. The bomb worked.
Since the bombs over New Mexico, Hiroshima, Nagasaki, a newer and much more powerful weapon has been developed, using, like this fission-bomb, a nuclear reaction. Scientists had long believed that if it were possible, instead of breaking down a heavy atom, to make two light ones fuse together, the amount of energy released would be far greater. Notwithstanding Rutherford’s theory that radio-activity was not affected by heat, it was believed that the millions of degrees which were produced by atomic fission might force light atoms, like those of hydrogen, to fuse together and form heavier ones, like those of helium.
This was so, and within a few years the United States, using an “ordinary” atomic bomb as a trigger, had detonated its first hydrogen bomb over the Pacific. A few years after that, the Russians had developed their own and the two great powers could sit back, conscious that each had power to wipe out the other, that one “H-bomb” from either side could destroy most of a city, and that, apart from the blast and the heat which would do the initial damage, there was the third, insidious threat of “fall-out”, when the products of fission and fusion, deadly gamma rays, began to settle earthwards after the bang. These would be likely to wipe out even more of a population than the other two. And if the hydrogen bomb were encased in the element cobalt, the fall-out would be many times more lasting, more lethal. It wasn’t hard to see that a very few bombs might wipe out the whole of the human race.
For the first time in history, man had to consider the ultimate wisdom of war, war which he might win or lose, but which, in either case, might destroy him and his descendants for ever.
Better perhaps to sit in peace, in the light of a hydrogen bomb 93,000,000 miles away. For that, he now discovered, was the source of his sunlight. The reason the sun never “burnt out”, as scientists for a thousand years had predicted it would, was that it was one vast and continuing hydrogen bomb explosion, with the release of huge quantities of heat and light caused by the loss of only a very small amount of matter, leaving enough to warm him for millions and millions of years to come.
Better sit back and enjoy it.
- Annotated bibliography for neutrons from the Alsos Digital Library for Nuclear Issues
- Abraham Pais, Inward Bound, Oxford: Oxford University Press, 1986. ISBN 0198519974.
- Herwig Schopper, Weak interactions and nuclear beta decay, Publisher, North-Holland Pub. Co., 1966. OCLC 644015779
- Ruth Lewin Sime, Lise Meitner: A Life in Physics, Berkeley, University of California Press, 1996. ISBN 0520208609.
- Roger H. Stuewer, “The Nuclear Electron Hypothesis”. In Otto Hahn and the Rise of Nuclear Physics, William R. Shea, ed. Dordrecht, Holland: D. Riedel Publishing Company. pp. 19–67, 1983. ISBN 90-277-1584-X.
- Sin-Itiro Tomonaga, The Story of Spin, The University of Chicago Press, 1997. ISBN 9780226807942