by John Carey
‘This pen will trace a line indicating the intensity of the radiation. When the pile chain-reacts, the pen will trace a line that will go up and up and that will not tend to level off. In other words, it will be an exponential line.
‘Presently we shall begin our experiment. George will pull out his rod a little at a time. We shall take measurements and verify that the pile will keep on acting as we have calculated.
‘Weil will first set the rod at thirteen feet. This means that thirteen feet of the rod will still be inside the pile. The counters will click faster and the pen will move up to this point, and then its trace will level off. Go ahead, George!’
Eyes turned to the graph pen. Breathing was suspended. Fermi grinned with confidence. The counters stepped up their clicking; the pen went up and then stopped where Fermi had said it would. Greenewalt gasped audibly. Fermi continued to grin.
He gave more orders. Each time Weil pulled out some more, the counters increased the rate of their clicking, the pen raised to the point that Fermi predicted, then it levelled off.
The morning went by. Fermi was conscious that a new experiment of this kind, carried out in the heart of a big city, might become a potential hazard unless all precautions were taken to make sure that at all times the operation of the pile conformed closely with the results of the calculations. In his mind he was sure that if George Weil’s rod had been pulled out all at once, the pile would have started reacting at a leisurely rate and could have been stopped at will by reinserting one of the rods. He chose, however, to take his time and be certain that no unforeseen phenomenon would disturb the experiment.
It is impossible to say how great a danger this unforeseen element constituted or what consequences it might have brought about. According to the theory, an explosion was out of the question. The release of lethal amounts of radiation through an uncontrolled reaction was improbable. Yet the men in the Squash Court were working with the unknown. They could not claim to know the answers to all the questions that were in their minds. Caution was welcome. Caution was essential. It would have been reckless to dispense with caution.
So it was lunch time, and, although nobody else had given signs of being hungry, Fermi, who is a man of habits, pronounced the now historical sentence:
‘Let’s go to lunch.’
After lunch they all resumed their places, and now Mr Greenewalt was decidedly excited, almost impatient.
But again the experiment proceeded by small steps, until it was 3.20.
Once more Fermi said to Weil:
‘Pull it out another foot’; but this time he added, turning to the anxious group in the balcony: ‘This will do it. Now the pile will chain-react.’
The counters stepped up; the pen started its upward rise. It showed no tendency to level off. A chain reaction was taking place in the pile.
In the back of everyone’s mind was one unavoidable question.
‘When do we become scared?’
Under the ceiling of the balloon the suicide squad was alert, ready with their liquid cadmium: this was the moment. But nothing much happened. The group watched the recording instruments for 28 minutes. The pile behaved as it should, as they all had hoped it would, as they had feared it would not.
The rest of the story is well known. Eugene Wigner, the Hungarian-born physicist who in 1939 with Szilard and Einstein had alerted President Roosevelt to the importance of uranium fission, presented Fermi with a bottle of Chianti. According to an improbable legend, Wigner had concealed the bottle behind his back during the entire experiment.
All those present drank. From paper cups, in silence, with no toast. Then all signed the straw cover on the bottle of Chianti. It is the only record of the persons in the Squash Court on that day.
Source: Laura Fermi, Atoms in the Family: My Life with Enrico Fermi, Designer of the First Atomic Pile, London, Allen Unwin, 1955.
A Death and the Bomb
Arch-enemy of gobbledegook and obscurity, Nobel Prize-winner Richard Feynman (1918–88) excelled at making science clear to the unscientific. The two books of memoirs and conversations compiled by Ralph Leighton, Surely You’re Joking, Mr Feynman and What Do You Care What Other People Think? reveal a defiantly individual, iconoclastic personality, distrustful of ‘intellectuals’. He once said that he would be just as happy if his children turned out to be truck-drivers or guitar-players, rather than scientists.
His main scientific work was to remake the theory of quantum electrodynamics (QED, for short) which explains the interaction of light (photons) and matter (electrons). Almost all natural phenomena, including all chemistry and biology, are covered by this theory. Explaining it to the general reader (in QED: The Strange Theory of Light and Matter), he begins, typically, with a familiar experience. Everyone knows that light is partially reflected from some surfaces – glass, for example. If you have a lamp in your room in daytime, and look out of the window, you can see things outside plus a dim reflection of your lamp. The fact that the lamp is partially reflected means that some photons (light particles) are bounced back by the electrons in the glass, while others pass through. Experiment shows that for every 100 photons an average of 4 bounce back, 96 go through. No one knows why. No one knows how a photon ‘makes up its mind’ which course to follow. No one can predict which course a given photon will opt for. Science can only work out the percentage probability.
The simple, graphic quality of this example is persistently evident in all Feynman’s writing – about life or science. In the Second World War he worked at Los Alamos on the atom bomb project. His wife Arlene was dying of TB of the lymphatic gland. They had known she was fatally ill when they married. He took leave from the project, drove to the hospital, and was there when she died. Afterwards, he kissed her:
I was very surprised to discover that her hair smelled exactly the same. Of course, after I stopped and thought about it, there was no reason why her hair should smell different in such a short time. But to me it was a kind of shock, because in my mind, something enormous had just happened – and yet nothing had happened.
Arlene’s death was followed by the successful testing of the first atomic bomb in the Nevada desert on 16 July 1945, recalled by Feynman in Surely You’re Joking:
After we’d made the calculations, the next thing that happened, of course, was the test. I was actually at home on a short vacation at that time, after my wife died, and so I got a message that said, ‘The baby is expected on such and such a day.’
I flew back, and I arrived just when the buses were leaving, so I went straight out to the site and we waited out there, twenty miles away. We had a radio, and they were supposed to tell us when the thing was going to go off and so forth, but the radio wouldn’t work, so we never knew what was happening. But just a few minutes before it was supposed to go off the radio started to work, and they told us there was twenty seconds or something to go, for people who were far away like we were. Others were closer, six miles away.
They gave out dark glasses that you could watch it with. Dark glasses! Twenty miles away, you couldn’t see a damn thing through dark glasses. So I figured the only thing that could really hurt your eyes (bright light can never hurt your eyes) is ultraviolet light. I got behind a truck windshield, because the ultraviolet can’t go through glass, so that would be safe, and so I could see the damn thing.
Time comes, and this tremendous flash out there is so bright that I duck, and I see this purple splotch on the floor of the truck. I said, ‘That’s not it. That’s an after-image.’ So I look back up, and I see this white light changing into yellow and then into orange. Clouds form and disappear again – from the compression and expansion of the shock wave.
Finally, a big ball of orange, the center that was so bright, becomes a ball of orange that starts to rise and billow a little bit and get a little black around the edges, and then you see it’s a big ball of smoke with flashes on the inside of the fire going out, the heat.
All this took about one minute. It was a series fro
m bright to dark, and I had seen it. I am about the only guy who actually looked at the damn thing – the first Trinity test. Everybody else had dark glasses, and the people at six miles couldn’t see it because they were all told to lie on the floor. I’m probably the only guy who saw it with the human eye.
Finally, after about a minute and a half, there’s suddenly a tremendous noise – BANG, and then a rumble, like thunder – and that’s what convinced me. Nobody had said a word during this whole thing. We were all just watching quietly. But this sound released everybody – released me particularly because the solidity of the sound at that distance meant that it had really worked.
The man standing next to me said, ‘What’s that?’
I said, ‘That was the Bomb.’
The man was William Laurence [author of Dawn Over Zero]. He was there to write an article describing the whole situation. I had been the one who was supposed to have taken him around. Then it was found that it was too technical for him, and so later H. D. Smyth came and I showed him around. One thing we did, we went into a room and there on the end of a narrow pedestal was a small silver-plated ball. You could put your hand on it. It was warm. It was radioactive. It was plutonium. And we stood at the door of this room, talking about it. This was a new element that was made by man, that had never existed on the earth before, except for a very short period possibly at the very beginning. And here it was all isolated and radioactive and had these properties. And we had made it. And so it was tremendously valuable.
Meanwhile, you know how people do when they talk – you kind of jiggle around and so forth. He was kicking the doorstop, you see, and I said, ‘Yes, the doorstop certainly is appropriate for this door.’ The doorstop was a ten-inch hemisphere of yellowish metal – gold, as a matter of fact.
What had happened was that we needed to do an experiment to see how many neutrons were reflected by different materials, in order to save the neutrons so we didn’t use so much material. We had tested many different materials. We had tested platinum, we had tested zinc, we had tested brass, we had tested gold. So, in making the tests with the gold, we had these pieces of gold and somebody had the clever idea of using that great ball of gold for a doorstop for the door of the room that contained the plutonium.
Source: Surely You’re Joking, Mr Feynman. Adventures of a Curious Character, Richard P. Feynman. As told by Ralph Leighton, ed. Edward Hutchings, London, Unwin Hyman, 1985.
The Story of a Carbon Atom
Born in Turin in 1919, Primo Levi graduated in chemistry shortly before the Fascist race laws prohibited Jews like himself from taking university degrees. In 1943 he joined a partisan group in northern Italy, was arrested and deported to Auschwitz. His expertise as a chemist saved him from the gas chambers, however. He was set to work in a factory, and liberated in 1945.
His memoir The Periodic Table takes its title from the table of elements, arranged according to their atomic mass, which was originally devised by Dmitri Mendeleyev in 1869 (see p. 148). Levi links each episode of his life to a certain element. But in the book’s final section, printed below, he sets himself to imagine the life of a carbon atom. This was, he says, his first ‘literary dream’, and came to him in Auschwitz.
Our character lies for hundreds of millions of years, bound to three atoms of oxygen and one of calcium, in the form of limestone: it already has a very long cosmic history behind it, but we shall ignore it. For it time does not exist, or exists only in the form of sluggish variations in temperature, daily or seasonal, if, for the good fortune of this tale, its position is not too far from the earth’s surface. Its existence, whose monotony cannot be thought of without horror, is a pitiless alternation of hots and colds, that is, of oscillations (always of equal frequency) a trifle more restricted and a trifle more ample: an imprisonment, for this potentially living personage, worthy of the Catholic Hell. To it, until this moment, the present tense is suited, which is that of description, rather than the past tense, which is that of narration – it is congealed in an eternal present, barely scratched by the moderate quivers of thermal agitation.
But, precisely for the good fortune of the narrator, whose story could otherwise have come to an end, the limestone rock ledge of which the atom forms a part lies on the surface. It lies within reach of man and his pickax (all honor to the pickax and its modern equivalents; they are still the most important intermediaries in the millennial dialogue between the elements and man): at any moment – which I, the narrator, decide out of pure caprice to be the year 1840 – a blow of the pickax detached it and sent it on its way to the lime kiln, plunging it into the world of things that change. It was roasted until it separated from the calcium, which remained so to speak with its feet on the ground and went to meet a less brilliant destiny, which we shall not narrate. Still firmly clinging to two of its three former oxygen companions, it issued from the chimney and took the path of the air. Its story, which once was immobile, now turned tumultuous.
It was caught by the wind, flung down on the earth, lifted ten kilometers high. It was breathed in by a falcon, descending into its precipitous lungs, but did not penetrate its rich blood and was expelled. It dissolved three times in the water of the sea, once in the water of a cascading torrent, and again was expelled. It traveled with the wind for eight years: now high, now low, on the sea and among the clouds, over forests, deserts, and limitless expanses of ice; then it stumbled into capture and the organic adventure.
Carbon, in fact, is a singular element: it is the only element that can bind itself in long stable chains without a great expense of energy, and for life on earth (the only one we know so far) precisely long chains are required. Therefore carbon is the key element of living substance: but its promotion, its entry into the living world, is not easy and must follow an obligatory, intricate path, which has been clarified (and not yet definitively) only in recent years. If the elaboration of carbon were not a common daily occurrence, on the scale of billions of tons a week, wherever the green of a leaf appears, it would by full right deserve to be called a miracle.
The atom we are speaking of, accompanied by its two satellites which maintained it in a gaseous state, was therefore borne by the wind along a row of vines in the year 1848. It had the good fortune to brush against a leaf, penetrate it, and be nailed there by a ray of the sun. If my language here becomes imprecise and allusive, it is not only because of my ignorance: this decisive event, this instantaneous work a tre – of the carbon dioxide, the light, and the vegetal greenery – has not yet been described in definitive terms, and perhaps it will not be for a long time to come, so different is it from the other ‘organic’ chemistry which is the cumbersome, slow, and ponderous work of man: and yet this refined, minute, and quick-witted chemistry was ‘invented’ two or three billion years ago by our silent sisters, the plants, which do not experiment and do not discuss, and whose temperature is identical to that of the environment in which they live. If to comprehend is the same as forming an image, we will never form an image of a happening whose scale is a millionth of a millimeter, whose rhythm is a millionth of a second, and whose protagonists are in their essence invisible. Every verbal description must be inadequate, and one will be as good as the next, so let us settle for the following description.
Our atom of carbon enters the leaf, colliding with other innumerable (but here useless) molecules of nitrogen and oxygen. It adheres to a large and complicated molecule that activates it, and simultaneously receives the decisive message from the sky, in the flashing form of a packet of solar light: in an instant, like an insect caught by a spider, it is separated from its oxygen, combined with hydrogen and (one thinks) phosphorus, and finally inserted in a chain, whether long or short does not matter, but it is the chain of life. All this happens swiftly, in silence, at the temperature and pressure of the atmosphere, and gratis: dear colleagues, when we learn to do likewise we will be sicut Deus [like God], and we will have also solved the problem of hunger in the world.
But there
is more and worse, to our shame and that of our art. Carbon dioxide, that is, the aerial form of the carbon of which we have up till now spoken: this gas which constitutes the raw material of life, the permanent store upon which all that grows draws, and the ultimate destiny of all flesh, is not one of the principal components of air but rather a ridiculous remnant, an ‘impurity,’ thirty times less abundant than argon, which nobody even notices. The air contains 0.03 percent; if Italy was air, the only Italians fit to build life would be, for example, the fifteen thousand inhabitants of Milazzo in the province of Messina. This, on the human scale, is ironic acrobatics, a juggler’s trick, an incomprehensible display of omnipotence-arrogance, since from this ever renewed impurity of the air we come, we animals and we plants, and we the human species, with our four billion discordant opinions, our milleniums of history, our wars and shames, nobility and pride. In any event, our very presence on the planet becomes laughable in geometric terms: if all of humanity, about 250 million tons, were distributed in a layer of homogeneous thickness on all the emergent lands, the ‘stature of man’ would not be visible to the naked eye; the thickness one would obtain would be around sixteen thousandths of a millimeter.
Now our atom is inserted: it is part of a structure, in an architectural sense; it has become related and tied to five companions so identical with it that only the fiction of the story permits me to distinguish them. It is a beautiful ring-shaped structure, an almost regular hexagon, which however is subjected to complicated exchanges and balances with the water in which it is dissolved; because by now it is dissolved in water, indeed in the sap of the vine, and this, to remain dissolved, is both the obligation and the privilege of all substances that are destined (I was about to say ‘wish’) to change. And if then anyone really wanted to find out why a ring, and why a hexagon, and why soluble in water, well, he need not worry; these are among the not many questions to which our doctrine can reply with a persuasive discourse, accessible to everyone, but out of place here.