Destroyer of Worlds
FRANK CLOSE
Destroyer of Worlds
The Deep History of the Nuclear Age
1895–1965
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List of Illustrations
p. 101 Neutron Discovery: Kapitza Club talks by N. Feather 26 January and J. Chadwick 23 February 1932. Churchill Archives Centre, The Papers of Sir John Cockcroft, CKFT 7/1.
Inset
1. Henri Becquerel, 1896. Atelier Nadar. Bibliothèque nationale de France.
2. H. Becquerel, Recherche sur une propriété nouvelle de la matière, Paris: Firmin Didot, 1903; plate 1, No.2. Wellcome Library, London CC BY-NC 4.0.
3. H. Becquerel. Discovery that uranium emits radiation spontaneously. Recherche sur une propriété nouvelle de la matière, Paris: Firmin Didot, 1903; plate 1, No.1. Wellcome Library, London CC BY-NC 4.0.
4. Wilhelm Conrad Röntgen, circa 1900. Mansell/The LIFE Picture Collection/Shutterstock.
5. First medical X-ray by Wilhelm Röntgen of his wife – Anna Bertha Ludwig’s – hand, in 1895. Photoprint from radiograph by W. K. Röntgen, 1895. Wellcome Collection 32971i.
6. Ettore Majorana and his family. Courtesy of Professor Ettore Majorana.
7. Niels Bohr lectures in Copenhagen, April 1929. Photograph by Samuel Goudsmit, courtesy of AIP Emilio Segrè Visual Archives, Goudsmit Collection.
8. Via Panisperna boys photographed by Bruno Pontecorvo. Courtesy of Sapienza University of Rome, Physics Department Archives,
Lodovico Zanchi Archive, Ser. 7, file 3, subfile 1, Istituto di via Panisperna.
9. Pierre and Marie Curie with daughter Irène. Circa 1902. Atomic Heritage Fund.
10. Marie and Piere Curie in their laboratory in Paris. Atomic Heritage Fund.
11. Ernest Rutherford as a young man. Science Photo Library, Professor Peter Fowler.
12. J. J. Thomson photographed for the Supplement to the ‘Gownsman’ 21st October 1909. Courtesy of the Cavendish Laboratory, University of Cambridge.
13. Ernest Rutherford with Hans Geiger at the University of Manchester, 1911. Supplied under licence by the United Kingdom Atomic Energy Authority (UKAEA). Copyright owned exclusively by UKAEA. All rights reserved [2025].
14. Ernest Marsden, photographed in 1921. S P Andrew Ltd: Portrait negatives. Ref: 1/2-043316-F. Alexander Turnbull Library, Wellington, New Zealand. /records/22538710.
15. A group of scientists at the 7th Solvay Conference, Brussels, October 1933. © The Regents of the University of California, Lawrence Berkeley National Laboratory. Photographer: Donald Cooksey.
16. Lise Meitner and Otto Hahn, Dahlem, Germany, 1913. Acc. 90-105 – Science Service, Records, 1920s–1970s, Smithsonian Institution Archives.
17. Ida Noddack in her laboratory at the University of Freiburg, standing in front of her X-ray spectrograph. Courtesy of University Archives, KU Leuven, Archive Walter and Ida Noddack-Tacke, nr. 51.
18. Ernest Walton in the counting house of the Cockcroft Walton accelerator 1932. Courtesy of the Cavendish Laboratory, University of Cambridge.
19. J. Cockroft, Ernest Rutherford, and Ernest Walton outside the Cavendish Laboratory, Cambridge University, circa 1932. Supplied under licence by the United Kingdom Atomic Energy Authority (UKAEA). Copyright owned exclusively by UKAEA. All rights reserved [2025].
20. Frédéric and Irène Joliot-Curie, circa 1935. Copyright Société Français de Physique, Paris, courtesy AIP Emilio Segrè Visual Archives, gift of Jost Lemmerich.
21. Young Ernest Lawrence and the prototype cyclotron. © The Regents of the University of California, Lawrence Berkeley National Laboratory. Photographer Roy Kaltschmidt.
22. Ernest Lawrence and Milton Stanley with the 27-inch prototype cyclotron. © The Regents of the University of California, Lawrence Berkeley National Laboratory.
23. Hans Bethe at the blackboard, 1956. © Edith Michaels. Niels Bohr Library & Archives / AIP Emilio Segré Visual Archives.
24. William Penney, Otto Frisch, Rudolf Peierls and John Cockcroft awarded the US Presidental Medal of Freedom 1947. Courtesy Los Alamos National Laboratory.
25. Albert Einstein and J. Robert Oppenheimer photographed at Princeton University in 1947. Alfred Eisenstaedt/The LIFE Picture Collection/Shutterstock.
26. Leo Szilard, photographed after the Soviet Union exploded its first atomic (fission) bomb, 1949. Argonne National Laboratory.
27. John von Neumann, Richard Feynman and Stanislaw Ulam sitting on a bench talking during the Nuclear Physics Conference in August of 1946. Courtesy Los Alamos National Laboratory.
28. John von Neumann and J. Robert Oppenheimer stand together in front of the computer, circa 1952. © Alan Richards, Courtesy of the Shelby White and Leon Levy Archives Center, Institute for Advanced Study (IAS).
29. Atom Bomb Trinity Test: Three time lapse images: 25/1000 seconds; 8 seconds; 60 seconds. July 16, 1945. Trinity Site, Alamogordo Test Range, Jornada del Muerto desert. Courtesy Los Alamos National Laboratory.
30. US nuclear weapon test Ivy Mike, 31 Oct 1952, on Enewetak Atoll in the Pacific. The US Department of Energy.
31. Portrait of Yakov Zeldovich. AIP Emilio Segrè Visual Archives, Physics Today Collection.
32. Yulii Khariton near the body of the RDS-1 bomb. Museum of Nuclear Weapons RFNC-VNNIEF.
33. Andrei Sakharov and Igor Kurchatov taking a break outdoors at the Institute of Atomic Energy, 1958. Courtesy of Marina Sakharov / Sakharov Family Archive.
34. Andrei Sakharov and Vitaly L. Ginzburg at the Department of Lebedev’s Physics Institute (FIAN ) Moscow, 1988. Courtesy of Marina Sakharov / Sakharov Family Archive.
35. Edward Teller as the director of Lawrence Livermore National Laboratory, circa 1958. Courtesy of Lawrence Livermore National Laboratory.
36. Tsar Bomba, USSR , 30th October 1962. Alamy Stock Photo.
prelude
Trinity 1945
On the evening of 15 July 1945, a fleet of military buses set out from the nuclear laboratory at Los Alamos near Santa Fe in northern New Mexico. They were filled with four hundred scientists and technicians who for five years had been in a desperate race to make an atomic bomb before the Nazis or the Japanese. They were headed 250 miles south, to the Jornada del Muerto desert, where, under the cloak of darkness, they hoped to realise the fruits of their work.
Shortly after 2:00 a.m. the convoy reached its destination and disgorged its passengers, by now cold and stiff but also in a state of high excitement as they prepared for the first ever man-made nuclear explosion. In the darkness they could discern the faint glow of floodlights some 20 miles distant across the valley floor. Through binoculars the illumination revealed a 30-metre-tall tower, which in outline looked like a lone abandoned oil derrick made of steel. Suspended near its top was a bulbous container, which housed the bomb.
Up until this moment in history, explosions had been chemical in nature, ignited by a spark. The largest planned one had involved 150 tonnes of explosives detonated in 1885 by the US Army Corps of Engineers. The blast, which destroyed an entire island in the East River of New York City and cleared the way for shipping, was heard 50 miles away in Princeton, New Jersey. The calculations of the Los Alamos scientists predicted that the power of a nuclear explosion coming from a mere 6 kilogrammes of the element plutonium would be equivalent to more than 20,000 tonnes of dynamite – the weight of a battleship made of nitroglycerine. This would be in a different league entirely. If the test was successful, it would mean that a destructive power equivalent to five times the entire load dropped
over Dresden in 1943, which had taken three nights to accomplish and involved fourteen hundred heavy bombers, could in the future be delivered by a single plane carrying just one bomb.
At least that is what the theory implied; only experiment would show if this really worked. And there was much concern as to whether the calculations were to be believed. The temperature in the explosion would be tens of millions of degrees, far hotter than the heart of the sun, and some feared that this inferno might ignite the atmosphere. The theoretical physicists at Los Alamos had rechecked their calculations and assured the doubters that the atmosphere would survive. Trusting that no mistakes had been made in the arithmetic, the scientists now took their places in the desert and awaited to see what would happen.
At 5100 feet (1565 metres) above sea level, the desert night was cold. There had been storms overnight, but these had moved away. Stars twinkled through a cobweb of misty clouds, but flickers of lightning beyond the surrounding mountains and the occasional sounds of distant thunder still threatened to disrupt the test. The weather forecast predicted that this would clear within a couple of hours, and so the test was given the go-ahead for 5:30 a.m., shortly before dawn.1
The canister suspended in the tower contained slices of plutonium, a substance so unstable that it is no longer found naturally on Earth, all primaeval atoms of the element having long since decayed. As in the solar system Pluto lies beyond Uranus, so in the table of atomic elements is plutonium an outlier beyond uranium, the heaviest naturally occurring element. Plutonium, nearly twice as dense as lead, is radioactive, spontaneously converting into uranium and other more stable elements. The plutonium to be used in the bomb test had been created in nuclear reactors by bombarding uranium with neutrons. It had taken months to breed its 6 kilogrammes, one atom at a time. In small amounts plutonium degrades, releasing energy slowly, but if you bring enough together – surpassing what is known as the critical mass – plutonium will blow up of its own accord. This is not an ordinary explosion like TNT or dynamite where the outer reaches of atoms liberate chemical energy. It is the result of a sudden release of nuclear energy, energy that has been locked in the heart of atoms since before the Earth was born.2
Trinity 1945
To exceed the critical mass, the idea was for the pieces of plutonium, which were initially located safely near the surface of the spherical container, to implode, forming a supercritical mass at the centre. To make this happen, conventional explosives surrounded the sphere in the pattern of twelve hexagons and twenty pentagons often used to make footballs.
A small radioactive source inside the device spontaneously released neutrons, electrically neutral constituents of atomic nuclei. When one neutron hits the nucleus of a plutonium atom, it will split that nucleus in two, a process known as fission. Plutonium nuclei themselves contain neutrons; fission liberates both energy and two or three of those neutrons. If the plutonium sample is smaller than the critical mass, these neutrons will escape before they can induce further fissions, but for larger volumes above the critical mass, further collisions will take place, inducing more fissions and releases of energy. The first of these liberates energy and three more neutrons, which in their turn can hit further atoms, releasing more energy and a third generation of neutrons. This continues, producing a fourth generation, a fifth, and onwards such that within less than a thousandth of a second there is an exponential growth of neutrons and release of energy. The entirety will explode in less than the blink of an eye.
Shortly after 5:00 a.m. everyone was alerted by announcements on loudspeakers that the test was imminent. The countdown was broadcast. Now was the time to don dark goggles to counter a flash so bright it was expected to penetrate eyelids, plaster on sun cream to protect skin from radiation, and then lie prone in the sand facing away from the blast. A few seconds after 5:29 a.m., electric pulses travelling along miles of cable to the tower reached their destination: the explosive charges on the surface of the sphere. These detonated causing the shell to collapse, imploding the individual pieces of plutonium metal into a concentrated lump greater than the critical mass at the centre of the bomb.
Where moments earlier a radioactive source had produced neutrons which were effectively harmless, now, in the heart of the assembly where the plutonium had imploded, there was no escape for them. The unstoppable inferno began when one neutron set off one fission and immediately spawned a chain reaction, which flashed through the
compacted metal faster than lightning. Energy stored within the nuclei of plutonium atoms was released with an explosive power previously unknown on Earth. The force of the blast was billions of times stronger than atmospheric pressure, the temperature four times hotter than the heart of the sun. Nothing on Earth can withstand such conditions.
Miles away across the valley, not everyone had shut their eyes or lay facing away; some took a surreptitious peek at the distant tower. Those who did saw a momentary flash like a distant sunrise but as bright as high noon. Early risers in Tularosa, over the horizon 40 miles to the southeast, saw what appeared to be a premature dawn in the north, far from where a normal sunrise would happen. The blast emitted light over the entire range of the electromagnetic spectrum. The scientists, in groups positioned miles away from the explosion, saw the crevices and peaks of the surrounding mountains briefly illuminated by a strange greenish glow.
In addition to this flash of visible light, the multimillion-degree temperature of the blast radiated heat. This man-made artificial sun vaporised the metal tower and in an instant fused the surrounding desert sand into glass. A buoyant gas of shattered atoms rose rapidly, causing turbulent vortices to curl downwards around its edges. These formed a central column that drew up debris and condensed atmospheric vapour to form the stem of what looked like a gigantic mushroom, the first time such a thing had been seen.
Even after spreading 10 miles, the hotness scorched the watchers’ skin, one describing it as like ‘opening a hot oven door with the sun coming out like a sunrise’.3 The radiant blast also included X-rays and lethal gamma rays, light with higher energy than the visible spectrum. These invisible rays passed through the watchers’ sunscreen, penetrated their skin, and passed through their bodies. In that moment the intense flux broke strands of their DNA , causing genetic damage that years later would lead to catastrophic mutations and, in some cases, life-threatening cancers.
In many filmed renditions or newsreels of atomic blasts, the visual drama gains added intensity thanks to the simultaneous accompaniment of the deafening sounds of the explosion.4 That is not what the watchers lying 10 miles away experienced, however. They saw portents of the apocalypse, but in total silence.
This is because, whereas radiant heat, gamma rays, and the vision itself all travel at the speed of light and reached the observers in a mere instant, sound advances only 330 metres every second or a mile in about five seconds. So, for up to a minute the desert night remained quiet but for the cheers of the scientists. The hurrahs died as everyone took cover, the awesome vision of the cloud of radioactive debris already rising miles into the stratosphere forewarning them of what would arrive within less than a minute.
Watchers 10 miles away had envied those in the relative front row, some 6 miles from ground zero, but now the vision showed the blast to have been bigger than most had anticipated, and even 10 miles felt too close for comfort. A bang loud enough to shatter the eardrums was on its way, shortly to be followed by a tsunami of high-pressure air, the mechanical effect of the explosion, moving at about 500 miles an hour, blasting everything in its path with irresistible force.
Lying flat on the ground, heads away from the explosion, faces down, and hands over their ears, they felt the storm pass with a deafening boom. Debris flew past. The bang echoed from the valley walls, rolling back and forth, as for several minutes in a sonic form of radar the shock waves mapped mountain ranges up to 50 miles away. Meanwhile the mushroom cloud rose higher, its colour changing until its light subsided and, in the east, the red glow of the real dawn took over.
The nuclear age had arrived. It was 05:29 a.m. in New Mexico on 16 July 1945.
It’s little appreciated that there were three Industrial Revolutions.
The First Industrial Revolution was powered in the eighteenth century by the engineering genius of James Watt, the Scottish inventor who radically improved the power and efficiency of steam engines. The dynamo of the Second, which began in the nineteenth century, was Michael Faraday’s discovery at London’s Royal Institution of electromagnetic induction, a fundamental principle of electric motors. And a Third Revolution took place in the first half of the twentieth century when we discovered how to release the vast reserves of energy locked within the nuclei of atoms.5
Steam power involves water changing from liquid to vapour; the
mutual cohesion between water molecules – H 2 O – suddenly disappears at 100 degrees Celsius, but the individual atoms of hydrogen and oxygen in those molecules are unchanged. The first direct hints of activity within atoms themselves came at the cusp of the twentieth century when the detection of radioactivity and the atom’s constituent parts revealed the presence of a vast reservoir of atomic energy.
In 1897, the discovery of the electron identified the carrier of electricity, the source of magnetism, and the engine of the Second Revolution. Electrons are electrically charged particles that exist in the outer reaches of atoms. Electric current is the flow of electrons – through wires, liquids, and gases – which involves the disruption of atoms as they give up or receive electrons and reorganise themselves to enable free passage of the current. Chemistry is a result of electrons moving between atoms, reconfiguring their molecular combinations. Throughout history to this juncture, and well into the twentieth century, atoms and their electrons were the engines of science and industry. Yet in all of eighteenth- and nineteenth-century technology, the atomic nucleus was passive, a static lump of positive charge, the seed around which electrons whirl to build atoms.
There would have been no nuclear age had we not first discovered this hidden jewel and found that it too has an internal structure comprised of protons – massive positively charged particles – and their near-twins, neutrons – massive electrically neutral particles. Reorganise those constituents and energy can be released in amounts that are over a million times larger – atom for atom – than anything made available because of the first two Industrial Revolutions. This discovery, which marked the dawn of the Nuclear Age, coincided almost exactly with the start of the Second World War. Its empirical validation heralded the end of that conflict.
Of all the bricks in nature’s construction kit, the nucleus is the most deeply hidden. In our daily lives its only visible presence is the sun, a nuclear furnace converting six hundred million tonnes of hydrogen into helium every second.
The temperature in the sun’s centre where this alchemy takes place is about fifteen million degrees Celsius. Heat the environment to tens of millions of degrees, or focus the equivalent amount of energy, and the nucleus can be revealed. In Earth’s ambient conditions, however,
nuclei normally stay at atoms’ length, cloaked by a net of protective electrons. These electrons are the agents of chemistry, biology, and life, whereas the nucleus sits inert at the centre of their activity, occupying less than a trillionth of each atom’s volume. The effects of electrons are visible in electric sparks, lightning, and aurora, whereas radioactivity – the only natural output of the nucleus and the clue to its existence – remains hidden to normal senses. But for serendipity and the insights of genius, the atomic nucleus might have stayed long shrouded from us.
This first inkling of nuclear energy was so trifling that it was almost missed. Instead, the chance discovery in 1896 of faint smudges on a photographic plate in a closed unilluminated drawer inspired a quest to tap and control this new force of nature. Pursuit of this hidden power source began innocently and collaboratively only to be overtaken by world events in the 1930s as the spectre of fascism loomed. In exactly fifty years science solved how to liberate nuclear energy, delivering it in a steady stream as in a nuclear reactor, in the explosive blast of an atomic bomb, or in a ‘backyard’ thermonuclear weapon so powerful that there would be no need to move it from the construction site – as it could destroy all life on earth from anywhere.
For millennia nature had hidden the presence of the atomic nucleus from sight. The clues however were there, and it was in Germany, late one afternoon on a dank November day in 1895, that the saga began.
PART I
The Nucleus Revealed 1895–1913
1
The Third Revolution
By the mid-nineteenth century, science was beginning to make sense of the material world. The First Industrial Revolution, associated with steam engines, the development of thermodynamics, and the application of Newton’s laws of motion, was a century old. Solids, liquids, and gases, such as ice, water, and steam, were understood as made of many microscopic particles – atoms or molecules – in constant rapid motion. The scientists of the day agreed that the average kinetic energy of these particles determines the temperature of the ensemble, their increasing agitation as temperature rises first breaking the frozen grip of ice and ultimately the more fluid bonds of water to liberate the molecules of steam. This kinetic theory of heat was a physical link between thermodynamics and the atomic world.
Chemistry was an established science with atoms as its foundation. All atoms of a given element were believed to be identical, indestructible, and impenetrable, something like miniature billiard balls. Individual atoms of one or more elements join to form molecules. These chemical combinations enabled scientists to determine the atomic masses of different elements relative to that of hydrogen, the lightest, at 1 atomic mass unit (AMU ). For example, a molecule of water, H2O, weighing in at about 18 AMU shows oxygen to have an atomic mass of 16 AMU , and carbon dioxide and nitrogen compounds then determine carbon’s and nitrogen’s magnitudes to be 12 and 14 AMU , respectively.1
In 1869, when the Russian Dmitri Mendeleev listed the known elements in the order of their atomic masses, he noticed that similar chemical properties appeared with periodic regularity. This led to his periodic table in which he placed elements with similar properties in
columns, with the lightest at the top and heaviest at the bottom, and then placed columns side by side in sequence of their relative masses.2 This alignment created a gallery of elements arranged like an advent calendar, but with gaps. Mendeleev predicted these vacancies would be filled by yet undiscovered elements, a vision that was dramatically confirmed by the discoveries between 1875 and 1886 of gallium, germanium, and scandium in, respectively, France, Germany, and Sweden. At the time of Mendeleev’s periodic table, only sixty-two elements were known, the two heaviest being thorium and uranium with atomic weights then determined as 231 and 240 AMU , respectively.3 Sufficient of their chemical properties were established for Mendeleev to place uranium in a column separated by a gap from that containing thorium. Mendeleev’s scheme thereby implied there exists an element between them, which he named eka-tantalum, meaning one place below the element tantalum in the intervening column.
Atoms were the basic bricks of the substances that powered the First Industrial Revolution. Electric and magnetic forces, the cement that builds material structures from those bricks, were heralds of the Second.
The pulleys and automation of the mills, the first transatlantic steamship, and the construction of railways celebrated a mechanistic perspective of nature, so it was natural that scientists visualised light waves too as a mechanical process involving an intangible ether through which the light propagates – after all, mechanical things need something to mechanise the motion. Following James Clark Maxwell’s theory of electromagnetism in 1865, however, and Heinrich Hertz’s confirmation of its prediction of radio waves, even die-hard mechanists agreed this couldn’t be correct: Maxwell’s theory implies that light is the result of oscillating electric and magnetic fields in empty space, which can transmit heat energy without need of intervening particles.
A book from that era proudly promised to explain the new wisdom.4 Comprising 1,258 questions, all answered in 274 pages, it began with ‘What is light?’, ‘What is heat?’, and ‘What are the attributes of heat?’ Then came question number four, which highlighted the enigma at the very foundation of the new electromagnetic revolution: ‘What is electricity?’
Its answer: ‘Electricity is a property of force which resides in all matter, and which constantly seeks to establish an equilibrium. What electricity really is has not yet been discovered.’ In the final quarter of the nineteenth century, scientists sought the answer.
Not only does electricity flow along metal wires like a fluid, flashes of lightning show that it can also pass through the air. This inspired the idea that the flow of electric current might be revealed ‘out in the open’, away from the leads that usually hide it. Electricity can also pass through a liquid containing ions – what today we recognise as atoms that have gained or lost some amount of electric charge.5 When a current passes through acidified water, oxygen forms at the positive terminal – the anode – and hydrogen at the negative cathode. Known as electrolysis, this phenomenon always produces the same amount of hydrogen gas for a given amount of electric charge that has flowed. The hydrogen atoms become positively charged – ionised – and, as opposite charges attract, are drawn to the negative cathode. It appears that each hydrogen ion carries a fixed tiny amount of positive electric charge.
So much for electricity passing through liquids; would it be possible given the technology of the late nineteenth century to investigate electric currents passing through a gas? One product of the First Industrial Revolution was the vacuum pump, capable of reducing gas pressure inside a tube to less than one thousandth of an atmosphere. When a high electric voltage was applied to two metal electrodes inside the vacuum tube, the rarefied gas conducted electricity and produced its first surprise: eerie coloured glows that shimmered like moonlight within the airless container.
UNEARTHLY VISIONS
A pioneer of this work was the British scientist William Crookes. The ghostly glistening is unearthly even when you know what it is, and to Victorian scientists, working in the dark in all senses of the phrase, it could be unnerving. Crookes had become involved with spiritualism following the death of his brother. Seeking scientific proof of the soul, he became obsessed with the subtle lights in his tubes. Convinced that
during seances he had seen ‘luminous green clouds’ and that the lights in his vacuum tube were the same as these phantoms, he announced in 1874 that he had produced ectoplasm.6
Although this led to some ridicule, his research revealed the dramatic way that the lights changed as the pressure dropped. At the lowest pressures then possible, the gas discharge broke up into striations – luminous regions separated by blackness – until eventually at very low pressure the gap expanded, making the whole tube between the negative and positive plates a dark space. Yet curiously it still conducted electricity.
Crookes noticed that the glass at the far end of the tube glowed brightly. Clearly, invisible rays must have travelled through the full length of the dark tube, from its negatively charged cathode, and hit the glass at the far end. To check if this was true, he put fluorescent materials in the path of these cathode rays, which lit up when the rays hit and enabled their paths to be ‘seen’. The final proof of the rays’ reality was that when he placed a piece of metal in the tube, its shadow appeared in the glow at the far end. As to what the rays consisted of, however, no one knew.
In Germany, at the University of Wurzburg, fifty-year-old Wilhelm Röntgen hoped to find out. During November 1895 he was doing similar experiments when by chance he saw an apparition so awful that he wondered if he had taken leave of his senses. By being well prepared, and noticing the unusual, this piece of fortune led him to one of the great breakthroughs in science.
It was approaching midnight on 8 November. Earlier that day, as the wintry dusk was darkening the laboratory, Röntgen had noticed that whenever he made sparks in the tube, a fluorescent screen at the far end of the laboratory appeared to glow slightly. This proved that invisible rays were indeed being produced in the tube and were passing through the glass, crossing the room, and striking the screen, which produced the faint glimmer. After a late meal Röntgen returned to the laboratory. It was now night, but Röntgen closed the curtains to maintain warmth and to ensure the darkness was total. In the blackness the tantalising glow was easier to see. That was when he had a surprise. He had been tracking the cathode rays by putting pieces of card in their way and noting their shadows, but the remote screen continued
to glow whether the cards were there or not as if the rays were able to pass clean through them. He tried to block them with metal, but thin pieces of copper and aluminium were as transparent as the card had been. Somehow Röntgen’s electrical device was producing some novel variety of rays able to pass through objects opaque to light. Whatever these were they could not be cathode rays, which as Crookes had already found and Röntgen confirmed cast shadows of any intervening material. At last Röntgen found something to stop them: a small sheet of lead left a shadow, proving that the mystery rays were real.
He moved the piece of lead near to the fluorescent screen and watched its shadow become sharper. Then he dropped it in surprise: on the screen he had seen the silhouette of the metal apparently held by the hand of a dead man. Astonished, he looked at the dark skeletal pattern of the bones of his hand. Doubting what he saw, he took some photographic film for a permanent record. Röntgen had made one of the most momentous discoveries in the history of science, Xrays, and had seen for the first time images that are today common in every hospital.
Six weeks later, on the Sunday before Christmas, he invited his wife Bertha into the laboratory and took a shadow graph of the bones of her hand with her wedding ring clearly visible. This became one of the most famous images in photographic history. Within two weeks it had made him an international celebrity. The medical implications were immediately realised, and the first images of fractured bones were being made by January 1896.
FEBRUARY FOG
The X symbolised that no one knew what these rays were, and Röntgen appears to have shown little interest in finding out. But on 20 January 1896 Henri Becquerel, a forty-four-year-old Parisian scientist with a strong record of research into phosphorescence, uranium compounds, and photography, learned of Röntgen’s X-rays at a meeting of the French Académie des Sciences. Two doctors showed a picture of the bones of a human hand, which aroused immense excitement, and a copy of Röntgen’s paper on the subject was read.7 Almost
immediately, Becquerel wondered if the rays might be related to the natural phenomenon of phosphorescence where some minerals glow in the dark after first being exposed to light. The question at hand was whether phosphorescent light is entirely stopped by opaque objects or consists of invisible penetrating rays like X-rays?
At the Académie’s next meeting, on 24 February, only five weeks after having first learned of X-rays, Becquerel reported on his first experiments. He told the assembled academicians how, in his first trials, he had exposed some phosphorescent crystals of uranium salts to sunlight for several hours so that they were energised. After wrapping plates of photographic emulsion in opaque paper and placing the crystals on top, he put them next to one another in a dark drawer. Between the crystals and the photographic plate, he placed an aluminium medallion stamped with the head of a figure in relief. When he developed the plates, he found they had indeed been exposed and, most importantly, contained silhouettes of the medallion. The area under the thinner portions of the medal were darker than under the thicker, which caused the head to be clearly visible in the photograph (See inset image 2).
He had proved without a doubt that the crystals were responsible. He also remarked that uranium compounds were particularly good for this. But he was wrong to believe that it was exposure of the uranium to sunlight that provided the energy setting the process in motion. The true secret – that uranium radiates energy spontaneously without need of prior stimulation – was still to be revealed. Like a latter-day Columbus, Becquerel had set off with a wrong hypothesis, which but for serendipity might have been the end of the story.
Seeking further confirmation of what he had found, he planned to continue his experiments, but the end of February in Paris was overcast. Wrongly thinking he couldn’t do the experiment without strong sunlight, he put the uranium crystals, photographic plates, and a copper Maltese cross in a drawer and waited for better weather. A succession of grey days left him frustrated and on 1 March he decided to develop the plates anyway. Expecting to see only a weak image at best, Becquerel was astonished once again to find remarkably clear shapes on the film: the outline of the copper surrounded by a foggy smudge (See inset image 3). During the following weeks he conducted
further tests to confirm that sunlight was indeed unnecessary, but he was obviously already certain. He told the Académie the very next day, 2 March, of his new discovery: activation of uranium compounds can take place in the dark! Becquerel had stumbled upon the phenomenon known as radioactivity – the spontaneous emission of energy by the nuclei of atoms.
Although Röntgen’s discovery of X-rays on 8 November 1895 is traditionally regarded as heralding the nuclear revolution, we now know X-rays are beams of very high energy light produced in the periphery of atoms, their only link to the atomic nucleus being that they stimulated Becquerel to take the next step. And, as we now also know, Becquerel moved things forwards for the wrong reasons while fortunately using uranium in the dank days of February.
Becquerel had discovered the first evidence for the release of nuclear energy, but whereas today this is recognised as seminal, it is ironic that at the time it made no special impact. Radiations were the novelty of the decade: cathode rays, X-rays, radio waves, along with light emitted as phosphorescence or even from living creatures such as fireflies were all vying for attention, and Becquerel’s rays were originally regarded as merely one more for the list. The real birth of the radioactive era was when the Curies discovered the phenomenon in other elements, in particular radium – so powerful that it glows in the dark. It was Marie Curie who invented the term radioactivity and it’s with the Curies that the story of radioactivity and its full implications really begins.
FROM POLAND TO POLONIUM
Marie Skłodowska was born in Warsaw in 1867, the fifth and youngest child of poor schoolteachers. Her father, who taught science and mathematics, valued a love of learning more than anything else in the world. He used every opportunity to interest his children in natural phenomena, such as at sunset taking a few minutes to explain the Earth’s rotation. Whatever was going on, he would always impart his own knowledge about scientific matters to them.
Marie was the brightest of the five, always the top of her class at school. Women were not allowed at the university in Warsaw, so her
father encouraged Marie and her sister Bronya to join with a circle of friends attending the so-called Floating University. The university’s faculty and students met secretly by night at different locations to evade the Russian ruling authorities. Education under such circumstances was all but impossible, so in 1891 Marie left Poland, almost penniless, and moved to a more enlightened France. She enrolled at the Sorbonne to study physics and maths, and it was here that she met physicist Pierre Curie, eight years her senior and already on the faculty of the École de Physique et de Chemie Industrielle.
Marie and Pierre married in 1894. Their daughter Irène, a future Nobel laureate, was born in September 1897, following which Marie began her PhD project. Pierre suggested that she investigate the new Becquerel radiation.
Pierre was an expert on piezoelectricity, the ability of asymmetric crystals to become electrically polarised when subject to pressure. He suggested that Marie use a piece of piezoelectric quartz to make precise measurements of the pressure exerted by the radiation. This proved key, as she was able to quantify its intensity much more accurately than Becquerel had done. She discovered that the radiation’s strength was proportional to the amount of uranium in whatever compound she was using.
Becquerel had suspected the radiation was linked to uranium; Marie had now confirmed it. Whereas Becquerel had concentrated on uranium in the hope of learning more about the radiation, Marie took off in a different direction. Her goal: to see if any other elements showed the phenomenon. She soon found that thorium – a silvery white metal found in granite, where it is more abundant than uranium – also does. This proved the mystery radiation to be a more general natural phenomenon, not a mere curiosity of uranium.
This was the moment when she made her inspired leap. Instead of continuing to examine individual elements, she turned her attention to natural ores. She confirmed that minerals containing uranium and thorium are radioactive, as of course they should be, but to her surprise noticed that the radioactive intensity of some minerals was much greater than could be accounted for solely by their uranium and thorium contents. Most noticeably pitchblende – a brownish-black
rock that is largely uranium dioxide – turned out to be very radioactive when dug from the ground. Marie’s careful measurements soon convinced her that its radioactivity exceeded that from uranium alone and that pitchblende must contain some additional impurity that is highly radioactive.
The challenge now was to extract this mystery ingredient. The only thing known about it was that it must be radioactive. This led the Curies to work together, developing a totally new science known as radiochemistry – the chemical study of radioactivity. Their strategy was to take the ore, dissolve it if possible, and separate its components by standard chemical analysis, and then see where the radioactivity ended up. By repeatedly selecting the highly radioactive extract, the concentration of whatever was causing the radiation was increased. Marie and Pierre found the culprit remarkably quickly. They began the search at the end of 1897; by April 1898 Marie had isolated the source of the radioactivity and by July had determined it to be a previously unknown element. In honour of her birthplace, she named it polonium.
The discovery of polonium was just the beginning, as soon came a more dramatic revelation. Marie continued the purification process and by September the Curies found a further hitherto unknown element whose radioactivity is so powerful that in pure form it glows in the dark and it is warm to the touch: radium.
Today the rays from radium are best known as a treatment for cancer, but when undirected they can cause great damage and suffering. Pierre was killed in a tragic accident in 1906 at the age of forty-six, but his finger joints were already exhibiting swelling caused by radiation, while Marie began to suffer from strange illnesses. Though she survived to the age of sixty-seven, her hands were wrapped to protect the blistering and she eventually died of aplastic anaemia, a condition produced by overexposure to radiation. Her experimental notebooks and even her cookery books were still radioactive fifty years later.
The Curies shared the 1903 Nobel Prize with Becquerel. It was he who had discovered the phenomenon, but it was the Curies who realised its awesome potential. Today, Curie is the name for the scientific unit that quantifies radioactivity’s intensity.
WHAT IS ELECTRICITY?
In December 1884, just four days after his twenty-eighth birthday, Joseph John (‘J. J.’) Thomson was appointed the head of the Cavendish physics laboratory at the University of Cambridge. As an undergraduate he had been a star mathematician narrowly beaten into second place in the University’s highly prestigious mathematical degree. As a result of this perceived ‘failure’ he decided to diversify into both experimental and mathematical issues in electromagnetic theory.
The appointment was remarkable as well as prescient. The first choice had been Lord Kelvin, after whom the scale of temperature is today named. Universally acknowledged as the leading experimentalist of the nation and as a father of thermodynamics in the mid-nineteenth century who had brought scientific analysis to the First Industrial Revolution, Kelvin preferred to stay in Glasgow. Thomson was a surprising alternative, though it is hard to imagine Kelvin could have achieved greater things than Thomson during his subsequent thirty-five years at the helm. In 1897 Thomson would complete the fundamental understanding underpinning the Second Industrial Revolution when he answered the question: what is electricity?
As cathode rays deposit electric charge where they hit a surface, such as the glass of a vacuum tube, Thomson reasoned they must consist of charged particles, which meant they could be deflected by powerful electric or magnetic fields. When he inserted two metal plates into a tube, one charged positive and the other negative, Thomson discovered that cathode rays were repelled by the negative electric plates and attracted by the positive ones. Like charges repel and unlike attract is the rule, from which he proved conclusively the constituents of cathode rays are negatively charged. Thomson’s advantage was in having access to superb vacuum pumps and to more intense electric fields than others at that time. The low pressures achieved with these pumps enabled the charged particles to flow more easily, while the strong electric fields deflected the beams more.
Thomson’s key breakthrough was to use both electric and magnetic fields to move the beam of cathode rays around. Upon hitting the
glass at the end of the tube, the beam made a small green spot. By surrounding the tube with coils of wire, he created a magnetic field which deflected the beam but in a different way to an electric field. Electrostatic forces deal with electric charges while magnetic forces are concerned with moving electricity; by comparing the effect of both you can calculate the velocity and mass per unit electric charge of whatever is moving. By this means Thomson deduced the properties of the cathode rays’ constituents.
He performed a series of experiments using a variety of gases in the tube, different metals in the cathode, and a range of velocities for the cathode rays. Each and every time he found that this ratio – the mass per unit charge – was the same within a factor of about two and, moreover, a thousand or more times larger than anything that had been previously measured in the case of atomic ions. This convinced him that his result was a property of the rays and independent of the gas or cathode materials. If the charged particles were the same as what was responsible for giving charge to ionised atoms, then their masses must be at least one thousand times smaller than any known atom. And atoms were, supposedly, the smallest things of all.
Thomson now made his seminal leap, describing cathode rays as ‘matter in a new state . . . from which all the chemical elements are built up’.8 He named the charged particles electrons. The enormous magnitude of the charge-to-mass ratio is because the mass of an electron is but a trifling part of that of an atom – about one part in two thousand in the lightest atom, hydrogen, for example. The electron is a fundamental constituent building block of the atom. When liberated from within atoms, by heat or other forms of energy, the flow of electrons is what constitutes electric current.
Thomson won the Nobel Prize for his work on the conduction of electricity through gases, in 1906. While rightly famed for his discovery of the electron, the first direct evidence of a subatomic world, his greatest legacy was in the inspired guidance he gave as head of the Cavendish Laboratory to a young student from New Zealand. The Cavendish, having in Lord Kelvin missed the father of thermodynamics and appointed in Thomson the scientist who completed the electrical revolution, now welcomed the architect of the nuclear age: Ernest Rutherford.
From New Zealand to the World
In 1895, the winner of a British Commonwealth Scholarship to Cambridge University declined the award in order to get married. The runner up, twenty-four-year-old Ernest Rutherford, was tending the potato patch on his parents’ farm in New Zealand when news reached him that he had won the prize by default. He threw down his spade and famously said: ‘That’s the last potato I’ll ever dig’.1 Forty-three years later, when he died in 1938, the rustic Kiwi was Lord Rutherford of Nelson, Order of Merit, and a Nobel laureate. His ashes are interred in Westminster Abbey near the remains of Isaac Newton.
A scientific titan who ‘seemed to know the answer before the experiment was made’, even Rutherford’s secondary achievements would have brought fame to other talented scientists.2 Among these accomplishments, he was the first to date the age of the Earth, he was ahead of Guglielmo Marconi in long-range radio wave transmission and briefly the world record holder, he invented methods for detecting ionising radiation, and he predicted the existence of the neutron. Yet these are not what immortalised him. As Darwin is synonymous with evolution, Newton with mechanics, and Einstein with relativity, so is Rutherford with the atom. Faraday and electricity spawned the Second Industrial Revolution; Rutherford was father to the Third.3
Yet Rutherford was an ordinary boy, the fourth of twelve children. On the family farm his father was a skilled mechanic, an expertise which Ernest inherited in his uncanny ability to devise sensitive apparatus seemingly from whatever came to hand; his mother was a teacher dedicated to hard work, an attribute that marked him throughout his life. Rutherford’s birth certificate from Waimea South erroneously recorded his name as ‘Earnest’ – but presciently, for he was gifted