by Kit Chapman
It is only the first example of how elements created in a lab were to change our world.
Notes
1 Fat Man was the code name for the plutonium bomb’s design, which was bulbous because it needed to implode inward to work – something a uranium bomb didn’t have to worry about.
2 All bananas are slightly radioactive, although the lethal ‘banana equivalent dose’ is eating about 35 million bananas at once. If you did that, you’d have bigger problems.
PART ONE
Children of the Atom
CHAPTER ONE
Modern Alchemy
There’s a temptation to think that creating a new element is alchemy. For hundreds of years, men and women had tried to become a new King Midas. Their dream was to turn lead into gold through ‘transmutation’, usually through occult rituals and strange experiments. Some were wannabe wizards who bought into the idea of flowing robes and astrological charts. Others were capable scientists who used coded messages to hide their processes as spell books (mystical fluff such as ‘take our Fiery Dragon that hides the Magical Steel in its belly’ just meant ‘use iron’). All of them lived in a world where ‘elements’ still meant the Greek idea of earth, air, fire and water.
Then, in 1787, Antoine Lavoisier took a major step forward in modern chemistry.1 Four elements weren’t enough for him. Thanks to his wife, Marie-Anne, who had a knack for translating science books, he knew about the basic materials that weave our universe together. He also knew they couldn’t be changed into each other with some magic words. The alchemists were wrong.
Lavoisier set about putting together a list of these ‘chemical elements’. A few mistakes crept in (light and calories made his cut) but it was a good start. For the next 82 years, scientists cleaned up, expanded and arranged Lavoisier’s ideas. In 1869 a Russian chemist, Dmitri Mendeleev, ordered them into what we call the periodic table.
This was an astonishing feat – the equivalent of putting together a globe-spanning jigsaw puzzle without knowing the picture, the shape or how many pieces came in the box. As best as anyone could tell, the elements started at hydrogen and worked their way up to the heaviest yet discovered, uranium. Mendeleev ordered his elements by weight and placed them into groups, arranged in columns with similar properties. If the next known element didn’t fit his pattern, he left a gap. Gradually, as Mendeleev was proved right and missing elements were discovered, the gaps began to fill. An element’s number was arbitrary – just a handy way to keep them in the right sequence.
By the start of the twentieth century scientists knew about the atom. If the elements are the materials of existence, atoms are their tiny building blocks, roughly a billion times smaller than the palm of your hand. Something inside the atom decided which element it made. Thanks to the work of pioneers such as Henri Becquerel and Marie and Pierre Curie, they also knew about radiation. This was the glowing danger, a mystery force of energy emitted from the atom itself. In 1901, at McGill University in Canada, two scientists, Ernest Rutherford and Frederick Soddy, had been playing with the strange phenomenon when they noticed something odd. On the lab bench there had been a small sample of the element thorium. Somehow it had turned into radium.
‘My God, Rutherford!’ Soddy exclaimed, the Englishman losing his usual cool. ‘This is transmutation!’
Rutherford, a pugnacious New Zealander, had hissed him quiet with a withering Kiwi put-down. ‘For Christ’s sake, Soddy, don’t call it transmutation. They’ll have our heads off as alchemists.’
This wasn’t alchemy – it was the birth of a new science. In 1911, Rutherford discovered the nucleus. This was the tiny core at the centre of an atom; as Ernest Lawrence would later say, if an atom was the size of a cathedral, the nucleus was a fly. Lawrence didn’t mention that it would have to be an insanely dense mutant fly that made up 99 per cent of the cathedral’s mass.
By 1913 a new model of the atomic world, put forward by Rutherford and the Danish physicist Niels Bohr, began to explain what was happening. Around the nucleus was a series of imagined concentric shells (see Figure 1), each of which could contain a certain number of small, negatively charged particles called electrons.2 These interact with other electrons in nearby atoms – the basis for what we now know as chemical bonding – to form molecules. Each element has one more electron than the previous, and is eagerly trying to complete its outer shell.
Figure 1 Bohr model of a carbon atom (not to scale), showing a nucleus with six protons and six neutrons, with electrons in two shells.
But the number of electrons doesn’t decide the nature of an element. The same year, a young researcher at the University of Oxford, Henry Moseley, added a crucial piece to the puzzle. Using X-rays, he showed that each element had one unit of nuclear charge greater than its predecessor – that something in the nucleus was providing a positive charge that countered the extra electron. Tragically, Moseley never found out how important his work would be; when the First World War broke out, he volunteered for combat and was killed at the Battle of Gallipoli. But he had made the breakthrough that explained Mendeleev’s elemental order. And five years later, Rutherford had the answer to the mystery of the nucleus.
A nucleus is made up of two main particles. Protons, first found by Rutherford in 1919, decide the element an atom forms. An atom with one proton is hydrogen; two, helium; and so on, up to 92 for uranium. These particles are positively charged, so they constantly try to repel each other: a bit like clenching magnets with the same poles facing each other in your fist. But that still didn’t make sense. How come the nucleus didn’t just rip itself apart? Rutherford realised there had to be something else inside helping to keep the atom together. He imagined a particle of similar size to a proton, but this time without any charge at all, acting as a kind of packing filler. He called it the neutron.
In 1932 the neutron was finally found. By then, Rutherford had moved to run the Cavendish Laboratory at the University of Cambridge, UK, where his deputy was James Chadwick. Tall and thin, with a raven’s-beak nose and stiff manner, Chadwick worked for 10 days straight to find the elusive particle, sleeping only three hours a night. When he finished telling his colleagues all about the discovery, he simply stopped mid-flow and announced that he wanted ‘to be chloroformed and put to bed for a fortnight’. Chadwick had twin five-year-old daughters, so probably didn’t get his wish. ‘It was a strenuous time,’ he later remarked, stiff upper lip intact.
With the neutron, the atomic picture and the periodic table jigsaw made sense. The number of protons, also known as the atomic number, determines the element. The more protons an element has, the greater its positive charge, the more electrons it will have (and, with each row of the periodic table, more shells). The number of neutrons in the nucleus creates different versions of the element, called isotopes. If an atom has six protons, it is always carbon. But you can have carbon-12 (six protons, six neutrons), carbon-13 (seven neutrons) or even carbon-22 (16 neutrons). However, the whole thing is a sort of nuclear juggling act. For light elements, the ideal balance is one neutron per proton. As the elements become heavier and their atomic number increases, more neutrons are needed to keep the atom together. But even then, it’s usually not enough to make things stable for long. When a nucleus becomes unstable, some of these particles are ejected or can change, which is known as radiation.
Today, we have discovered more than 3,300 different combinations of protons and neutrons (in various energy states) – usually referred to by researchers as nuclides. The majority are radioactive and unstable. Even so, we’ve barely scratched the surface of what we believe exists. But for the early pioneers such as Rutherford and Chadwick, the idea that so many different combinations of nuclides could exist was unimaginable.
Until, that is, a ragtag group of impoverished Italian scientists decided to shake things up a little.
* * *
May 1934. Enrico Fermi rushed down the corridor of his lab, racing his student Edoardo Amaldi. Their grey, dirtied lab
coats flowed behind them, the floorboards creaking under the strain and the racket of desperate footfalls disturbing the quiet of Fermi’s mentor’s flat on the floor above. Fermi prided himself on being the fastest physicist in Rome. He needed to be. At the end of the corridor was an experiment where they were trying to create a new element. They had to move fast before their work degraded into something else.
Fermi was the star scientist of Benito Mussolini’s Fascist Italy. Short and dark, his face dominated by a cheery grin under a long, thin nose and a large, semicircular forehead, Fermi certainly made an impression. His mind raced, quickly coming up with rough answers to questions that seemed impossible.3 When he’d made professor aged just 24, Fermi had set up a lab in the University of Rome’s physics department in an old villa off the Via Panisperna in the centre of the city, and had sworn he would drag Italian science kicking and screaming into the twentieth century. He had soon attracted a team of young, fresh talent who didn’t mind breaking, bending or ignoring the supposed laws of the universe. None of them, including Fermi, had any real experience in experimental nuclear physics. None of them cared. To them, Fermi was simply ‘The Pope’, and if he said something could be done, they’d do it. Fermi’s ‘Via Panisperna Boys’ were atomic physics’ answer to the Sex Pistols: punk scientists who were about to make their own rules.
Despite Mussolini’s patronage, the boys were broke. While their British, French and American rivals could afford the best equipment, Fermi’s team had to improvise. Geiger counters were made at home through trial and error. Teenage brothers were bribed to help when something heavy needed lifting. Lacking any protective equipment, the team would hide at the end of the corridor to shield themselves from certain death when dealing with radiation – leading to Fermi’s frantic footrace to get his results.
A few decades earlier, Ernest Rutherford had discovered three distinct types of radiation, the first two of which he called alpha and beta. Alpha radiation saw the nucleus emit an alpha particle (two protons, two neutrons – the equivalent of a helium nucleus). This is how Rutherford and Soddy’s thorium sample (element 90) had turned into radium (element 88): by losing two protons, it had dropped two places back on the periodic table. The time it took for half of a sample to degrade through radioactivity was known as the half-life.
Fermi was interested in beta radiation. This didn’t cause the loss of any protons at all, but turned a neutron into a proton, moving the element one place further along the periodic table, and spitting out an electron in the process (the loss of the electron creating the radiation in question).4 But the equation didn’t balance out – not enough energy was being lost. Fermi suggested that something even smaller than the electron was being thrown out of the atom too. Sadly, the journal Nature didn’t believe him: the paper was rejected for ‘speculations too remote from reality to be of interest to the reader’. Infuriated, Fermi decided to do a few silly experiments, just fun in the lab, to take his mind off things. What better way to forget your troubles than to make some stuff glow in the dark? Firing off his thoughts about beta radiation to a few other journals, he decided to move on and do some practical research instead – and a new idea called artificially induced radiation caught his eye.
Bombarding an element with alpha particles resulted in an element gaining two protons and two neutrons. In France, Irène Joliot-Curie and her husband Frédéric had turned aluminium (element 13) into phosphorus (element 15) by doing just this; Irène was the daughter of the legendary Marie and Pierre Curie, and radioactivity was the family business. Alpha particles, thanks to their protons, were positively charged, just like the nucleus. This created two problems: first, the negatively charged electrons orbiting around the nucleus would slow them down; second, and worse, they had to be smashed into the target at high speeds to get past the electrostatic repulsion of the nucleus itself – again, just like pushing two similarly charged magnet poles together. To gain entry through this invisible force field, known as the Coulomb barrier, you needed a staggering amount of energy. That required a particle accelerator.
Fermi didn’t have one. He couldn’t afford one. He had nowhere to put one. Instead, he had a brilliant idea. Why not just bombard your target sample with neutrons instead of alpha particles? They didn’t have any charge, so couldn’t be repelled; if a neutron hit the nucleus, it was just going to slip into its heart, raise its energy and cause radioactive decay. Perhaps something interesting would happen.
The Via Panisperna Boys had set to work. The first problem was getting hold of neutrons. In the basement of the building, another professor kept a sample of radium in his safe – a single gram, worth almost 20 times the Boys’ annual budget. Radium was known to decay (through alpha radiation) into a gas: radon. Unable to steal the sample, Fermi arranged a system of pipes to pump the gas from the safe into small vials, where it was mixed with beryllium powder. Highly radioactive, the radon gas gave off yet more alpha particles; these struck the beryllium atoms, causing them to emit neutrons. Fermi had created a home-made neutron beam. He just needed something to fire it at. Why not fire it at everything?
Fermi wrote out a shopping list covering every element or compound that could be used as a target and gave it to one of his subordinates, Emilio Segrè (Fermi, according to his wife Laura, ‘disliked shopping intensely’). He then skipped off home for lunch and a nap, while Segrè set off around Rome trying to track down ‘The Pope’s’ extensive demands.
Segrè was a cornerstone of Fermi’s schemes. The son of a paper magnate, he had initially trained as an engineer and spent two years in the Italian army working on anti-aircraft guns before switching to physics. Following Fermi’s instructions, he soon cornered a supplier, but the man only spoke a regional dialect and, having been raised by priests, Latin; fortunately, Segrè knew enough of the dead language to make himself understood. The chemical shopping list was soon filled; the supplier even gave away some unused stock, high on dusty shelves, for free. Nobody had asked for those elements in 15 years.
The team tried their targets in order of their atomic number. The first few elements didn’t really do anything. The next gave off alpha particles, moving them two places back on the table. But the heavier elements didn’t give off alpha particles so easily. Instead, the force that kept the nucleus bound together – the nuclear strong force – held onto the neutron. This caused the element to eventually undergo beta decay, creating an element one place further along the periodic table. Fermi had stumbled on a process called neutron capture.
Back to Fermi’s frantic sprint down the corridor. After weeks of study, the team had finally reached the end of the periodic table. They were about to see what happened to the heaviest element: number 92, uranium. Rounding the door ahead of Amaldi, Fermi slipped in first to grab the samples and check the results. Quickly, the Boys worked to analyse what they had found. The uranium had transmuted into something else. The only question was which way it had gone: alpha decay into a known element, or beta decay into something new?
The team compared the new substance’s half-life and chemistry against the known elements as far back as lead (element 82).5 If alpha decay had occurred, it would have started a ‘decay chain’ – turning into element 90, then 88, then 86 and so on. But there was no sign their creation had undergone alpha decay at all. The only explanation the team could think of was that the sample had undergone beta decay. Further tests by the Boys soon found a second mystery element. Again, the only explanation was another beta decay.
Up until that moment, most physicists didn’t believe there could be an element heavier than uranium. It was the end of the periodic table. It had been known about since its discovery in 1789, while Lavoisier was still alive and before the periodic table even existed. Fermi and his chaotic squad of rebels, using home-made gadgets and dusty targets given away for free, had done something the greatest laboratories in the world, using the greatest machines of the day, hadn’t even thought possible. They had just broken the boundaries of Dmitr
i Mendeleev’s table of elements.
Fermi told the world he had created elements 93 and 94.
* * *
It’s 2018, some 78 years after Fermi’s announcement, and I’m stood in the heart of Rome. If I’m going to understand why the elements matter, I need to step back to the first attempts to push beyond uranium. And that means trying to find a trace of Enrico Fermi.
The Eternal City doesn’t change. Rome is still as Fermi would have known it, a hilly maze of effortless disorder somehow manicured into one of the world’s greatest capitals. It is a hive of accented shouts from restaurants, apartments and taxis; of crumbling buildings coated in graffiti and licked with flyers; of tight alleyways that suddenly twist you into sweeping, open avenues lined with marble columns built to honour long-dead emperors. No other city can pull off disrepair quite like Rome. No other city can exude such lazy, sun-drenched style. No other city could have produced Fermi.
It’s a long journey from New Mexico, and a strange transfer from barren wilderness to the kinetic pleasures of a European capital. The Via Panisperna still exists, winding down from the towering Basilica of Santa Maria Maggiore, its route cutting a bumpy tumble over the Esquiline and Viminal hills toward the city’s ancient heart. Part of the trendy, artisan quarter, the road’s cobbled surface has been beaten flat by Fiats and Vespas, and its buildings house fashionable hair salons, quiet bistros and high-end art galleries. A short walk away, visible from the end of the street, the Colosseum rises up in the distance. I stop and catch my breath, admiring the colonnades of the ancient gladiatorial fighting pit as they are rendered by the setting Latin sun.