by Kit Chapman
With fission, the material doesn’t stay in one place: like a miniature nuclear bomb, the atom blows itself apart, scattering itself in all directions.1 Following the revelation that fission occurred, McMillan decided to run some experiments to see just how far things pinged away. Heading to the nearest atom smasher, he started pummelling a sample of uranium trioxide. Soon, he got a very strange reading. Something had been left near his original target material. It wasn’t uranium, and it hadn’t flown off far enough to be a fission product. Weirder still, the unknown radioactive lump had a half-life of 2.3 days, which didn’t match anything previously recorded. Was it the real element 93?
McMillan was flummoxed, so he asked Segrè – comfortably settled in California – to investigate. The Italian was a bad choice for a lab partner. Following the columns down the periodic table, element 93 was supposed to behave like the elements in group 7. Instead, it behaved like a group called the rare earth metals, or lanthanides – a line of elements beginning at lanthanum that all acted similarly to each other. These elements were so odd they had been considered apart from the rest of the periodic table, isolated on a naughty step just below the main chart (to this day, they are almost always displayed apart from the main table). Failing to learn from the slapdash approach to chemical confirmation during his days under Fermi, the Italian decided it wasn’t anything important and told McMillan to forget about it. He even went as far as to publish a paper: ‘An Unsuccessful Search for Transuranic Elements’.
McMillan wasn’t so sure. If his discovery was a fission product, why hadn’t it been scattered off like everything else? If it was an unknown isotope of uranium, why didn’t it behave like one? The result gnawed at the back of his mind. Over the winter, he tested his mystery sample with hydrofluoric acid and a reducing agent. The result – using chemistry so simple a student could do it – ruled out any of the rare earths. As he worked, life continued. The Second World War broke out in Europe; Gone with the Wind and The Wizard of Oz were released; the campus swung to the beats of Glenn Miller and Billie Holiday. In May 1940 Abelson returned to Berkeley on holiday (he’d since graduated and moved to Washington, DC), and McMillan asked for a second opinion. In two days, Abelson had performed the full chemical work-up Segrè hadn’t.
The results were conclusive. Edwin McMillan and Phil Abelson had discovered the real element 93. The duo published their findings in the Physical Review. The Second World War meant there was no fanfare; the great minds of Britain, France and Germany were at war. The only research into fission seemed to be coming out of Russia, where a pair of young physicists had proved that elements can spontaneously fission in nature. Instead of the physics world eagerly discussing their discovery, they received an official protest from James Chadwick and the British, currently under siege as they prepared for the Battle of Britain: Would you mind awfully just shutting up about things the Nazis might find useful? Abelson headed back east; McMillan kept working.
The person following McMillan’s progress the closest was Seaborg. Both men lived only a few rooms apart, and the chemist pursued the element maker around campus asking questions: in the lunch hall, in the corridor, even into the shower room. Seaborg was hooked, in love with the idea of a new element, desperate to know every detail. McMillan happily took Seaborg into his confidence about his latest scientific escapade. Using a cyclotron, he was bombarding uranium with deuterons (an isotope of hydrogen, with one proton and one neutron) to try and make an even shorter-lived isotope of element 93. His hope was that this more unstable version would undergo beta decay, turning into element 94. Things seemed to be going well. Then one day, McMillan was gone.
Seaborg soon found out why. The US was preparing to join the war, and Lawrence had been asked to give up his best scientists to the military. Along with Alvarez, McMillan had been sent to Boston to work on developing radar detection. Not willing to surrender his new passion, Seaborg wrote to McMillan asking if he could take over the project. Seaborg later recalled in his autobiography: ‘Ed wrote back immediately to say he had no idea when he would return to Berkeley and expected a long absence, so he would be happy for us to continue.’
The chemist wasn’t going to pass up his opportunity.
* * *
A neutron walks into a bar and orders a drink. ‘How much?’ the particle asks. The barman shakes his head. ‘For you, no charge.’
The oldest joke in atomic physics is proudly emblazoned on the menu at the Berkeley chemistry department’s coffee stand. I’m sat just outside, fighting off the jetlag and wind chill with caffeine and carbs. I thought California was supposed to be sunny? There’s a nip in the air this morning and I’m beginning to regret not bringing a thick sweater; part of me wants to give in, dart into one of the town’s countless clothing and thrift stores and get a hooded top – probably a goofy one with ‘I heart San Francisco’ all over it. For now, hot coffee will do.
Berkeley is a small town that morphs seamlessly into bustling Oakland, a relaxed suburb filled with counterculture shops, cheap eats and bars proudly pledging allegiance to its Golden Bears sports programme. The University of California campus dominates the whole area, its manicured lawns and imposing halls resting on a rise that slowly steepens, building to a climax at Grizzly Peak. Originally named after an Irish bishop who didn’t believe in the material world, Berkeley has always been home to the raucous and the radical – Ginsberg to Green Day – its left leanings evident on every lamppost or window plastered with slogans such as ‘Occupy’ and ‘Resist’. In the 1960s the Bay Area was the epicentre of the ‘flower power’ movement and anti-Vietnam protests; today it wears its campaigns for LGBT rights and an end to pseudoscience with righteous pride.
This is one of the world’s great science hubs. Starting with Lawrence’s Rad Lab, Berkeley has been on a roll of Nobel Prizes and ground-breaking science for 80 years. Just strolling through campus, you could bump into George Smoot, one of the world’s leading experts on the Big Bang, or Jennifer Doudna, the biochemist whose CRISPR discovery could allow us to rewrite our genes. The whole complex has a collegiate air, a sense that something very smart is going to happen, mixed with breezy cool and a hint of mischief. Quite what Bishop Berkeley would have made of it is anyone’s guess.
LeConte Hall and the Campanile still stand, though the old Rad Lab has since been torn down. Apparently, someone finally realised that conducting radioactive experiments in the centre of one of the world’s busiest campuses was a bad idea. Today its descendant, Berkeley Lab (officially Lawrence Berkeley National Laboratory), sits atop the sharp rise behind the university grounds, accessible either by a stiff hike or a convenient shuttle bus.
I’m not here for the lab today; that’s a mission for another time. I’m here to break into Gilman Hall. Gilman is another of the beautiful, grey-stone buildings on the campus where Lawrence’s men cut their teeth. In 1940, Seaborg had recruited two collaborators, Joseph Kennedy and Arthur Wahl, to continue McMillan’s hunt. Aware that their discoveries could be used for an atomic bomb, the team had sworn to work in secrecy. To complete the chemical separations required to explore new elements, the team needed space away from prying eyes. The third floor of Gilman was the best they could come up with.
Sneaking in through the large oak doors that guard the hall’s main entrance, it’s easy enough to slip onto the staircase – wonderful, heavy concrete stairs with sturdy metal banisters and wood lacquered to a sheen – and climb up to the top floor. Here are attic rooms, still in use by the chemistry department as offices. In Seaborg’s day they served as miniature lab spaces with industrial sinks and workbenches, with bottles of reagents, hand-blown glass beakers and retorts fighting for space against Bunsen burners, jars of powders and char-blacked draining boards. Cramped and cosy (particularly for the tall Seaborg), it’s the opposite of the vast underground lair Hollywood has associated with scientific breakthroughs. Down a whitewashed corridor, exposed pipes humming overhead, next to an emergency shower for chemical mishaps, you
’ll find a hardy door. On the wall are two plaques that hint at what came to pass in the locked chamber. Room 307. The place where Glenn Seaborg isolated plutonium.
In mid-December, following McMillan’s plan, the trio created the new isotope of element 93. It was a vigorous beta radiation emitter, meaning it was likely turning into yet another element. But they had also made something that fizzed with alpha particles instead. Could 93 have beta decayed and given birth to an atomic daughter?
Work continued through a long, wet winter. Room 307 soon stank with reagents and reactions, forcing the team to open the windows and work out on the balcony. Here, in full view of the world, three men in their twenties played with perhaps the most secret substance ever to have existed. Much of the work was carried out at night, the conspirators making desperate runs with their radioactive samples between the Rad Lab machines and the Gilman lair. All that was missing was the final confirmation that element 94 was real.
The breakthrough came as a cliché. Every scientist knows that, sometimes, the best results come when everyone else has left and you’re trapped alone in the lab. On the night of 21 February 1941,2 a wild storm battered and bruised the San Francisco Bay. Wahl was still in the attic space, the whole room rattling with the wind and rain, lightning flashes occasionally illuminating the downpour outside. A little past midnight, his eyes growing heavy, Wahl finished his last chemical test. Chemists are obsessed with oxidation numbers – how many electrons lost or gained by an atom when it forms a compound. The group had just proved that the radioactive daughter particle had a higher oxidation number than any known element it could have been. It had to be element 94.
Standing in the hall, the place resonating with history, I can’t help but imagine Wahl laughing maniacally as the balcony doors burst open and the thunder pealed behind him. It’s probably the only time in scientific history mad scientist chic would have been appropriate.
* * *
To make a nuclear bomb, you need a chain reaction – one atom going off won’t release enough energy to make a big enough bang. This requires a ‘fissile’ isotope – one that, if hit by a neutron, will send neutrons flying out in turn, like a pool ball hitting the stack. These neutrons will hit other atoms, causing them to explode, which will send more neutrons out, causing yet more explosions, sending yet more neutrons out, etc. If you have enough fissile material – the critical mass – you get a sustained nuclear chain reaction. One atom undergoing fission could flick a speck of dust; 6kg (13lb) of atoms undergoing fission almost simultaneously could level a city.
As far back as late 1939, at the request of Albert Einstein,3 President Roosevelt had already put together an advisory committee to consider the feasibility of an atomic weapon. There was one obvious choice of fissile material to make the bomb: the naturally occurring uranium-235. Most natural uranium is U-238, but this was easy to mine, and could then be enriched by a process called gaseous diffusion to remove some of the unwanted isotopes and increase the concentration of U-235.
The second possibility was Seaborg’s suspected element 94. By the summer of 1941, Seaborg’s team had completed the final hurdles surrounding their creations. Even before Wahl’s final tests, the group became aware that at least one isotope of their creation might be fissile. Here, a familiar face joined the party. After dismissing McMillan’s discovery, Emilio Segrè had been working with a different group and discovered yet another element, the missing 85, later named astatine. Lawrence asked Segrè to partner up with Seaborg to see if element 94 could make a bomb.
Seaborg wasn’t happy. Segrè was a lousy chemist, and as an Italian he was classed as an ‘enemy alien’ and was not allowed to know the details of what was going on. The situation was crazy; Seaborg would gather chemicals and tell Segrè what to do, but could not tell him what substances he was dealing with or why he was using them. But Segrè had contacts Seaborg could only dream about. When the team needed a larger amount of uranium to bombard, Segrè made a call to Enrico Fermi, who had settled on the East Coast. Soon, 5kg (11lb) of uranium arrived at Berkeley with his former mentor’s compliments. With it, the unlikely duo worked out that you’d need to bombard 1.2kg (2.6lb) of uranium in a cyclotron to get 1 microgram (or μg – a millionth of a gram) of element 93, which degraded quickly to 94.
Now with enough element 94 to play with, Seaborg and Segrè soon determined that one of its isotopes was fissile. The team estimated that its fission rate was 1.7 times that of uranium. Element 94 was not just an option for a nuclear bomb. It was the best option.
Lawrence was a member of the advisory committee and sent Seaborg across the US to explain what he had found to Arthur Compton, the committee member tasked with writing the report on whether a bomb was feasible. Compton listened, but decided against telling the president about Seaborg’s new element. On 6 December 1941 the advisory committee met and decided they would proceed with making a nuclear bomb using uranium-235.
After the meeting Compton went to lunch with two of the committee members and brought up the topic of element 94 as an alternative to uranium. He had been talking with Lawrence and other scientists who had convinced him that the Berkeley discovery was worth investigating further. ‘Seaborg tells me,’ he informed his companions, ‘that within six months from the time [94] is formed, he can have it available for use in the bomb.’
One of the diners was James Conant, the president of Harvard University. The New Englander practically sneered at the suggestion. ‘Glenn Seaborg is a very competent young chemist,’ Conant remarked, ‘but he isn’t that good.’ Still, the group agreed it was useful to have an alternative option for a bomb just in case the US found itself at war.
Twenty-four hours later the Japanese attacked Pearl Harbor.
Notes
1 Things don’t stay in one place with alpha or beta decay, either; part of the big challenge in nuclear physics is nothing ends up where you want or expect it to go.
2 The plaque outside 307 insists that the discovery was the night of 23 February. Seaborg always claimed it was during the storm, and that’s good enough for me.
3 The letter was actually written by Leo Szilard, but was signed and sent by Einstein – and if Albert Einstein tells you something is a good idea, you should probably listen.
CHAPTER THREE
How to Build a Nuclear Weapon
In the summer of 1941, while Seaborg was flying across the country trying to sell his new element, he had someone on his mind. For the past year he had regularly bumbled into Ernest Lawrence’s office, always on some flimsy pretext, just to talk to his secretary Helen Griggs. Griggs, still only 24, had captured Seaborg’s heart. An orphan born in a home for unwed mothers in Sioux City, Iowa, her adopted parents had given her a good upbringing and outstanding work ethic. When her father died, she and her mother had moved out west to California, where she’d worked several jobs to put herself first through an associate degree at a local community college, then university. While studying for her degree she’d started working in the Rad Lab’s secretarial pool; when she graduated in 1939, the role became full-time. One of her first tasks was trying to persuade her boss to accept the Nobel Prize: Lawrence was in the middle of a tennis match at the time and, unlike Enrico Fermi the year before, had the luxury to decide that the call from Stockholm could wait.
As Lawrence’s secretary, Griggs already knew about the secrets of the Gilman Hall attic – she was the one typing up the team’s reports. She also knew Seaborg had broken up with his previous girlfriend because he was playing with new elements when he was supposed to be out playing with her. (‘She’d taken that as a sign of my priorities,’ Seaborg sheepishly recalled in his autobiography, ‘which I guess it was.’)
Griggs had a soft spot for the tall, awkward chemist. When Seaborg’s friend Melvin Calvin told her he was picking up Seaborg from the airport, she agreed to tag along in his Oldsmobile convertible. Calvin was aware of Seaborg’s infatuation; he was fed up with his friend’s pining and decided to play Cupi
d. Griggs was more than happy to play along.
The Oldsmobile wasn’t a subtle car; its bonnet was almost as long as the cab itself, with smooth art deco lines that oozed luxury. Landing at Oakland from the sleeper flight, Seaborg spotted Griggs in the passenger seat and his heart leaped. Seaborg took the wheel – he paid Calvin’s insurance for the right to use the car whenever he liked – dropped his friend off at Berkeley and took Griggs for a drive through the golden hills of California’s wine country. Past the peaks that surround the San Francisco Bay, the world opened up to a hot, lazy land of small farming communities as far as Livermore. As they drove, Seaborg talked: finally, he had someone he could open up to about his secret work. His new girlfriend listened enraptured. The couple were made for each other.
When the US entered the Second World War after Pearl Harbor, Griggs was there to support her boyfriend. Arthur Compton took responsibility for the element 94 part of the bomb project, and Seaborg began to feel pressure to deliver the material he had promised. ‘Before, we’d been jogging toward our goal,’ Seaborg recalled, ‘now we hit a dead run.’ In early 1942 Seaborg received his orders. Compton wanted to bring all of his scientists together at the University of Chicago’s newly established Metallurgical Laboratory. Seaborg was moving east.
The evening Seaborg learned about his move to Chicago, he took Griggs for fried chicken at Tiny’s Waffle Shop to ask her to come with him. Forever bashful around her, he promptly lost his nerve. The couple headed back to her apartment, where Seaborg again tried – and failed – to express himself. Finally, he just came out with it: ‘I’m sitting here trying to think of a way to ask you to marry me.’
Griggs said yes.
The news shocked Ernest Lawrence (the romance had been a bigger secret than element 94), but he agreed to let her go. Soon, rumours circulated around the Rad Lab that Seaborg had only proposed because he needed a good secretary. The couple didn’t care. In April 1942, on his thirtieth birthday, Seaborg arrived in Chicago. Two months later he returned for Griggs. They left California, stopped at the first town across the border in Nevada to get a ‘quickie’ marriage, and then headed to their new home.