Superheavy

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by Kit Chapman


  Even so, accidents happened. The chemists had to do these separations behind a wall of lead bricks to avoid a dose of lethal radiation, using a carefully placed mirror to guide their hands. One night a lead brick fell on a beaker, leaving around a quarter of the world’s entire supply of plutonium-239 soaked in the Sunday edition of the Chicago Tribune. Fortunately, a little chemistry went a long way: the team reclaimed all of it by dissolving the newspaper in acid.

  General lab safety was another challenge. Even though plutonium only produces alpha particles (which can be blocked by as little as a sheet of paper), if it enters the body it can end up in bones, creating a permanent source of internal radiation that can slowly and silently kill. One night, a worker using his bare hands gripped a test tube too tightly and it broke in his palm. Seaborg collected about 1mg of plutonium from his colleague’s hands – the weight of a small snowflake. It was enough to force the scientist to wear gloves whenever he ate or drank until the radiation count faded.

  Burnout was a danger too. The scientists worked six days a week, usually all day and into the evening. Seaborg began to have anxiety attacks at night, and the stress and nervous exhaustion finally manifested as a fever that put him in hospital. To fight off his ill mental health, the team leader began to exercise vigorously and was soon addicted to golf, climbing steep hills and running up stairs. The anxiety faded.

  In Chicago, Fermi had demonstrated that a sustained nuclear chain reaction was possible, while Seaborg’s team had shown that plutonium could be separated. At Oak Ridge, the two innovations had been put together. In 1944 the team was ready to scale up production. Thompson, the obvious choice to oversee the chemistry, was sent to Hanford, Washington, 1,550km2 (600 miles2) of plant deep in the isolation of the Pacific Northwest, to oversee the chemical arm of the first full-scale plutonium production line. Synthetic elements were about to be produced on an industrial scale.

  * * *

  Roberto and I have arrived at the control room of the High Flux Isotope Reactor (HFIR) at Oak Ridge. We’re looking out from the gallery window at a pool, a strange blue light coming up from below the water. Deep below the surface, 5m (15ft) down, is the top of a nuclear reactor. The glow is Cherenkov radiation – charged particles passing through water to show that a fuel element is nearly spent. The brighter the blue, the sooner you need to replace your fuel. ‘That one is about a month old,’ says Kevin Smith, former deputy division director for the reactor research division. ‘We’re getting ready to shut it down.’

  He doesn’t mean the whole reactor – HFIR is due to keep going for decades. He just means changing out the core. HFIR’s reactor fuel isn’t fed into slots by three men on a lift but lowered in compact cylinders. The water is everything, cooling the reactor and slowing the neutrons. The whole tank flushes through about 275,000l (60,500 gallons) a minute, shooting through at about 15m (50ft) a second. Instead of graphite, the fuel is surrounded by beryllium – an excellent neutron reflector. ‘So, neutrons will reflect, bounce off and come right back into the core,’ Smith says. ‘This is all a flux trap, neutrons leaking in.’

  This is by design. While most nuclear power plants focus on energy, the aim here is neutron production (even so, HFIR produces 85MW of thermal power, theoretically enough to supply a city of 100,000 people). It’s one of only two facilities in the world focused on making the first couple of elements beyond uranium, although it can go all the way up to element 100. The other, the Research Institute of Atomic Reactors, is in Dimitrovgrad, Russia.

  Plutonium is still as much in demand as it was during the Second World War, although today’s reasons are entirely peaceful. ‘We’re making Pu-238 for NASA,’ Smith says. ‘Anywhere the sun doesn’t shine, you can use it to generate power. If you go to outer space, and you’re far away from the sun, you got nothing else.’

  ‘It’s being used in probes?’

  ‘Yes, Voyager is powered by plutonium,’ Roberto adds. ‘And the Mars Curiosity rover too.’

  It’s far from the only point of pride in the reactor’s output. The products are used to improve the safety and efficiency of solar cells, computer hard drives and advanced medicines. Previous reactors at the lab have even played secret, silent roles in history. In 1963 neutrons from the Oak Ridge Reactor – HFIR’s predecessor – were used to bombard lead fragments from bullets found at a murder scene and gunshot residue from paraffin casts of the suspected murderer’s hands and face. Using the neutrons, scientists were able to determine that the bullets all came from the same weapon – and that Lee Harvey Oswald’s gun had assassinated President John F. Kennedy (the casts directly linking Oswald were inconclusive).

  Standing this close to a nuclear reactor is awesome. The whole thing looks like an industrial movie set – lots of monitors, dials, gauges and unlabelled buttons that glow when you press them. Perhaps the most amazing thing is that the design was just someone’s thesis. Back in the 1950s you couldn’t get a nuclear engineering degree from a university, so a school was set up on site to teach nuclear engineers. Somehow, without the aid of a computer, a student called Dick Cheverton led a team that designed something that nobody’s been able to improve since; now in his nineties, Cheverton is still on Oak Ridge’s books. His reward was a diploma that proclaimed him to be a ‘Doctor of Pile Engineering’. DOPE for short.

  We walk over to a dummy cylinder (the kind loaded into the reactor) that’s propped up inside the control gallery. Half a metre (2ft) long, its interior consists of three rings, like a bullseye. The outer and middle sections are filled with 540 metal plates, curved to provide constant width for the coolant to flow through. From the top, it looks a bit like a jet engine. You stick your target rods in the middle, and all the neutrons get directed back to them. Smith walks over and picks up what looks like a short aluminium javelin – or ‘rabbit’, as the team prefers. ‘You screw off the top and then you can put seven of these target rods in there.’

  He passes the target rod to me. It’s basically just a hollow tube to hold your target pellets. Then it sits in the reactor for a few cycles (about 24 days each) until the pellets turn into something else. The whole thing is ridiculously light, so much so I could balance it on the end of my … crash.

  ‘You’ve broken it,’ Roberto laughs.

  Smith sighs. ‘That’s what always happens. I’ll get an operator to put it back together.’

  ‘I hope it wasn’t expensive,’ I mumble sheepishly.

  Another sigh. ‘These little guys are about $10,000, something like that.’

  Time to leave. Quickly. My next stop is up the hill, where the chemists separate out the reactor’s products using similar techniques to those pioneered by Thompson 70 years earlier. They don’t just produce plutonium. By December 1943, with work in Chicago slowing down, Seaborg’s scientific mind had drifted away from just the Manhattan Project and back toward element hunting. In the two and a half years since its discovery, plutonium production had gone from a few atoms to quantities large enough to use in experiments. What would happen if you put plutonium in a cyclotron and bombarded it? Would another neutron be captured and turned into a proton? Could there be element 95, or even 96? Seaborg formed a small team to find out.

  The answer would end up rearranging the periodic table.

  Notes

  1 This wasn’t the end of code words. During the Manhattan Project, the fissile isotope of plutonium, Pu-239, became known as ‘49’ – the last digits of 94 and 239.

  2 In 2006 astronomers decided Pluto would be reclassified as a ‘dwarf planet’, rendering Seaborg’s stylistic choice pointless.

  3 It’s weird to know I’ve walked inside the world’s fastest computer. The operators find it hard not to make jokes about movies such as WarGames or being able to play games such as Crysis. I did ask what happened if it was accidentally turned off. ‘We turn it back on again,’ came the puzzled reply. ‘It’s just a computer.’

  CHAPTER FOUR

  Superman vs the FBI

 
In April 1945 the New York offices of Detective Comics, Inc. received a visit from the FBI. Polite yet forceful, the agents were taken to meet publisher Harry Donenfeld. It was about the company’s most popular comic strip. The G-men demanded that the latest syndicated story be pulled from publication immediately. Donenfeld called in editor Jack Schiff, who was running the storyline.

  Why, the FBI agents asked Schiff, was Superman leaking state secrets?

  In the latest strip, Science and Superman, the Kryptonian hero had agreed to undergo a few tests in a particle accelerator for a scientist. ‘No, Superman! Wait! Even you can’t do it!’ his lab-coated ally warned, panicked by the idea of someone being hit by ‘electrons travelling at 100 million miles per hour and charged with three million volts’. The equipment – and the numbers – were a little too on the money to be a coincidence. Fortunately, the FBI soon realised no one was a spy: the writer, Alvin Schwartz, had simply copied the idea of an ‘atom smasher’ from something in a 1935 issue of Popular Mechanics.1 The article had described one of Ernest Lawrence’s cyclotrons.

  A particle accelerator is basically a giant gun. Instead of bullets, it fires electrically charged particles down a vacuum tube, which contains a series of electrodes. By flipping the polarity of the electrodes at the right time, researchers can push and pull particles down the tube and make them go faster and faster. It’s a carrot-and-stick approach, using the same idea that makes a TV or X-ray machine work.

  The first particle accelerators were ‘linear accelerators’, which shoot particles in a straight line. The problem is that to get a charged particle up to the kind of speed (and therefore energy) needed to punch through a nucleus’s Coulomb barrier requires an accelerator more than 100 metres long. This is far too large to fit into most labs.

  Enter Lawrence’s invention. A cyclotron fires particles in a spiral, starting in the centre and looping out through two giant semi-circular electrodes called dees (because of their D shape). The whole thing looks like an oversized zinc battery, sandwiched under a giant magnet that helps the particle to bend around the spiral track due to something called the Lorentz force. With every completed loop the particle gains velocity, before it finally whizzes out of the machine.

  Both linear accelerators and cyclotrons have been used to discover elements. Once the ions (atoms stripped of electrons so they have an electric charge) have been accelerated, they are rushed down a ‘beam line’ toward whatever target the researchers are trying to hit. Then all the team can do is sit, wait and hope for the best.

  Thanks to their circular shape, a cyclotron is far more compact than a linear accelerator. Lawrence’s first accelerator, the size of his hand, was made out of copper tubes, wires, a vacuum pump, sealing wax and a kitchen chair: the whole thing cost about $25. By 1932 he had built a device 69cm (27in) in diameter, capable of accelerating particles up to energies of 4.8 million electron volts (MeV). This isn’t much in the scheme of things – a neutron produced by fission has an energy of 2MeV – but it was more than enough on the atomic scale. Lawrence’s breakthrough meant you didn’t need a particle accelerator the length of a football field any more.

  Not everyone was impressed: you still had to hit the nucleus, something unimaginably small. ‘You see,’ Albert Einstein said dismissively in 1934, ‘it is like shooting birds in the dark in a country where there are only a few birds.’ Einstein was right. Yet even in a dark country, you’ll eventually hit something if you keep going for long enough. The nucleus had been hit before – and the cyclotron effectively gave everyone a super machine gun with an infinite supply of bullets. One of the later element creators, Mark Stoyer, explains it to schoolkids by asking them to throw marshmallows at each other’s mouths from the other side of the classroom. Most of the time they miss entirely; sometimes they get an unwanted reaction and the marshmallow bounces off a nose or an ear. But sometimes – rarely – they get lucky and it goes in. ‘Now,’ Stoyer ends, ‘imagine you’re throwing 6 billion bags of marshmallows a second. For three months. And every bag has 1,000 marshmallows in it. Science gets messy sometimes.’

  Lawrence had made larger and larger cyclotrons. By the time the invention won him the Nobel Prize (disturbing his tennis match and annoying his secretary in the process), his latest cyclotron was 150cm (60in) wide, its magnet large enough that the whole Berkeley Rad Lab – 46 people – took a group photo of them sitting on top of it. There were other cyclotrons scattered around the world too: James Chadwick had built one in Liverpool, and the Germans and Russians both had one, as did the Japanese. It was hardly a state secret.

  Figure 4 Ernest Lawrence (bottom row, fourth from left) and his team sitting on the magnet of the 60-inch cyclotron, 1939. Among those on top of the machine are Phil Abelson, Luis Alvarez, Edwin McMillan and Robert Oppenheimer.

  Back to Superman at the Manhattan Project. Schiff had refused the FBI’s request to pull the offending panels, only to be overruled by his publisher, who had a ghost writer come in and make changes. The storyline was quickly wrapped up: the hero survived his encounter with the cyclotron (‘never felt better!’) and the strip was quietly changed to something more all-American, where the Man of Steel played a baseball game single-handed. As Newsweek commented after the war, ‘Superman could take [a cyclotron bombardment] and did. What he couldn’t take was the Office of Censorship.’2

  A year before Clark Kent’s accidental espionage, Seaborg’s hand-picked unit of element hunters had already started to try and make element 95 with a cyclotron. In a host of locations – including Berkeley, St Louis and Oak Ridge – the team bombarded Pu-239 with deuterons and neutrons to try and induce neutron capture. The results were all negative. Perhaps there was a problem with detection? Al Ghiorso began to come up with new, innovative instruments to try to coax out any sign of a new element.

  Finally, in July 1944, as the Allied forces began to break out of Normandy following the D-Day landings, an idea broke out of Glenn Seaborg’s mind. What if the chemistry was all wrong?

  * * *

  Summer in Oak Ridge is hot. The hot labs at Oak Ridge’s Radiochemical Engineering Development Center (REDC) are, paradoxically, cool. The ‘hot’ in the name is a reference to the deadly amounts of radiation that lurk inside. Fortunately, in 50 years the Oak Ridge team have never broken containment. ‘You notice the doors are getting harder and harder to open as we get deeper?’ one of my guides, nuclear engineer Julie Ezold, comments. ‘The walls here are 54-inch concrete, each window has three panes of leaded glass that range between 3 to 8 inches and in between each of those is a mineral oil. Even then, the mineral oil needs replacing every 5 to 10 years. The radiation just eats it away.’

  Ezold is accompanied by Rose Boll. Both are carrying on Seaborg’s legacy of separating out the newly formed elements. Ezold is a 26-year Oak Ridge veteran who started out studying iodine, one of the most common uranium fission products. You also find iodine in your thyroid gland, which is why fallout exposure is treated with potassium iodide – you don’t want the radioactive version taking up residence in your neck. Boll came to Oak Ridge via working in a hospital as a medical technologist before going back to college and specialising in medical isotopes. There doesn’t seem to be one route to Oak Ridge’s hot labs, but once you get there, few choose to retire.

  I took a car up to the hot labs from HFIR. The newly created elements come up from the reactor via the ‘Q-ball’, a massive shielded container, painted white, that is usually suspended in water above the unloading pool floor. When the products are ready, it gets loaded on a tractor trailer and taken up the hill. It’s hard for anything to escape 25t of protective metal.

  I’m taken deeper into the hot labs’ interior. Turning a corner, suddenly we’re in a long gallery, where a row of chemical technicians are staring deep into inky, oily boxes in the wall – a series of enclosed chemistry stations called ‘hot cells’. Their hands are gripped to giant steel rods that vanish up into the roof. From there, the rods – manipulators controlled by f
lexible metal tape – reach down into the boxes with metal claws, allowing the operators to puppeteer the experiments concealed inside. It’s hypnotic to watch: a cross between the brute force of a power loader from Aliens and Tom Cruise’s graceful hand flicks in Minority Report. The workers don’t even blink as, with a twist of their wrist and a flick of their thumb, the metal claw grabs a flask of whatever they need.

  The hot labs operators work 12-hour shifts, 24 hours a day. First the aluminium is trapped in a matrix and stripped away. ‘Aluminium dissolves in base, whereas the target forms a hydroxide,’ explains Boll. ‘That’s solid. You filter it out and gather it up.’ Ezold’s eyes gleam. ‘It’s pure chemistry. Just with a bit of radiation added to it.’

  I approach and look over an operator’s shoulder, a big guy wearing a loose T-shirt and baseball cap. Trucker chic. How he can even see inside is amazing, let alone tell where the variety of leads, pipes, buttons and wires are all supposed to go. ‘It’s like spaghetti,’ I mutter, staring deep into the vortex above his station.

  ‘Yeah,’ the operator, Porter Bailey, agrees, his reply given in a deep Tennessean drawl. ‘It gets difficult sometimes. But we have maps, procedures.’ Another whirring click and a flick of his wrist, and the robot arm on the other side of the glass comes to a halt. Even with the aluminium gone, the process isn’t done. You still have to separate out the uranium, plutonium and anything else there. That means taking all the solid bits that remain and throwing them in a column of acid, where the newly made elements separate out. ‘We just dissolved 32 plutonium targets,’ Bailey says. Whirr. Click. ‘We’re giving it an acid digest for about 24 hours.’

  From this point on, nothing is wasted. Even if it isn’t the element you want, the smallest bead of it is worth more than my house. ‘We’ve been able to get material out of the hot cells in nanogram [a millionth of a milligram] quantities,’ Ezold says. ‘They [the hot labs staff] do magic … it’s science and an art.’

 

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