by Kit Chapman
In 2005 Oganessian contacted Joe Hamilton at Vanderbilt University, based in Nashville. The duo had worked together for nearly 20 years and had published 200 papers together. Hamilton, not giving a damn about the Cold War, had made his first trip to the USSR in 1959 and had spent more than six months of his life in Russia. He also had ties to Oak Ridge. ‘We went and talked to the people at the High Flux Isotope Reactor,’ recalls Hamilton. ‘They said the only economical way to get berkelium was to piggyback a commercial company order for californium-252.’ There was only one problem: there was no commercial order for californium-252 at the time.
Hamilton didn’t give up. He phoned Oak Ridge every three months for three years. His tenacity became the stuff of legend. ‘He pounded on the door,’ remembers Mark Stoyer. ‘“Can we get berkelium? Can we get berkelium?”’
In August 2008 Hamilton’s dedication finally paid off: there was a californium campaign scheduled at the reactor. The next month, Oganessian flew over to Vanderbilt to celebrate Hamilton’s 50 years of research in atomic physics. There, among the canapés and polite conversation, the American told him the good news. Still finishing their lunch, they invited Oak Ridge’s associate director, James Roberto, to join them. Roberto listened to their plan for the element and realised its potential. Soon, Oak Ridge, JINR, Vanderbilt University and Livermore (contributing some of the costs of making berkelium) and the University of Tennessee, Knoxville were working together.
In December 2008 a californium run at HFIR in Oak Ridge produced the 22mg of berkelium. The teams were on the clock: the sample had a half-life of 327 days. It took 90 days to cool the sample, then 90 days to purify it. Next, it had to be prepared for transport. First, it was dried into a solid form (berkelium nitrate) and slipped into a glass vial. This was swaddled in chemical wipes (for shock absorption) and placed inside a lead pig – a carrying container about the size of a coffee flask. Finally, to complete the package, the pig was sealed and placed inside a drum, which was sealed again. ‘And that’s your Department of Transportation certification,’ Oak Ridge’s Julie Ezold told me. ‘Then it’s literally like FedEx.’
At least, it should have been like FedEx. ‘In this particular case, since it was going to Moscow, it went to JFK Airport, New York. It flies over to Moscow. And [the group] had spent months trying to get the documentation prepared for this. The documentation didn’t make it on the airplane. So, it came back. We fixed that, and it goes back over again … and something in customs wasn’t right. Again, it comes back. So, we are very concerned, fighting the half-life, of how many trips this took across the ocean.’
The fifth flight proved lucky – after 25,000 air miles, the berkelium made it to Dimitrovgrad, where the target discs were to be prepared before heading on to JINR. Even then, a Russian customs officer tried to open the package and check the contents. Luckily, some of the Dubna team were on hand to convince the official he really didn’t want to see what was inside.
The Delta pilots who shipped the vial, and the Russian customs officers who tried to check them, probably don’t know they helped to write the final chapter to date of chemical element discovery. After firing their calcium-48 beam into the berkelium for 150 days, the Dubna–Livermore team announced 6 atoms of element 117 in April 2010. In 2012 they did it again. In 2014 GSI confirmed their data. Element 117 had been found. Its half-life was a mere 50 milliseconds, but this was still far longer than would have been predicted if the island of stability were a myth. The new element’s alpha decay chain matched up with the results from the search for 115 too, confirming the validity of the experiment.
In 2012, when the experiment was repeated, the team got a surprise. A small amount of their berkelium target had beta-decayed into californium. As well as producing yet more atoms of 117, the team also hit one of these rogue spots of californium – resulting in yet another atom of element 118. It had a half-life of less than a millisecond – but it was yet more evidence that Livermore and Dubna, with a little help from Oak Ridge, were the new masters of creating the different components that make our physical universe.
In December 2015, when the IUPAC/IUPAP joint working party announced that element 113 had been granted to RIKEN, they also announced that elements 115, 117 and 118 had been discovered by the Dubna-led team, with 118 being awarded to Dubna and Livermore.1
Yuri Oganessian had led a collaboration that stitched together 72 scientists from 6 institutions around the world. The team had been awarded the discovery of five elements. The seventh row of the periodic table, something that had remained partially complete for more than a century, had finally been filled.
On 23 March 2016 the collaborators held a conference call to discuss the names of the new elements. First, 117: it would be ‘tennessine’, honouring Oak Ridge and the contributions that had come from across the entire state. Next, 115: ‘moscovium’, after Dubna’s home state.
Livermore had wine. Dubna had vodka. RIKEN had sake. When Oak Ridge found it had a new element, lead physicist Krzysztof Rykaczewski popped to the Jack Daniel’s distillery in Lynchburg and ordered up some Tennessee sippin’ whiskey. Ask Ezold, Rykaczewski or any of the Oak Ridge scientists the proudest achievement in their career, and they’ll tell you it’s discovering a new element. It’s not just for them, either. ‘I have an eight-year-old daughter,’ Ezold told the Farragut Press when the names were announced. ‘For me to be able to say I was part of the discovery of a new element is off the charts.’ Powering space probes or helping to land a rover on Mars doesn’t even come close to being a mum who helped make and name a piece of reality.
Do names really matter? Again, Sigurd Hofmann’s answer is perhaps the best. ‘Partly, I suppose it is because everyone feels qualified to give an opinion, and partly because they become very proprietary and emotionally involved. It is, after all, the very centre of the lives of people doing it.’
Element 118 was about to become the very centre of one man’s life in a way he could never have imagined. After tennessine had been named, Yuri Oganessian was asked to step out of the room. Then, with every other scientist’s agreement, the Dubna–Livermore collaboration decided he would follow in the footsteps of Glenn Seaborg. Element 118 would be ‘oganesson’.
‘Phew.’ Oganessian blows out his cheeks when he thinks about the honour. His eyes widen with
emotion, pupils blinking with a thin film of tears. ‘It’s difficult to say how I feel. Because it was
proposed by my collaborators. All of these people were involved and came to this conclusion after all the elements we synthesised. Of course, it’s an honour for me. But it’s my friends and colleagues who want to express it. I’m just seeing that there are a lot of things yet to do, even with this element. It’s not the final piece of the story.’
Some people dream a little bigger. And, like the Japanese, Oganessian hasn’t finished dreaming yet. He’s going after elements 119 and 120 too. And this time he has even more help.
* * *
It’s easy to get the impression that element discovery is only about the labs where the elements are made. This is a complete illusion. The elements were made in Berkeley, Dubna, GSI and RIKEN – but without partnerships or the flow of personnel and ideas, we’d still be stuck with a periodic table ending in uranium.
Today, the superheavy world isn’t just defined by discovery. There are a multitude of other labs, in France, Japan, the US, the UK, Sweden and Poland, where outstanding work is being done by brilliant scientists to contribute to a greater whole. It’s part of the reason I’ve made the longest leg of my superheavy journey, all the way to see an accelerator in Canberra, Australia. Here, one team is trying to map out the path to the undiscovered elements – 119, 120 and beyond. I just hadn’t counted on the Aussie weather: Australian National University (ANU) is flooded.
Canberra is an artificial city, a compromise capital to stop Sydney and Melbourne arguing about who is better. Set in lush hills and split by an artificial lake, Canberra’s manicured lawns
and far-too-organised streets feel over-engineered compared with the organic blossoms of Berkeley or Dubna. Yet unfortunately for the Australian government, even a city planned to perfection is at the mercy of the weather. Last night, as I fought off jet lag from a 24-hour flight, 2 months of rain fell in a matter of hours, bursting Sullivans Creek and dousing the ANU campus in rainwater. Officially, everything is closed – even the redback spiders have scurried for higher ground. But beam time is too precious to let a little thing like a deluge stop the work. The ANU accelerator is up and running – and that means I can make my visit.
Despite the university supposedly down to a skeleton staff, almost every single member of the department has come in to meet me. The ANU team are close-knit, a mix of young and old sharing a small office building on the fringes of campus, just a short walk away from their particle accelerator. Camaraderie is high: when three of the professors wanted to give their technical staff more opportunities, they pooled their own money to create a fund to get them to overseas conferences. The relaxed atmosphere extends to the break room. Here, visitors can find two fridges adorned with signatures of departing visitors. ‘Those are our beer fridges,’ one team member tells me, as if it’s the most natural thing in the world. ‘When you leave, you’ve got to try and fill the fridge with beer. If you manage to do it, you get to sign your name.’ Welcome to science the Australian way.2
The relaxed, friendly feeling continues when you go across to the accelerator itself. The control centre is a single room with beaten sofas and an old-school accelerator control console first used in 1968. Even so, you soon realise just how staggeringly complex it is to run, fund and house even a small heavy element facility. The ion accelerator – that first push for your particle cannon – is kept vertically in a tower, dropping down a 33m (108ft) tank filled with 20t of sulfur hexafluoride gas to prevent the 14MV of charge sparking off against the wall. Shooting down at around 35,000km (22,000 miles) per hour, the beam is then bent by magnets into the horizontal plane (using the Lorentz force, the same way a cyclotron’s beam is bent) and either directed out for experiments or – if they need the extra kick – into the superconducting linear accelerator itself, where it’s sped up using the same beam pulses found at GSI. The shape of the accelerator is a little different, though: cramped for space, the ANU team have bent it around in several loops, the beam line twisting its way to take up virtually every spare inch of the accelerator hall before swinging out toward its target. It’s like a game of Snake, in which you’re forced to either climb over the pipes or scramble under them to get to the other side of the lab.
‘Some people said it was cursed,’ remarks David Hinde as we step up above the linear accelerator. The director of the Heavy Ion Accelerator Facility, he’s leading my tour with experimental physicist Nanda Dasgupta. ‘The accelerator came originally from Daresbury [a nuclear physics laboratory in the UK], and before that Oxford University, after they took a funding hit. We were fortunate to get it, but everyone who had it ‘fell over’ [ran out of funding] – it had been at two different labs but had never really been used. Anyway … the beam comes down from the tower, bends into a horizontal plane, around a bend – which is preeeeety difficult, very particular entry, very acrobatic – and then it comes in here …’
At a larger laboratory, the chemists and physicists are often hands-off with the equipment – they just worry what’s going on with their beam line. Without the funding for technicians to run the accelerator around the clock, Hinde, Dasgupta and their students adjust the beams, magnets and ion source themselves. The upside, Dasgupta says, is that you can fiddle around and make small adjustments to perfect your set-up on the fly. ‘If you see something unusual, you can just change it,’ she enthuses. ‘Last week I was in the tea room and someone said, “Oh, it’d be good to measure this, when can you do it?” And I told them: “Tomorrow!”’
The ANU mantra is to be low-cost but high-precision. Dasgupta passes me a metal square frame. Inside, a 1cm2 circle is filled with graph paper. Holding it up to the room’s fluorescent lights, I can see a pinprick hole burned through it. ‘That’s the size of the beam spot,’ she says. A little further on, we come to the experimental equipment at the end of the beam lines, including a Faraday cup to catch the beam. It’s a mere 4.5mm in diameter. The fusion detectors, designed at ANU, use thousands of 20-micrometre tungsten wires, coated in super-high-quality solid gold. They’ve been shipped from Norway, where they had originally been made for CERN. Once again, the Canberra team had to make the equipment themselves, although Hinde didn’t mind. ‘I was of the Airfix generation,’ he says, wiggling his eyebrows. ‘I used to make Second World War airplanes and tanks. When someone tells me you can’t do something a certain size, I say “sure you can”.’ If you can stick a rear-view mirror into the cockpit of a scale model Spitfire, you can make a fusion detector.
The set-up isn’t as powerful as the leading labs’ machines. Its kit can’t reach the staggering sensitivity needed to get down to picobarns. But ANU doesn’t need it. It might be small and on a shoestring compared with the bigger labs, but it still punches above its weight. Currently, it’s a world leader on quasi-fission – providing essential clues about why nuclei generally fail to fuse together. ‘We’re known for our fusion work,’ says Dasgupta. ‘We also look at tunnelling, well below the fusion barrier.’ This is essential for fusion in stars, where the energy provided by pressure and temperature isn’t enough to push past the Coulomb barrier. The trick is known as quantum tunnelling: when you hit the subatomic levels, things get weird and start acting like waves, allowing particles to slip through.3
While ANU’s experiments can’t create new superheavy elements – there’s not enough beam intensity and the university lacks the multi-million-dollar infrastructure needed to handle highly radioactive targets – it does mean the scientists can provide clues about where and how to look for them. The Australian team use their accelerated beams to work out the best ways to form superheavy elements: what energies are needed and how the reactions will behave. I remember Jacklyn Gates talking about magnets being just 6 per cent out of alignment; ANU’s work means the element hunters now have a better idea about what beams and targets to try, and where to look. ‘It’s like Where’s Wally,’ Dasgupta explains. ‘Wally is hidden somewhere in a load of pirates. We’re getting rid of the pirates, taking Wally and putting him in the detector.’
Thanks to the work by Hinde and Dasgupta, we understand how stable and unstable nuclei work, why our world can cling together. It also provides clues as to how our world changes when we move from the subatomic, quantum world with its own rules and forces, through to the classical physics we’re more comfortable and familiar with.
More importantly, they help with games of ‘element Where’s Wally’. And when it comes to the hunt for new elements, scientists need all the help they can get.
* * *
In 2013 sitcom character Sheldon Cooper figured out a way to synthesise element 120. Less than 10 minutes later (not including ad breaks), a team in China used a cyclotron to confirm his discovery. Then, Amy Farrah Fowler, Cooper’s equally fictional girlfriend, pointed out that he’d made an error by a factor of 10,000. ‘I’m not a genius, I’m a fraud,’ Cooper whined. ‘Worse than a fraud, I’m practically a biologist.’ Despite Cooper’s protests, the world of The Big Bang Theory is still doing one better than reality when it comes to discovering elements.
The funny thing, at least for nuclear scientists, is the sprawl of calculations on Cooper’s whiteboard. Every single one of them is a plausible way to create element 120. And every single one of them (except Cooper’s supposed breakthrough using mendelevium – its half-life of 51 days means it just doesn’t hang around long enough to make a good target) has been tried in real life. So far, no new element.
The big problem with finding element 120, or even 119, is that there’s no immediately obvious way to do it. While calcium-48 is an amazing, neutron-rich beam, to make element 119 y
ou’d need a target made from einsteinium, which is currently only produced in nanograms at a time. ‘In principle, it’s not impossible,’ insists Oak Ridge’s James Roberto. ‘If we were able to take a reactor and run it in a very special mode and seed it with a gram of californium – and all of those are multi-million-dollar ifs – we could make about 40mg. That would be 0.1 centimetre square of a target, about the size of the beam itself. The challenge is that if we could get this project together, you’d still need to make a target that could take the whole beam in one spot for months at a time [without burning up].’
It’s a lot of money for a lot of uncertainty. RIKEN is currently shooting vanadium into curium. The other promising idea, which the Dubna–Livermore group is working on, is to use a titanium-50 beam (six extra neutrons), shot into berkelium. Neither option is as good as a calcium-48 beam with its eight extra neutrons; the only question is which team’s approach will succeed first.
Both teams are getting the material for their targets from Oak Ridge. But nobody knows which team is likely to push the superheavy elements onto the eighth row of the periodic table first. ‘We’re not quite stuck yet,’ Roberto says, ‘but the breakthrough is not obvious.’
The options to make the next elements don’t end with Oak Ridge’s reactor, RIKEN or at the bottom of Sheldon Cooper’s whiteboard. In 2011 Sigurd Hofmann’s GSI team tried to find element 120 using a chromium beam into curium. At around 4.20 a.m. on 18 May, they saw … they don’t know. ‘We saw something,’ Hofmann hedges. ‘Part of a decay chain that agrees with data from Dubna in around 2000. But later these data were no longer mentioned. So far, it’s not confirmed.’ As always, the world of element hunting has lots of possible routes to success; it’s backing them up that’s the hard part.
There are other ideas. Roberto has suggested reversing the reaction, building the target out of the lighter element (for example, iron) and shooting it with a beam using plutonium ions. It’s possible, although the beam intensity will be far lower, making finding an element that much harder. It also has a big drawback: shooting plutonium through an accelerator would contaminate it with radiation for 1,000 years. ‘It’s not science fiction,’ Rykaczewski promises. ‘You just need a reasonable accelerator that’s closing down … then it’s the perfect experiment.’ Another option is to shoot two heavy nuclei into each other, such as throwing curium into uranium and hoping that as the two bounce off a few protons and neutrons get transferred in passing. It’s a technique called multi-nucleon transfer. Again, fine in theory – and could even provide a bridge to the island of stability if you used isotopes with enough neutrons. Sadly, it has a major drawback: the amount of fission noise you’d get from the reaction would make it virtually impossible to see (and more importantly, prove) you’ve made your new element. It’s another reason why work from the likes of ANU is so critical.