Most of the known elements in our universe were created in the white hot cauldrons of exploding stars, and hurled across time and space for humans to eventually discover.
For much of the 18th and 19th centuries, chemists enjoyed a harvest of low-hanging fruit that saw new elements regularly discovered and added to the periodic table. In 1898, Sir William Ramsay and Morris Travers isolated Krypton, Neon and Xenon over just six productive weeks, establishing the noble gas family of elements that would go on to drive the development of lights, lasers, and photography.
The pursuit of new elements today, is a herculean task.
Now, the process requires global research teams to work with billion-dollar machinery on experiments that can last years — to create something that exists for just a fraction of a second.
“It is very patience oriented…and it can be exciting,” says Dawn Shaughnessy, principle investigator of the Heavy Element Group at the Lawrence Livermore National Laboratory in California.
But the often gruelling work can deliver spectacular payoffs.
“Understanding how this works, somehow translates to how the universe is continuing,” says Shaugnessy.
New chapters
In January 2016, four new elements were confirmed by the International Union of Pure and Applied Chemistry (IUPAC), completing the seventh row of the periodic table. This represented the most significant overhaul in decades, rendering text books across the world obsolete.
Three were credited to Shaughnessy’s group, along with partners in Russia and Tennessee. Her group has now claimed five of the last six discoveries, and had the honor of naming element 116 Livermorium. These are rewards from two decades of exploration.
“Now we have discovery rights we can think about names,” says Shaughnessy, without giving away what these might be.
Elements are listed by atomic number in the periodic table, which corresponds to the number of protons (positively charged particles) in their nuclei. The heaviest naturally occurring element is uranium, with 92 protons, and beyond it lie super-heavy elements that don’t exist naturally and must be synthesized. These elements are rendered highly unstable by their weight of protons, which generate a powerful repelling force that tears the nucleus apart.
To create super-heavy elements requires nuclear fusion, blending elements together to form a new creation, which Shaughnessy’s group has mastered in partnership with the Joint Institute of Nuclear Research (JINR) in Dubna, Russia.
Nuclear testing
In their search for these unstable elements, the researchers smash billions of microscopic particles from two lighter elements together inside a cyclotron — a type of particle accelerator – at the JINR, hoping that two particles will fuse. The experiments can last several months.
In each case, the team uses elements with atomic numbers that add up to the target. The as yet unnamed element 117 was created by firing beams of calcium atoms, containing 20 protons, at a layer of Berkelium, containing 97.
When a successful fusion occurs, the new element is sent flying through a separator that filters out any other particles, before arriving inside a detector lined with silicon sensors. These sensors then send electrical signals for the scientists to decode as soon as possible, while the unstable product rapidly decays — usually within seconds. Most signals mean nothing and simply represent background particles, or false events.
“We have to find a signature,” says Shaughnessy. “If we are lucky, two or three times over the course of an experiment we get a series of numbers that look like they came from the same element — the right lifetime, the right energy, the same location in the detector,” she says.
At that point, collaboration is key. The Russian and American teams swap notes and compare data, working to eliminate any other possibility — before repeating the test.
“If you get a couple more of the same results, then it hits home that you’ve discovered something new,” says Shaughnessy.
The end of the line?
It can take years to produce a super-heavy element, and just seconds for it to disappear.
This fleeting lifespan make studying the elements impossible, and their applications questionable, but their instability offers insight into the nature of matter.
“At this point we can’t say much about what the elements could be used for,” Shaughnessy admits. “But they are telling us how matter itself holds together.”
The extreme limit of matter could also give rise to new theories of the evolution of the universe.
“When we figure out where the end of the periodic table is, we will know where matter ceases to be, which is important to understanding the universe.”
Predictions vary over how many more elements could be added to the periodic table, with one model suggesting 172.
Researchers in the field continue to search for elements 119 and 120, but any further discoveries would require a dramatic improvement of technology.
The Flerov lab at JINR will introduce a more powerful cyclotron later this year, but Deputy Director Dr. Andrey Popeko is skeptical that this will yield new elements.
“(With) the existing accelerators, the production rate of element 118 is one atom per month,” says Popeko. “The new accelerator will possibly increase this rate to one atom per week. We also plan to search for heavier elements, but there are experimental indications that elements beyond 118 do not exist.”
In search of an island
The holy grail for Shaughnessy, and the field of heavy element chemistry as a whole, is to find the “island of stability” – a theoretical island where elements are no longer unstable.
The theory dates back to the 1960s and Nobel-prize winning chemist Glenn T. Seaborg,
It predicts that an isotope — a variant of an element with a different number of neutrons – of a super-heavy element could be engineered with a perfect balance of protons and neutrons neutrons (sub-atomic particles with no net charge), which would give it lasting stability, perhaps even for years.
Scientists have estimated the island’s location based on the most stable existing elements and isotopes, and Shaughnessy believes she is getting closer.
“As we went up to element 114 we did see longer lifetimes equating to more stability, and then down again to 118, which was very short-lived.”
The longer lifetimes seen were still seconds, but when averaging milliseconds this is plenty of time.
Shaughnessy believes 114 is the most likely destination. Tinkering with the composition of atoms in this element specifically, to find the perfect formula, has now replaced element discovery as her most urgent priority.
“If we push out the number of neutrons we might be able to get there,” she says.
A stable, super-heavy isotope would allow for comprehensive study and could give rise to new technologies.
“If there is an island of stability and we hit it, we can determine if the (isotope) has unique properties,” says Dr. Lynn Soby, ?Executive Director of IUPAC. “It could be similar to iodine-125 that lead to diagnostics for disease through nuclear medicine.”
Breaking boundaries
As one of the most senior female figures in one of the most demanding scientific disciplines, Shaughnessy feels a responsibility to encourage young women to pursue careers in science.
As a student at the University of California at Berkeley, Shaugnessy benefitted from studying under an ideal mentor in the celebrated nuclear chemist Darleane Hoffman.
“There were no women in management at the time,” recalls Shaughnessy. “She had a totally normal life – she had kids, she went traveling. She showed me you could do it.”
Now, Shaughnessy hopes to have a similar catalytic effect and serve as a role model for a new generation of women in an otherwise male-dominated profession.
“Young girls tell me I don’t look like a scientist, which is a compliment. I tell them that I love science but it’s a job and it doesn’t define me as a person.”
Shaughnessy worries that the field is shrinking in general, with fewer students training for nuclear chemistry. Attracting new talent is therefore critical, but challenging.
The word “nuclear” can be a public relations liability, as many prospective students are put off by its negative associations, but chemistry in popular culture can be a powerful recruitment tool, says Shaughnessy. She saw increased interested after the popularity of “Breaking Bad.”
The field of element discovery may face an uncertain future, but Shaughnessy’s place in history is already secure.
