By Ron B. Davis Jr., Georgetown University
In 2012, after the discovery of Nihonium, to complete row seven of the periodic table there now remained the largest odd-numbered element, number 117—a real challenge. The Dubna lab group was eager to make element 117 using the magic bullet, calcium-48. However, this time it would be more challenging as the target material would have to be berkelium, a heavy actinoid with essentially no known commercial use. Could the team do it?
Berkelium
Berkelium forms in high-flux reactors, alongside californium, and though known for six decades, had not proven useful for much of anything. This meant, that, even when it was produced, it was rarely collected.
Additionally, there were only two facilities on Earth that had the ability to produce berkelium in the quantities that the team would need. One of them was a Russian reactor facility, which had expressed no interest in providing what the Dubna team needed. The other was the high-flux reactor team at Oak Ridge National Labs, in Tennessee.
Fortunately, it was Yuri Oganessian’s American friend, and collaborator, Joe Hamilton, who helped convince the Oak Ridge National Labs to provide the target sample.
The Target Material
This, however, could not be just any sample of berkelium. To make the superheavy element 117, their projectile and target would both need to be as neutron-rich as possible. That means only using the most neutron-rich berkelium isotope available—berkelium 249.
This isotope of berkelium, which forms as californium beta-decays in high flux reactors, has a half-life of just 330 days. The target material for any meaningful attempt would have to be synthesized and collected in Tennessee, shipped to Russia and bombarded with calcium-48 ions for who knows how long—all before most of the berkelium itself radioactively decayed and was lost.
After three years of waiting for a commercial order of the parent nucleus, californium-252, in December 2008 enough berkelium would be produced as a byproduct of the order for an attempt to make element 117. It would also take another 180 days to cool, process, and purify the berkelium to prepare it for transportation. Thus, unfortunately, even if everything went perfectly, about an entire half-life of the sample would already have passed by the time it even reached the reactor in Russia.
This article comes directly from content in the video series Understanding the Periodic Table. Watch it now, on Wondrium.
Refused Entry, Twice!
Even in the post-Cold War climate of the 21st century, shipping a 22-milligram sample of radioactive material from America to Russia would be no small undertaking. All of the paperwork would have to be in perfect order. It was. Unfortunately, the perfectly prepared paperwork did not make it onto the plane with the precisely prepared sample! So, the berkelium found itself on a return flight back to the United States.
And the frustration did not end there. The sample flew to Russia a second time, where the paperwork was judged incomplete, and the sample was again refused entry into Russia.
When the sample finally did arrive successfully in summer 2009, after making its third trip, the half-life clock of the sample was really ticking away! Would there still be enough berkelium to succeed?
Element 117, Tennessine
Bombardment began immediately, and after 150 additional days, in April 2010, the Dubna team achieved success. By that time about two-thirds of the berkelium that had been extracted from the Oak Ridge reactor would have already decayed into lighter elements. Nonetheless, six of the remaining berkelium atoms had been successfully converted into element 117, which was named tennessine to acknowledge the generosity of the Oak Ridge National Laboratory.
Ever the optimist, Glenn Seaborg anticipated the possibility of an eighth row for the periodic table as early as 1969. Having reached that threshold, we are close to proton numbers of 120, 122, and 124, which, like flerovium, are expected to be more stable than other superheavy elements. If a strategy to produce a doubly magic nucleus of such atomic numbers can ever be worked out, stable superheavy elements may be a real possibility.
The Periodic Table
This also poses another interesting question: does the periodic table have any final upper limit?
From a nucleus perspective, it is hard to say. But the physicist, Richard Feynman, is said to have predicted that the story of the periodic table might end at element 137 not because of unstable nuclei, but because calculations predict that electrons orbiting such a nucleus would have to exceed the speed of light just to stay in orbit.
More recent estimates, that take relativistic effects into account, have suggested there may be room to fill an eighth row that goes all the way to element 172.
However, the truth is that we don’t really know where the limit is. And yet, to conclude, it still makes sense to keep going precisely because of how much knowledge is already embodied in the periodic table-an awesome tool to guide us on our exploration of matter and the universe.
The periodic table is arguably the greatest single summary of existing human knowledge on the topic of matter. It is a complex, layered storybook filled with tales of triumph, of strife, of competition and of collaboration, all in the quest to better understand the fundamental behavior of the matter around us.
Common Questions about the Challenges of Producing Element 117, Tennessine
The isotope of berkelium, which forms as californium beta-decays in high flux reactors, has a half-life of just 330 days.
Element 117 was named tennessine to acknowledge the generosity of the Oak Ridge National Laboratory.
Richard Feynman is said to have predicted that the story of the periodic table might end at element 137 not because of unstable nuclei, but because calculations predict that electrons orbiting such a nucleus would have to exceed the speed of light just to stay in orbit.
