By Ron B. Davis Jr., Georgetown University
New calculations showed that element 114 was expected to have a magic number of protons, and just might have a the ‘island of stability’, a predicted zone of much higher mass on the nuclear stability curve that might harbor stable elements with magic numbers of nucleons. In order to make element 114, Yuri Oganessian decided that it was time to switch back to hot fusion, shooting highly accelerated particles at targets to form heavy elements. Did it work?
Calcium-40, the Magic Bullet
When it came to element 114, there was just one problem. Alpha particles wouldn’t work this time. In order to make element 114, the earlier superheavy elements themselves just weren’t realistic candidates for targets.
However, technology had progressed since the days of alpha bombardment had opened the door to synthesis of the trans-plutonic actinides, and a new ‘magic’ projectile was available that solved the problem.
That so-called ‘magic bullet’ was calcium-48. With 20 protons and 28 neutrons, calcium-48 is a doubly magic nucleus, making it unusually stable and thus, able to survive the energetic collisions associated with hot fusion. Secondly, the high neutron-to-proton ratio of calcium-40 helps to deliver more neutrons to new superheavy nuclei, increasing the chances that they will be close enough to the stability curve that they are stable enough to form, even if for an instant.
And finally, with an atomic number of 20, all of the remaining superheavy elements in row 7 could be formed using actinoid targets—elements long-lived and available enough to make setting up the experiment possible.
Using this newly selected projectile of choice, Yuri Oganessian’s team succeeded in fusing neutron-rich calcium-48 with plutonium-244—that’s 20 plus 94—to form element 114. The ‘magic’ bullet had worked. It was an exciting moment for both the Russian and American teams, who after the Cold War ended had become collaborators more than rivals in the superheavy synthesis game.
The single atom of element-114, with a total of 289 neutrons and protons, lasted a mind-boggling 19 seconds. It was promptly named flerovium-289, in honor of Georgy Flerov, who had died in 1990, but who had played such an important role in founding and leading the Dubna group for decades.
This article comes directly from content in the video series Understanding the Periodic Table. Watch it now, on Wondrium.
If the climate between the American and Russian labs of the late 20th century had been described as the transfermium wars, one might as well describe that of the early 21st century as the ‘trans-copernicium alliance’.
In 1999, authors from the Joint Institute for Nuclear Physics, in Dubna, Russia, and from Lawrence Livermore National labs, near Berkeley, in the USA, both appeared in the by-lines of a single article claiming shared credit for the discovery of Flerovium.
In the year 2000, it happened again, this time on a paper claiming that element 116 had been prepared by the bombardment of curium with calcium-48. Shortly thereafter, yet another collaboration produced element 118, from californium, using the same method.
And while the American-Russian collaboration would endure to the end of filling row seven, global controversy and competition over discovering superheavy elements were not yet, at an end. A new competitor was about to enter the fray—the nation of Japan.
Destroying the Japanese Nuclear Research Program
In the wake of the atomic bombings of Hiroshima and Nagasaki, and the subsequent Japanese surrender, Allied forces were highly suspicious of the Japanese nuclear research programs. Thus, just after the World War II, the Allies ordered every cyclotron in the nation of Japan destroyed. The decision earned the ire of not only Japanese researchers, but of Americans as well. Scientists at Oak Ridge National Labs publicly decried the decision, calling it “wanton”, “stupid”, and even “a crime against mankind”.
The outcry may have prevented a further plan to completely dismantle all research capabilities at Japans’ national lab, known as RIKEN.
Japan, devastated and destitute, took until the 1990s to rebuild its reputation and its equipment to the necessary level to compete.
It was in 1992, that RIKEN researcher Kosuke Morita made a fateful trip to Dubna, Russia, to work under none other than Yuri Oganessian. While Morita studied, RIKEN scientists constructed their own ion accelerator. By the time he returned, RIKEN was ready to take its shot at immortality on the periodic table by attempting to produce element 113.
As RIKEN’s methods were still a bit behind they relied on Oganessian’s low-energy fusion techniques. In 2004, they bombarded bismuth with zinc ions—83 plus 30—and observed decay products consistent with element 113.
A Two-for-one Discovery
Next, the American and Russian team produced element 115 using the magic bullet calcium-48 and Americium targets. In an exciting additional development, their element 115 appeared to decay into element 113 through an alpha emission. It was a two-for-one discovery for the Americans, and RIKEN’s claim to discovery was in real peril.
The race was on for both sides to shore up their data and stake their claim to 113. The final experiment, that put the RIKEN team over the top, was conducted in the aftermath of the Fukushima nuclear power plant disaster of March 2011. In the wake of that national catastrophe, energy prices surged in Japan, making the accelerator at RIKEN all the more expensive to run.
But in a twist of fate, that actually worked to their advantage. Many other RIKEN experiments were cancelled, and Morita’s team would actually have access to more time with the sought-after device, looking and listening for element 113 a second time.
Not long after the disaster, in 2012 the team successfully detected the decay of element 113 again, earning the nod for the discovery from the IUPAC and cementing their rights to name their creation. They chose Nihonium, which is a Japanese way of saying ‘japanium’.
Common Questions about the Trans-Copernicium Alliance and the Japanese Discovery of Nihonium
The so-called ‘magic bullet’ was calcium-48. With 20 protons and 28 neutrons, calcium-48 is a doubly magic nucleus, making it unusually stable and, thus, able to survive the energetic collisions associated with hot fusion.
Just after the World War II, the Allies ordered every cyclotron in the nation of Japan destroyed.
Element 115 appeared to decay into element 113 through an alpha emission. It was a two-for-one discovery for the Americans.