Protons don’t like to stick together for long. But if you have the correct number neatly distributed among enough neutrons, they may well be able to build an atom that won’t break apart in the blink of an eye.
Theorists had suggested that 114 could be such a “magical” number of protons – but a recent experiment conducted at the GSI Helmholtz Center for Heavy Ion Research in Germany now makes that incredibly unlikely.
In 1998, Russian researchers finally managed to build an element with 114 protons in the nucleus. It was later named flerovium after its hometown, the Flerov Nuclear Reactions Laboratory of the Joint Institute for Nuclear Research.
Making mammoth-sized atoms is certainly not easy, just by starting with heavyweight elements like plutonium and pelting them with something smaller, like calcium, until something sticks.
By ‘sticks’ we mean ‘pauses long enough for an atom to technically pass’, which for nuclei the size of a mountain is rarely more than a fraction of a second. For example, with a size of 112 protons, the transuranic element of copernicium has little chance of lasting longer than 280 microseconds.
Atomic nucleons hold each other as an effect of the strong force shared between the trios of subatomic quarks that make them up.
At the same time, the repulsive nature of positive charges in protons push them apart, meaning that the entire structure teeters on the verge of collapse if they get too close together. Therefore, we see some combinations of nucleons or isotopes more often than others.
Once an atom has reached a certain size, a whole host of other factors related to energy and mass also weigh in, making it increasingly difficult for the atom to hold itself together, not to mention the harder for physicists to predict its characteristics.
Still, physicists are convinced that there are islands of stability in the upper reaches of the periodic table, where proton arrangements can form patterns and shapes that allow them to sustain life a little longer than neighboring elements.
For example, nihonium, or element 113, has an isotope with a half-life of about 20 seconds.
However, when signs of flerovium were first sifted from a plutonium and calcium debris over 20 years ago, it looked like a real keeper. The signature in the data suggested that atoms remained stable for up to 30 seconds before spitting out an alpha particle and crumbling briefly in copernicium.
The excitement was short lived. In 2009, Berkeley scientists managed to recreate two different isotopes of the element. One of them lasted a tenth of a second. The second lingered a bit longer and fell apart after half a second.
The odds weren’t good for element 114, but physicists aren’t the type to leave well enough alone. So the University of Mainz got big and used improved detectors to study dozens of possible flerovium decay events.
Ultimately, two were confirmed as bona fide isotopes. One resulted in a copernicium isotope that was broken down in a way that had not been observed before.
In that case, the flerovium decay chain took place within 2.4 seconds, in a secretion of alpha particles. The second isotope disappeared in 52.6 milliseconds. Importantly, the efficient way each of the two isotopes decayed revealed that 114 was not stable at all.
Exciting as a stable flerovium may be, the new findings of an excited state of copernicium provide a solid foundation for exploring islands of stability higher up the periodic table, providing theorists with vital information to further model this phenomenon.
“The existence of the state provides yet another anchor point for nuclear theory, as it appears to require an understanding of both coexistence of shapes and shape transitions for the heaviest elements,” the researchers note in their report.
While we can now almost rule out 114 as one of the magical numbers of the periodic table, there are still more giants to defeat.
Physicists have yet to create the hypothetical element that is tentatively called unbinilium or element 120. Making one of those samples would require some powerful technology and advanced knowledge of nuclear physics.
Plans are underway to push the boundaries of atomic mass, with RIKEN in Japan making steady progress at its Nishina Center for Accelerator-Based Science, so we may not have to wait long.
Like explorers of yore, researchers are still convinced that there are stable islands just above the horizon. We will no doubt see some mirages along the way.
This research is published in Physical Review Letters