Element 99 — mysterious and exceptionally radioactive — sits inconspicuously in the bottom row of the periodic table. Named for legendary physicist Albert Einstein, einsteinium has been one of the most challenging elements to study since it was discovered in 1952 in the airborne debris from the first full-scale hydrogen bomb explosion.
Now, nearly 70 years later, scientists have measured einsteinium for the first time, finally providing a close look at the element’s chemical properties and how it behaves. The researchers said the findings help shed light on this radioactive metal and other so-called transplutonium elements that occupy the fringes of the periodic table. These scarce materials could also themselves be used to discover brand-new elements with even more exotic properties.
“That’s kind of the holy grail of nuclear physics,” said Rebecca Abergel, a chemist at the Lawrence Berkeley National Laboratory and co-leader of the research published Wednesday in the journal Nature. “If we can produce superheavy elements — newer elements that we haven’t been able to isolate yet — that would get us closer to understanding the fundamental properties of matter.”
But first, scientists need to better characterize the elements that do appear on the periodic table.
“Not much is known about einsteinium,” Abergel said. “When we get to the bottom row of the periodic table, there’s just not enough data. By learning and understanding chemical features of the elements in this region, we can infer properties across the periodic table.”
Elements that occupy the same row as einsteinium are known as actinides. All of the elements in this series are radioactive and only two, thorium and uranium, occur naturally. Actinides like einsteinium behave very differently from other metals in the periodic table, but they are difficult to study because they have to be created, typically as a by-product of nuclear reactions.
Abergel and her colleagues were able to study a tiny amount of einsteinium that was made at Oak Ridge National Laboratory’s High Flux Isotope Reactor by bombarding a heavy metal known as curium with neutrons. The Oak Ridge lab is one of only a few places in the world that can produce einsteinium, and the facility’s nuclear research reactor enables scientists to create these radioactive metals without detonating a hydrogen bomb.
“These are advanced techniques that were not available in the 1960s, or even a decade ago,” Abergel said.
The researchers conducted their experiments using a microscopic amount of einsteinium-254, which has a half-life of 276 days, meaning it takes 276 days for half of the material to decay. Abergel’s team measured what’s known as the bond distance of einsteinium-254, which informs how the metal interacts and binds to other molecules. She said einsteinium’s bond distance was shorter than the scientists expected, but it’s not yet understood why.
“This was surprising based on what we’ve observed with other metals,” she said. “We’re now starting to speculate about why this is happening.”
Most of the team’s work was conducted between January and March 2020, Abergel said, shortly before the first stay-at-home orders were enacted in California to contain the coronavirus pandemic. But einsteinium-254’s half-life meant that roughly 7 percent of the sample was lost each month that ticked by during the lockdown.
“By the time we got back into the lab, there wasn’t enough left to do some of the chemical and spectroscopy experiments that we had planned,” she said.
Still, Abergel said her team are hoping to carry out more research on einsteinium and other actinides, which could have important applications for nuclear power production and for the medical industry.
“When we get results like this, it’s exciting because it shows how much we’ve advanced science over the past few decades,” she said.