Exploring Einsteinium

For the first time ever, US scientists have studied the properties of einsteinium – the highly radioactive, short-lived 99^th element.

The periodic table is a familiar sight to most people, but of its 118 elements, only 94 occur naturally.

The rest have only ever been synthesised; you’re not likely to find lumps of them lying around – some are so unstable that they’re more like flashes in the mind of a theorist than reality, lasting an infinitesimal fraction of a second before literally falling apart.

Einsteinium is one of these volatile and transient elements. A soft and silvery metal, it was first discovered in 1952 in the debris of the first hydrogen bomb. Though it lasts longer than many other elements – the isotope used in this new paper has a half-life of 276 days – it is still very difficult to study, as it’s hard to create and highly radioactive, making it dangerous to humans.

Researchers led by the Lawrence Berkeley National Laboratory, US, have managed to study some of this element’s properties for the first time.

Their paper, published in Nature, describes how they synthesised around 200 nanograms of einsteinium – for comparison, a single human cell weighs about one nanogram – and studied it using X-ray absorption and luminescence spectroscopy.

“There’s not much known about einsteinium,” says co-lead researcher Rebecca Abergel, from the Berkeley Lab. “It’s a remarkable achievement that we were able to work with this small amount of material and do inorganic chemistry.

“The more we understand about its chemical behaviour, the more we can apply this understanding for the development of new materials or new technologies, not necessarily just with einsteinium, but with the rest of the actinides too.”

Actinides are a subset of the periodic table, comprising 15 elements that are metallic and radioactive – including uranium and plutonium. Only six are produced in nature, while the others are purely synthetic elements.

For Abergel and team, even getting their hands on einsteinium to study was an uphill battle. It was synthesised at Oak Ridge National Laboratory, one of the few places capable of undertaking the process, which involves bombarding curium (another actinide) with neutrons to trigger a chain of nuclear reactions – while trying with difficulty to keep the sample uncontaminated.

To add to the challenge, the COVID-19 pandemic shut down their lab halfway through experiments. Given its half-life of 276 days, the einsteinium isotope they produced was mostly gone by the time the team returned to the lab.

But with this microscopic amount, they were still able to measure einsteinium’s bond distance, as well as behaviours of the element that differ from other actinides.

“Determining the bond distance may not sound interesting, but it’s the first thing you would want to know about how a metal binds to other molecules,” says Abergel. “What kind of chemical interaction is this element going to have with other atoms and molecules?”

Understanding these properties can give us a better idea about how actinides as a series behave – which may have useful implications for nuclear power production or radiopharmaceuticals.

The research is also edging onto the horizon of the periodic table and opening up possibilities to discover new elements. By isolating enough pure einsteinium, researchers may be able to bombard it with particles to induce decay – and see what other elements can be created.

“Our results highlight the need to continue studying the unusual behaviour of the actinide elements, especially those that are scarce and short-lived,” the researchers conclude.

The Royal Institution of Australia has an Education resource based on this article. You can access it here.