After 69 years, chemists finally get a good look at Einsteinium

First conceived during the combustion of a hydrogen bomb on Elugelab Island, in the South Pacific, in 1952, the heavy element einsteinium is one of the more timid members of the periodic table; it does not occur naturally and is so unstable that it is difficult to get enough of it, long enough, to study it.

Now, a team of chemists from Lawrence Berkeley National Laboratory, Los Alamos National Laboratory, and Georgetown University have managed to do just that. They inspected a microscopic amount of einsteinium-254 to gain a better understanding of the basic chemical properties and behavior of the elusive element. Their research is published today in the journal Nature.

Einsteinium is made at Oak Ridge National Laboratory’s High flux isotopic reactor as a by-product of the biannual production of californium-252 (another heavy element, synthesized in the lab, but which has commercial utility.) Advances in technology have meant that these radioactive elements can be made in the lab, without pyrotechnics destructive mid-20th century. The Oak Ridge reactor in Tennessee is one of the very few suppliers of californium-252.

“The reason they can create these elements is that they have this very high neutron flux, so they can just push further and further. [of their nucleon shells], “ Katherine Shield, a chemist at Lawrence Berkeley National Laboratory and co-author of the article, said during a video call. The initial product of the reactor is “just an absolute mess, a combination of all kinds of things,” Shield said, explaining that “it’s not just about making the element or making the isotope, but also about making the isotope. purify it so that we can do chemistry. with that.”

Heavy radioactive elements such as einsteinium and californium, as well as colloquial names like uranium and plutonium, are in the actinide group: elements 89 through 103 of the periodic table. Only some of them, like einsteinium and californium, are synthesized. Once a research team gets past the logistical work of safety protocols (to ensure that radioactive items, like all other laboratory equipment, are handled safely), the problems are mainly to ensure that ‘they have enough material to work with and that the material is pure. enough to deliver useful results. Extracted from the Californium production process, einsteinium can often be contaminated with the former.

The research team was working with just 200 nanograms of einsteinium, an amount about 300 times lighter than a grain of salt. According to Korey Carter, a current University of Iowa chemist and lead author of the study, one microgram (1,000 nanograms) was previously considered the lower limit for a sample size.

“There were questions of, ‘Will the sample survive?’ that we could prepare as best we could, ”Carter said on a video call. “Surprisingly, surprisingly, it worked.”

The team succeeded in measuring the binding distance of einsteinium-254 using x-ray absorption spectroscopy, in which you bombard the sample with x-rays (this line of investigation also required the construction of a specialized support for the sample, which would not collapse (under X-ray bombardment for about three days). The researchers looked at what happened to the light absorbed by the sample and found that the light emitted afterwards was shifted blue, meaning the wavelengths were shortened slightly. It was a surprise, as they had expected a redshift – longer wavelengths – and it suggests that einsteinium’s electrons may couple differently from other elements close to it on the board. periodic. Unfortunately, the team could not obtain the x-ray diffraction data due to californium contamination in their sample, which would cloud the results of the method.

Previously, researchers assumed they could extrapolate certain trends seen in lighter elements to heavier actinide elements, such as how they absorb light and how the size of atoms and ions from other elements, called lanthanides, decrease as their atomic number increases. But the new results suggest that the extrapolation may not be true.

“There has been a lot of great work over the past 20 years to gradually take the actinide series one step further, showing that… actinide chemistry has more to do,” Carter said. “The rules that we sort of developed for the little things might not work as well.”

Radioanalytical work had been done on einsteinium shortly after its discovery in the 1950s, but at the time, few studies were on actinides in general beyond their radioactive properties). Recent research has shown that einsteinium bond distances – the average length of the connection between the nuclei of two atoms in a molecule –were a little shorter than expected. The result, Carter said, is a “significant first data point.”

Like so many other scientists during this pandemic, the team was unable to follow-up experiences they had planned. When they finally returned to the lab, most of their sample was rotten. But as with any first step, this one will surely be followed by progress. It’s just a matter of when.