The heavy element einsteinium was first invented by the combustion of a hydrogen bomb on the island of Elugelab in the South Pacific in 1952 and is one of the shyest members of the periodic table; it does not occur naturally and is so unstable that it is difficult to get enough of the stuff long enough to actually 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 better understand 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 High Flux Isotope Reactor as a byproduct of the biennial production of californium-252 (another heavy, lab-synthesized element, but one that is commercially useful). Technological advancements have meant that these radioactive elements can be made in laboratory settings without the destructive pyrotechnics of the mid-20th century. The Oak Ridge, Tennessee reactor is one of the few suppliers of californium-252.
“The reason they can make these elements is because they have this very high flux of neutrons, so they can just push further and further out. [of their nucleon shells], “ Katherine Shield, a chemist at Lawrence Berkeley National Laboratory and co-author of the paper, said in a video conversation. The reactor’s original product 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, it’s also about purifying so we can do chemistry. with it. “
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Such heavy, radioactive elements as einsteinium and californium, as well as familiar names such as uranium and plutonium, are part of the actinide group: elements 89 to 103 on the periodic table. Only a few of these, such as einsteinium and californium, are synthesized. Once a research team is past the logistical work of safety protocols (to make sure that the radioactive elements, like any other laboratory material, are handled safely), the issues in the first place ensure that they have enough material to work with and that the material is pure. enough to provide actionable results. Einsteinium is extracted from the californium manufacturing process and can often be contaminated by the former.
The research team worked with just 200 nanograms of einsteinium, an amount about 300 times lighter than a grain of salt. According to Korey Carter, a chemist now at the University of Iowa and lead author of the study, a microgram (1,000 nanograms) was previously thought to be the lower limit for a sample size.
“There were questions, ‘Will the sample survive?’ that we could best prepare for, “Carter said in a video call.” Amazingly, it worked. “
The team managed to measure the bonding distance of einsteinium-254 using X-ray absorption spectroscopy, where you bombard the sample with X-rays (this line of research also required building a specialized container for the sample, one that would not crumble under X-ray bombardment in the course of about three days). The researchers looked at what happened to light absorbed by the sample and found that the light that was then emitted was blue-shifted, meaning the wavelengths were slightly shorter. This was a surprise, as they had expected a redshift – longer wavelengths – and this suggests that einsteinium’s electrons may couple differently than other elements near it on the periodic table. Unfortunately, the team was unable to obtain X-ray diffraction data due to a californium contaminant in their sample, which would cloud their results of the method.
Previously, researchers assumed that they could extrapolate certain trends in lighter elements to the heavier actinide elements, such as how they absorb light and how the size of the atoms and ions of other elements, called lanthanides, Reduce as their atomic numbers increase. But the new results suggest that extrapolation may not be accurate.
“A lot of good work has been done over the past 20 years to get further up the actinide series, showing that … actinide chemistry is more going on,” Carter said. “The rules we’ve developed for smaller things may not work very well.”
Shortly after its discovery in the 1950s, radioanalytic work had been done on einsteinium, but little was studied at the time about actinides in general beyond their radioactive properties). The recent research showed that the bonding distances of einsteinium – the average length of the bond between the nuclei of two atoms in a molecule –goods slightly shorter than expected. The result, Carter said, is a “meaningful first data point.”
Like so many other scientists during this pandemic, the team was unable to evaluate the follow-up experiments they planned. When they finally got back to the lab, most of their sample had decayed. But as with any first step, it will definitely be followed by steps. It’s just a matter of when.