First ever measurements of einsteinium

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Since element 99—einsteinium—was discovered in 1952 at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) from the debris of the first hydrogen bomb, scientists have performed very few experiments with it because it is so hard to create and is exceptionally radioactive. A team of Berkeley Lab chemists has overcome these obstacles to report the first study characterizing some of its properties, opening the door to a better understanding of the remaining transuranic elements of the actinide series.

https://phys.org/news/2021-02-discoveries-edge-periodic-table-einsteinium.html

https://en.m.wikipedia.org/wiki/Einsteinium