Berkelium Bk

Discovery

Berkelium was first produced in December 1949 at the University of California, Berkeley, by Stanley Thompson, Albert Ghiorso and Glenn Seaborg. They fired alpha particles from the 60-inch cyclotron at americium-241 and obtained berkelium-243, which has a half-life of about 4.5 hours.

The discovery took several years to achieve for two reasons. Enough americium had to be accumulated and fashioned into a usable target, and a new chemical procedure had to be devised to separate the element from its neighbours. Predicting that element 97 would behave like terbium, its lanthanide counterpart, the team designed an ion-exchange separation that picked it out.

At first only a few atoms could be studied. Visible amounts of berkelium compounds were obtained in the early 1960s after curium and other targets had spent long periods in high-flux reactors. Even today it is produced in small quantities at only a handful of facilities, notably the High Flux Isotope Reactor at Oak Ridge National Laboratory in Tennessee.

Origin of the name

Terbium, directly above berkelium in the periodic table, takes its name from the Swedish mining village of Ytterby. Seaborg's team followed suit and named element 97 after the city where it was discovered, Berkeley. The symbol is Bk. It joins the Ytterby elements as one of the best-known examples of an element named after a town.

Main uses

• Superheavy element synthesis: In 2009 Oak Ridge irradiated targets for about 250 days to make roughly 22 milligrams of berkelium-249. The material was sent to Dubna in Russia and bombarded with calcium-48, leading to the discovery of element 117, tennessine, in 2010.
• Source of californium: Berkelium-249 beta-decays into californium-249, which in turn has served as a target for making element 118.
• Actinide chemistry: Berkelium can exist in both the +3 and +4 oxidation states, making it a useful point of comparison in studies of the heavy actinides.
• It has no industrial or medical applications.

Isotopes

Berkelium has no stable isotopes. The longest-lived, berkelium-247, has a half-life of about 1,380 years but is difficult to produce. The isotope used in practice is berkelium-249, which reactors can make in relatively larger amounts; its half-life is about 330 days. Because that is less than a year, the tennessine experiment was a race: the target had to be made, flown across the world and used before too much of it decayed. The first isotope found, berkelium-243, lasts about 4.5 hours.

In everyday life

Berkelium is effectively absent from nature and has no connection with daily life. So little is made that most chemists never see any. As a radioactive substance it is expected to accumulate mainly in bone if taken into the body, and like other transuranium elements it is handled only inside sealed facilities.