Berkelium · element 97
The element it took 250 days of reactor time to stockpile, so that another element could be discovered
Key facts
Berkelium is named after a city, or rather a university, in the same way that terbium above it is named after the Swedish village of Ytterby. It was created at Berkeley in 1949, and since then the total amount ever produced across the world has only just exceeded a single gram. Almost all of that has been used up in research or has decayed.
For a long time berkelium seemed to have no purpose beyond filling a gap in the table. Then, in 2010, a 22-milligram sample became the target that yielded the first atoms of element 117, tennessine. Without berkelium, one of the newest elements would still be blank.
Where it is found
Berkelium is entirely synthetic. It does not survive from the formation of the Earth because its longest-lived isotope, berkelium-247, has a half-life of only about 1,400 years. Trace atoms may have been formed in nuclear tests, but none has been detected in nature.
It is produced by irradiating curium or americium targets with neutrons for many months in high-flux reactors, principally the High Flux Isotope Reactor at Oak Ridge National Laboratory in Tennessee. The result is mainly berkelium-249, which has a half-life of 330 days and gradually decays into californium-249. Because it decays so fast, berkelium samples are always changing, and any experiment must account for the californium growing inside them.
How it was discovered
Stanley Thompson, Albert Ghiorso and Glenn Seaborg produced berkelium in December 1949. They bombarded a few milligrams of americium-241 with alpha particles from the 60-inch cyclotron at Berkeley, then dissolved the target and used ion exchange chromatography to separate the products. The new element, berkelium-243, showed itself by characteristic decay and by emerging from the chromatography column exactly where an element below terbium should.
The discoverers chose the name berkelium for the city of Berkeley, home of the University of California, in the same spirit that terbium had been named for Ytterby. It was the fifth transuranium element found there. A visible quantity, a few billionths of a gram of berkelium chloride, was not produced until 1962, and the metal was first made in 1969.
What we use it for
Berkelium has no practical applications. It is far too rare and radioactive, and every microgram must be made to order. Its value is as a stepping stone to heavier elements and as a test of chemical theory. Berkelium-249 targets have been bombarded with calcium-48 at the Joint Institute for Nuclear Research in Dubna to produce tennessine, and with lighter ions to make isotopes of lawrencium and other elements.
Chemists study berkelium because it is the first actinide after plutonium where the +4 oxidation state is reasonably accessible in solution, echoing terbium and cerium among the lanthanides. Recent experiments have used tiny amounts to measure how berkelium binds to organic molecules, which helps chemists design better ways to separate actinides in nuclear waste.
Reading the numbers
Berkelium melts at about 990 °C, lower than gold, and boils near 2,630 °C. Its density of 14.8 grams per cubic centimetre is nearly twice that of iron and a little above lead. The configuration [Rn] 5f9 7s2 has nine electrons in the 5f shell and none in 6d, the pattern of a lanthanide-like actinide. Those f electrons are largely locked away, so berkelium usually forms +3 ions and behaves like a heavy version of terbium. Its first ionisation energy, about 601 kilojoules per mole, is typical of the later actinides. Berkelium's electron affinity is strongly negative in our data, which reflects the difficulty of forcing an extra electron onto an atom whose outer shells are already crowded.
Safety and the environment
Berkelium is a bone-seeking alpha emitter and is intensely radioactive gram for gram. Berkelium-249 also decays by beta emission, which needs shielding. It is handled only in hot cells and glove boxes at a handful of laboratories. Because so little exists, it poses no environmental threat, and its short half-lives mean any release would fade within a few thousand years. Its main relevance to waste is indirect: the californium it decays into is a strong neutron emitter.
Did you know?
- The total amount of berkelium ever made is around a gram, spread over more than seventy years of production.
- The 22-milligram target used to discover tennessine took about 250 days of reactor irradiation and 90 days of chemical purification to prepare.
- Berkelium-249 turns into californium-249 with a half-life of 330 days, so a sample is noticeably different after a year on the shelf.
- Berkelium is one of a small group of elements named after places in the United States; californium and tennessine are others.
- The first visible compound of berkelium, made in 1962, weighed about three billionths of a gram.
More in the actinides
The nearest neighbours of berkelium in the family, by atomic number.
See all 15 actinides on one page, or browse all 118 elements.
Frequently asked questions
What is berkelium used for?
Only research. Its most famous role was as the target material for creating tennessine, element 117, in 2010. It is also used to study how late actinides bond.
Is berkelium radioactive?
Yes, intensely. Its longest-lived isotope lasts about 1,400 years, and the commonly produced berkelium-249 has a half-life of under a year.
Where does berkelium get its name?
From Berkeley, California, where it was made in 1949. The naming echoed terbium, the element above it, which is named after a Swedish village.
How much berkelium exists?
Roughly a gram has ever been produced, and most of that has decayed or been consumed. Only milligram amounts exist at any one time.
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Written by Anthony. Updated September 2026. Numerical data from Periodic-Table-JSON (CC BY-SA), cross-checked against the Berkelium reference article. Spotted an error? Tell us.