This sample was used to synthesize the new element tennessine for the first time in 2009 at the Joint Institute for Nuclear Research, Russia, after it was bombarded with calcium-48 ions for 150 days.

When compressed at room temperature to 7 GPa, α-berkelium transforms to the β modification, which has a face-centered cubic (fcc) symmetry and space group Fm3m.

This trivalent oxidation state (+3) is the most stable, especially in aqueous solutions,[19][20] but tetravalent (+4),[21] pentavalent (+5),[22] and possibly divalent (+2) berkelium compounds are also known.

The existence of divalent berkelium salts is uncertain and has only been reported in mixed lanthanum(III) chloride-strontium chloride melts.

[23][26][27] Berkelium does not react rapidly with oxygen at room temperature, possibly due to the formation of a protective oxide layer surface.

Analysis of the debris at the testing site of the first United States' first thermonuclear weapon, Ivy Mike, (1 November 1952, Enewetak Atoll), revealed high concentrations of various actinides, including berkelium.

The latter has a half-life of 351 years, which is relatively long compared to the half-lives of other isotopes produced in the reactor,[31] and is therefore undesirable in the disposal products.

[33] Although very small amounts of berkelium were possibly produced in previous nuclear experiments, it was first intentionally synthesized, isolated and identified in December 1949 by Glenn T. Seaborg, Albert Ghiorso, Stanley Gerald Thompson, and Kenneth Street Jr.

"[35] This tradition ended with berkelium, though, as the naming of the next discovered actinide, californium, was not related to its lanthanide analogue dysprosium, but after the discovery place.

This target was irradiated with 35 MeV alpha particles for 6 hours in the 60-inch cyclotron at the Lawrence Radiation Laboratory, University of California, Berkeley.

[35] Further separation was carried out in the presence of a citric acid/ammonium buffer solution in a weakly acidic medium (pH≈3.5), using ion exchange at elevated temperature.

The higher flux promotes fusion reactions involving not one but several neutrons, converting 239Pu to 244Cm and then to 249Cm: Curium-249 has a short half-life of 64 minutes, and thus its further conversion to 250Cm has a low probability.

[42] Thus, 249Bk is the most accessible isotope of berkelium, which still is available only in small quantities (only 0.66 grams have been produced in the US over the period 1967–1983[43]) at a high price of the order 185 USD per microgram.

Although its direct detection was hindered by strong signal interference with 245Bk, the existence of a new isotope was proven by the growth of the decay product 248Cf which had been previously characterized.

[50] A more detailed procedure adopted at the Oak Ridge National Laboratory was as follows: the initial mixture of actinides is processed with ion exchange using lithium chloride reagent, then precipitated as hydroxides, filtered and dissolved in nitric acid.

It is then treated with high-pressure elution from cation exchange resins, and the berkelium phase is oxidized and extracted using one of the procedures described above.

[50] Reduction of the thus-obtained berkelium(IV) to the +3 oxidation state yields a solution, which is nearly free from other actinides (but contains cerium).

[51] In order to characterize chemical and physical properties of solid berkelium and its compounds, a program was initiated in 1952 at the Material Testing Reactor, Arco, Idaho, US.

[43][52] This irradiation method was and still is the only way of producing weighable amounts of the element, and most solid-state studies of berkelium have been conducted on microgram or submicrogram-sized samples.

These facilities have similar power and flux levels, and are expected to have comparable production capacities for transcurium elements,[56] although the quantities produced at NIIAR are not publicly reported.

Berkelium(II) oxide, BkO, has been reported as a brittle gray solid but its exact chemical composition remains uncertain.

The most stable phase at low temperatures is isotypic with yttrium(III) fluoride, while upon heating to between 350 and 600 °C, it transforms to the structure found in lanthanum trifluoride.

It can be prepared by introducing hydrogen chloride vapors into an evacuated quartz tube containing berkelium oxide at a temperature about 500 °C.

An important phenomenon for radioactive solids has been studied on these two crystal forms: the structure of fresh and aged 249BkBr3 samples was probed by X-ray diffraction over a period longer than 3 years, so that various fractions of berkelium-249 had beta decayed to californium-249.

Berkelium(III) phosphate (BkPO4) has been prepared as a solid, which shows strong fluorescence under excitation with a green light.

[66] Thermal decomposition at about 600 °C in an argon atmosphere (to avoid oxidation to BkO2) of Bk2(SO4)3·12H2O yields the crystals of berkelium(III) oxysulfate (Bk2O2SO4).

[16] It is also useful as a source of the isotope californium-249, which is used for studies on the chemistry of californium in preference to the more radioactive californium-252 that is produced in neutron bombardment facilities such as the HFIR.

This target yielded the first 6 atoms of tennessine at the Joint Institute for Nuclear Research (JINR), Dubna, Russia, after bombarding it with calcium ions in the U400 cyclotron for 150 days.

Its critical mass is relatively high at 192 kg, which can be reduced with a water or steel reflector but would still exceed the world production of this isotope.

The low energy of electrons emitted from berkelium-249 (less than 126 keV) hinders its detection, due to signal interference with other decay processes, but also makes this isotope relatively harmless to humans as compared to other actinides.