structural:summarization, structural:scholar_edition
Preparation of isotopes

Berkelium is produced by bombarding lighter actinides uranium (U) or plutonium (Pu) with neutrons in a nuclear reactor. In a more common case of uranium fuel, plutonium is produced first by neutron capture (the so-called (n,γ) reaction or neutron fusion) followed by beta-decay:

Plutonium-239 is further irradiated by a source that has a high neutron flux, several times higher than a conventional nuclear reactor, such as the 85-megawatt High Flux Isotope Reactor (HFIR) at the Oak Ridge National Laboratory in Tennessee, US. The higher flux promotes fusion reactions involving not one but several neutrons, converting Pu to Cm and then to Cm:

Curium-249 has a short half-life of 64 minutes, and thus its further conversion to Cm has a low probability. Instead, it transforms by beta-decay into Bk:

The thus-produced Bk has a long half-life of 330 days and thus can capture another neutron. However, the product, Bk, again has a relatively short half-life of 3.212 hours and thus does not yield any heavier berkelium isotopes. It instead decays to the californium isotope Cf:

Although Bk is the most stable isotope of berkelium, its production in nuclear reactors is very difficult because its potential progenitor Cm has never been observed to undergo beta decay. Thus, Bk 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) at a high price of the order 185 USD per microgram. It is the only berkelium isotope available in bulk quantities, and thus the only berkelium isotope whose properties can be extensively studied.

The isotope Bk was first obtained in 1956 by bombarding a mixture of curium isotopes with 25 MeV α-particles. Although its direct detection was hindered by strong signal interference with Bk, the existence of a new isotope was proven by the growth of the decay product Cf which had been previously characterized. The half-life of Bk was estimated as 23 ± 5 hours, though later 1965 work gave a half-life in excess of 300 years (which may be due to an isomeric state). Berkelium-247 was produced during the same year by irradiating Cm with alpha-particles:

Berkelium-242 was synthesized in 1979 by bombarding U with B, U with B, Th with N or Th with N. It converts by electron capture to Cm with a half-life of 7.0 ± 1.3 minutes. A search for an initially suspected isotope Bk was then unsuccessful; Bk has since been synthesized.