Fission Cross Section of Berkelium-249 Between 0.7 and 3.0 MeV

The neutron-induced fission cross section of ²⁴⁹Bk was measured over the threshold region near 1 MeV by time-of-flight techniques in conjunction with the underground nuclear explosion, Physics-8. The cross section rises from 0.1 b at 0.7-MeV neutron energy to a plateau of ∼1.5 b from 1.6 to 3.0 MeV. Although our data extended down to 15-eV neutron energy, possible subthreshold fission in ²⁴⁹Bk was obscured by the presence in the sample of a small amount of its fissile daughter, ²⁴⁹Cf.