Decay properties of new isotopes 235Bk and 231Am

The new isotopes, 235Bk and its α-decay daughter 231Am, were investigated using the gas-filled recoil separator SHANS2. They were identified by measuring radioactive decay chains originating from 235Bk, which was produced via the 197Au(40Ar, 2n)235Bk reaction. Three correlated α-decay chains were assigned to 235Bk, from which the α-particle energy of 235Bk was measured to be 7632(17) keV. For 231Am, the α-particle energy and half-life were determined to be 7109(18) keV and 75−30+137 s, respectively. The α-decay branching ratio of 231Am was evaluated as 17−15+65%. A systematic analysis reveals significant discrepancies between the experimental data and the WS4+RBF theoretical predictions for the isotopes of Bk and Am, which warrant further investigation.