Determination of the first ionization potential of berkelium and californium by resonance ionization mass spectroscopy

Resonance ionizationmass spectroscopy (RIMS) is used for the precise determination of the first ionizationpotential (IP) of transuranium elements. Small amounts of material (≈0.4 ng) are sufficient for these measurements due to the high sensitivity of RIMS enabling the investigation of the actinidesbeyond plutonium, which are accessible only in limited amounts and difficult to handle due to their high radioactivity. The method presented takes advantage of the dependence of the ionizationthreshold on an external static electricfield. With samples of 1012 atoms of 249Bk and 249Cf experimental values for the first ionizationpotentials of IPBk=49989(2) cm−1 and IPCf=50665(2) cm−1 were obtained.