Determination of the first ionization potential of nine actinide elements by resonance ionization mass spectroscopy

Due to its high sensitivity, RIMS enables the precise determination of the first ionization potential of actinide elements with a sample size of less than or equal to 10(12) atoms. The actinide atoms under investigation are ionized in the presence of an electric field by multiple resonant laser excitation, and the ions are mass-selectively detected in a time-of-night spectrometer. The first ionization potential is obtained by scanning the wavelength of the laser used for the last excitation step across the ionization threshold W-th - indicated by a sudden increase of the ion count rate - at various electric field strengths. Extrapolation of W-th to zero electric field strength leads directly to the first ionization potential. The first ionization potentials (TP) of Am, Cm, Bk, Cf and Es were determined for the first time as IPAm = 5.9736(3) eV, IPCm, = 5.9914(2) eV, IPBk = 6.1979(2) eV, IPCf = 6. 2817(2) eV, IPEs = 6.3676(5) eV with samples of 10(12) atoms. Furthermore, the ionization potentials of Th, U, Np and Pu were remeasured.