DETERMINATION OF THE FIRST IONIZATION POTENTIAL OF ACTINIDE ELEMENTS BY RESONANCE IONIZATION MASS SPECTROSCOPY

摘要

Resonance ionization mass spectroscopy (RIMS) in the presence of an external static electric field has been used for the determination of photoionization thresholds. Extrapolation of the thresholds obtained with different electric field strengths to zero field strength directly leads to the first ionization potential (IP). The ionization potentials of the transplutonium elements americium, curium, berkelium and californium could be measured for the first time. Due to the high sensitivity of RIMS, samples of only 10(12) atoms have been used. The results are: IPAm = 5.9738(2) eV, IPCm = 5.9915(2) eV, IPBk = 6.1979(2) eV and IPCf = 6.2817(2) eV. The same technique was applied to thorium, neptunium and plutonium, yielding IPTh, = 6.3067(2) eV, IPNp = 6.2655(2) eV and IPPu = 6.0258(2) eV. Plotted as a function of the number of electrons N, the actinide ionization potentials can be approximated by two straight lines joining at the half-filled shell when normalized to ionization from the lowest f(N)s(2) level to the lowest f(N)s level. (C) 1997 Elsevier Science B.V. [References: 34]