DETERMINATION OF THE FIRST IONIZATION-POTENTIAL OF 9 ACTINIDE ELEMENTS BY RESONANCE IONIZATION MASS-SPECTROSCOPY (RIMS)

The high sensitivity of 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. By multiple resonant laser excitat ion, the actinide atoms under investigation are ionized in the presenc e of an electric field, and the ions are mass-selectively detected in a time-of-flight spectrometer. The first ionization potential is obtai ned by scanning the wavelength of the laser used for the last excitati on step across the ionization threshold W-th-indicated by a sudden inc rease of the ion count rate-at various electric field strengths. Extra polation of W-th to electric field strength zero leads directly to the first;ionization potential. The first ionization potentials (TP) of A m, 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 ionizatio n potentials of Th, U, Np and Pu were remeasured. (C) 1998 Elsevier Sc ience S.A.