X1-Experiment : Laser Spectroscopy


Laser Spectroscopy, Ion Mobility Measurements, and Ion Chemical Reaction Studies at Heavy Elements in a Buffer Gas Cell


The element fermium (Z = 100) has been investigated with the method of resonance ionization spectroscopy in a buffer gas cell. The experiments were carried out on a 46 pg sample of the isotope 255Fm with a half life time of 20.1 h, produced in the high flux nuclear reactor of the ORNL, Oak Ridge, USA. A wave number scan from 27,100 to 28,400 cm-1 was carried through to search for a level triplet with large Einstein-coefficients, as predicted by ab-initio Multi-Configuration-Dirac-Fock (MCDF) calculations, and five new levels were found. In addition, the two known levels at wave numbers (25,099.8 ± 0.2) cm-1 and (25,111.8 ± 0.2) cm-1 were studied with a laser band width of 1.5 GHz and hyperfine broadenings were observed.


From drift time measurements of ions in a buffer gas cell filled with argon, changes of the ion mobility for various heavy elements and their compounds were observed from which ionic radii changes were determined. The ionic radius of americium shrinks by (3.1 ± 1.3)% with respect to that of plutonium, and an increase of the radius by (28 ± 2)% of plutonium oxide with respect to plutonium was found.


Ion chemical reactions of erbium ions were studied online in an argon buffer gas cell to which reaction gases like oxygen (O2) or methane (CH4) were added. At the MP tandem accelerator facility of the MPI für Kernphysik in Heidelberg erbium ions with an energy of 50 MeV were implanted into the buffer gas cell. The online measured reaction constant kEr+O2 = (3.2 ± 0.4) ·10-10 cm3/(molecule · s) for the reaction Er+ + O2 → ErO+ + O agrees with a reference measurement kEr+O2,FT = (3.3 ± 0.4) · 10-10 cm3/(molecule · s) performed with a Fourier-Transformation-Mass-Spectrometer (FT/MS).