[Triumf-seminars] TRIUMF ISAC Seminar today at 15:15

[postmaster@admin.triumf.ca]

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Date/Time: Wed 2006-04-12 at 15:15

Location:  Auditorium          

Speaker:   Peter Kunz (Nuclear Physics, U Mainz)

Title:     Hyperfine spectroscopy of fermium and status of nobelium spectroscopy at GSI

Abstract: Hyperfine spectroscopy of the element fermium and status report of the nobelium experiment 

H. Backe, A. Dretzke, S. Fritzsche 3, R.G. Haire 4, P. Kunz, W. Lauth, M. Sewtz and N. Trautmann 
Universitaet Mainz, Germany 
3 Universitaet Kassel, Germany, 
4 Oak Ridge National Laboratory, Oak Ridge, USA 

An interesting aspect of the heaviest actinides and the transactinides is the influence of increasing relativistic effects on the valence-electron configuration of the atoms and its consequences on chemical behavior. It also leads to the question if in the region of Z ? 100 a simple extrapolation of systematics of homologous lower period elements may still be applicable. In our work the atomic level structure of the element fermium (Z=100) was investigated for the first time with the Ion-Guide detected Resonance Ionization Spectroscopy (IGRIS) method [1]. This method combines element-selective Resonance Ionization Spectroscopy (RIS) in a buffer gas and mass-selective Ion-Guide Quadrupole Mass Separation (IGQMS). A sample of only 2.7 ·10^10 atoms of the isotope 255 Fm with a half-life of 20.1 h was available. It has been demonstrated with this experiment that a successful level search is possible with our laser spectroscopic technique even if the number of atoms is rather low and no experimental information on the level scheme is available. The two levels which were found have been predicted by MCDF calculations. Partial lifetimes were determined from saturation characteristics and term assignments were proposed. To get insight into the accuracy of such ab-initio MCDF predictions, further levels for the element fermium were sought for. In addition, we investigated the hyperfine splitting of the two already observed levels at energies of (25,099.8 ± 0.2) cm-1 and (25,111.8 ± 0.2) cm-1 with a laser band width of 1.5 GHz aiming in a determination of the hyperfine structure constants A and B. Despite a rather poor experimental resolution they were deduced by a best fit of a rate equation model to the experimental data, which takes into account saturation and optical pumping effects. These results allowed a discussion of the magnetic dipole and electric quadrupole moments of fermium in contrast to comparable actinides and lanthanides (e.g. einsteinium, holmium and erbium) [2]. 
In order to investigate even heavier elements like nobelium, which can only be produced in on-line facilities at rates of a few ions per second, we are currently developing an experimental procedure, based on Radiation detected Resonance Ionization Spectroscopy (RADRIS). Here, ions of the element under investigation are stopped in a buffer gas cell, neutralized and probed by tunable laser beams with the aim of finding atomic transitions by resonance io


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