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Optical Spectroscopy of Trans-Fermium Elements at SHIPTRAP

An ultra sensitive laser spectroscopic method is being developed for the investigation of the completely unknown atomic structure of the elements No and Lr. Such experiments aim in the investigation of relativistic effects. These, roughly speaking, originate from a shrinkage of the wave functions of inner shell electrons which, in turn, influence the binding energy of the valence electrons and thus the chemical properties. A direct approach to investigate relativistic effects may be to study first ionization potentials (IP) or even better, the atomic level schemes [1]. First experiments will be performed within the SHIPTRAP collaboration at No which will be produced via the fusion reaction Pb(Ca,2n)No. The reaction products, separated by SHIP, will be stopped in a buffer gas cell in which Resonance Ionization Spectroscopy (RIS) is performed with detection of the ionization process by the α-decay of No. The technique is similar to that developed for RIS at fission isomers [2]. The experimental setup is shown in Fig. 1. The reaction products with an energy of 40 MeV are injected into the argon buffer gas trap and stopped in the gas at an pressure of 100-300 mbar. The neutral part of about 15% will be ionized resonantly and guided by electric fields onto a detector which registers the α-decay radiation. After each detuning of the laser frequency of the first excitation step one has to wait for the decay of the accumulated ions. The symmetric construction offers the opportunity to collect on one detector ions, that are resonantly ionized while counting with the other one the activity collected at a different wavelength.